Aeroflex 2024, 2023, 2023B, 2025, 2023A User Manual

AM/FM SIGNAL GENERATORS

2023A, 2023B, 2025

Maintenance Manual

Document part no. 46892/377

AM/FM SIGNAL GENERATORS

2023, 2023A, 2023B, 2024 & 2025

Includes information on:

Option 1: No attenuator
Option 2: DC operation
Option 3: High power
Option 4: High stability frequency standard
Option 5: Rear panel connectors
Option 7: Fast pulse modulation
Option 10: 1 V peak mod input
Option 11: Fast pulse and high power
Option 12: SINAD

© IFR Ltd. 1999

No part of this book may be reproduced or transmitted in any form

or by any means, electronic or mechanical, including photocopying,

or recorded by any information storage or retrieval system, without

permission in writing by IFR Ltd.

Printed in the UK

Manual part no. 46882-377

Issue 1

8 March 1999

This manual provides servicing information down to a defined circuit area for the 2023, 2023A,
2023B, 2024 and 2025 AM/FM Signal Generators.

Intended audience

The book is intended for qualified service engineers and assumes a knowledge of the instrument to
a level covered in:

Operating Manual 46882-225 for 2023 and 2024
Operating Manual 46882-373 for 2023A, 2023B and 2025.

Structure

Chapter 1 Technical description

This includes block diagrams and detailed board circuit descriptions. The circuit
descriptions refer directly to the servicing diagrams contained in Chapter 7.

Chapter 2 Maintenance

Refer to this chapter for board and unit access, service policy and routine safety
testing and inspection.

Chapter 3 Adjustment procedures

Refer to this chapter for information on password use and adjustment procedures.

Chapter 4 Initial repair

What to do if the instrument shows no signs of life.

Chapter 5 Fault diagnosis

Based on error message reports; narrows the search down to a defined circuit area.

Chapter 6 Replaceable parts

Contains instrument and board component parts, and a section on miscellaneous
mechanical parts.

Chapter 7 Servicing diagrams

Contains interconnection drawings, board circuits and component layout
diagrams.

About this manual

Associated publications

Refer to the relevant Operating Manual (part number 46882-225 for 2023 and 2024, part number
46882-373 for 2023A, 2023B and 2025) for an up-to-date list of associated publications.

ii 46882-377

Contents

Precautions......................................................................................................................................................... iv

Précautions........................................................................................................................................................vii

Vorsichtsmaßnahmen
Precauz
Precauciones
Chapter 1 TECHNICAL DESCRIPTION

Chapter 2 MAINTENANCE...........................................................................................................................2-1

Chapter 3 ADJUSTMENT PROCEDURES .................................................................................................3-1

Chapter 4 INITIAL REPAIR .........................................................................................................................4-1

Chapter 5 FAULT DIAGNOSIS ....................................................................................................................5-1

Chapter 6 REPLACEABLE PARTS .............................................................................................................6-1

Chapter 7 SERVICING DIAGRAMS............................................................................................................7-1

ioni .......................................................................................................................................................xiii

.....................................................................................................................................................xvi

Adjustments..............................................................................................................................3-4

Recommended test equipment ................................................................................................3-7

Adjustment procedures............................................................................................................3-8

Adjustment procedures for instruments fitted with Option 3 or 11..................................3-22

Adjustment procedure tables................................................................................................3-24

Appendix A Calibration GPIB commands ........................................................................... A-1

Circuit notes..............................................................................................................................7-2

......................................................................................................................................... x

....................................................................................................1-1

46882-377 iii

PRECAUTIONS

Precautions

These terms have specific meanings in this manual:

WARNING

Information to prevent personal injury.

Information to prevent damage to the equipment.
Important general information.

Symbols used on this product

The meaning of hazard symbols appearing on the equipment is as follows:

Symbol Nature of hazard

General hazard

Dangerous voltage

Toxic hazard

Static-sensitive components

General conditions of use

This product is designed and tested to comply with the requirements of IEC/EN61010-1 ‘Safety
requirements for electrical equipment for measurement, control and laboratory use’, for Class I
portable equipment and is for use in a pollution degree 2 environment. The equipment is designed
to operate from an installation category I and II supply.

Equipment should be protected from the ingress of liquids and precipitation such as rain, snow,
etc. When moving the equipment from a cold to a hot environment, it is important to allow the
temperature of the equipment to stabilize before it is connected to the supply to avoid
condensation forming. The equipment must only be operated within the environmental conditions
specified in Chapter 1 ‘Performance data’ in the Operating manual, otherwise the protection
provided by the equipment may be impaired.

This product is not approved for use in hazardous atmospheres or medical applications. If the
equipment is to be used in a safety-related application, e.g. avionics or military applications, the
suitability of the product must be assessed and approved for use by a competent person.

WARNING

Electrical hazards (AC supply voltage)

iv 46882-377

This equipment conforms with IEC Safety Class I, meaning that it is provided with a protective
grounding lead. To maintain this protection the supply lead must always be connected to the
source of supply via a socket with a grounded contact.

Be aware that the supply filter contains capacitors that may remain charged after the equipment is
disconnected from the supply. Although the stored energy is within the approved safety
requirements, a slight shock may be felt if the plug pins are touched immediately after removal.

Fuses

Note that the internal supply fuse is in series with the live conductor of the supply lead. If
connection is made to a 2-pin unpolarized supply socket, it is possible for the fuse to become
transposed to the neutral conductor, in which case, parts of the equipment could remain at supply
potential even after the fuse has ruptured.

Removal of covers

Disconnect the supply before removing the covers so as to avoid the risk of exposing high voltage
parts. If any internal adjustment or servicing has to be carried out with the supply on, it must only
be performed by a skilled person who is aware of the hazard involved.

PRECAUTIONS

WARNING

Electrical hazards (DC supply voltage)

This equipment conforms with IEC safety Class III, meaning that for continued safety it must only
be connected to supplies and signal sources which conform to ‘Separated Extra-Low Voltage’
(SELV and SELV-E) voltage and insulation requirements. No hazardous voltages are generated
internally. See under ‘Performance data’ in Chapter 1 of the Operating Manual for the maximum
permitted voltage levels that can be applied.

WARNING

Fire hazard

WARNING

RF hazard

Make sure that only fuses of the correct rating and type are used for replacement.
If an integrally fused plug is used on the supply lead, ensure that the fuse rating is commensurate

with the current requirements of this equipment. See under ‘Performance data’ in Chapter 1 in the
Operating manual for power requirements.

Do not disconnect RF cables which are carrying high levels of RF power. High voltages, which
can cause RF burns, may be present at the end of the unterminated cables due to standing waves.

Switch off the transmitter or other source of RF power before disconnecting the cable from the
equipment.

WARNING

Toxic hazards

WARNING

Beryllia

46882-377 v

Some of the components used in this equipment may include resins and other materials which give
off toxic fumes if incinerated. Take appropriate precautions, therefore, in the disposal of these
items.

Beryllia (beryllium oxide) is used in the construction of the followin g
components in this equipment :

TR808 on AA1 and AA1/1;
TR1 and TR2 on AA2/1 and AA2/7.

PRECAUTIONS

This material, when in the form of fine dust or vapor and inhaled into the lungs, can cause a
respiratory disease. In its solid form, as used here, it can be handled quite safely although it is
prudent to avoid handling conditions which promote dust formation by surface abrasion.

Because of this hazard, you are advised to be very careful in removing and disposing of these
components. Do not put them in the general industrial or domestic waste or despatch them by
post. They should be separately and securely packed and clearly identified to show the nature of
the hazard and then disposed of in a safe manner by an authorized toxic waste contractor.

WARNING

Beryllium copper

Some mechanical components within this instrument are manufactured from beryllium copper.
This is an alloy with a beryllium content of approximately 5%. It represents no risk in normal use.

The material should not be machined, welded or subjected to any process where heat is involved.
It must be disposed of as “special waste”.

It must NOT be disposed of by incineration.

Static-sensitive components

The presence of static-sensitive components is indicated in the equipment by yellow disks, flags or
labels bearing the symbol
components being permanently damaged by static charges or fast surges:

1. If a static-sensitive component is to be removed or replaced, the following anti-static
equipment should be used:

• A work bench with a grounded conductive surface.

• Metallic tools grounded either permanently or by repeated discharges.

• A low-voltage grounded soldering iron.

. Certain handling precautions should be observed to prevent these

• A grounded wrist strap and a conductive grounded seat cover for the operator

2. If a printed board containing static-sensitive components (as indicated by warning disk or
flag) is removed, it must be temporarily stored in a conductive plastic bag.

3. As a general precaution, avoid touching the leads of a static-sensitive component. When
handling a new one, leave it in its conducting mount until it is required for use.

4. If using a freezer aerosol in fault finding, take care not to spray programmable ICs as this may
affect their contents.

Suitability for use

This equipment has been designed and manufactured by IFR Ltd. to generate VHF and UHF
signals for the testing of radio communications apparatus. IFR Ltd. has no control over the use of
this equipment and cannot be held responsible for events arising from its use other than for its
intended purpose.

whose outer clothing should not be of man-made fiber.

vi 46882/377

Précautions

Les termes suivants ont, dans ce manuel, des significations particulières:

PRECAUTIONS

WARNING

contient des informations pour éviter toute blessure au personnel.

contient des informations pour éviter les dommages aux équipements.

contient d’importantes informations d’ordre général.

Symboles

La signification des symboles liés à cet équipement est la suivante:

Symbole Nature du risque

Risques généraux

Tension dangereuse

Danger produits toxiques

Conditions générales d’utilisation

Ce produit a été conçu et testé pour être conforme aux exigences des normes CEI/EN61010-1
“Règles de sécurité pour appareils électriques de mesurage, de régulation et de laboratoire”, pour
des équipements Classe I portables et pour une utilisation dans un environnement de pollution de
niveau 2. Cet équipement est conçu pour fonctionner à partir d’une alimentation de catégorie I et
II.

Cet équipement doit être protégé de l’introduction de liquides ainsi que des précipitations d’eau,
de neige, etc... Lorsqu’on transporte cet équipement d’un environnement chaud vers un
environnement froid, il est important de laisser l’équipement se stabiliser en température avant de
le connecter à une alimentation afin d’éviter toute formation de condensation. L'appareil doit être
utilisé uniquement dans le cadre des conditions d'environnement spécifiées au chapitre 1
"Performance data" du manuel d'utilisation, toute autre utilisation peut endommager les systèmes
de protection.

Ce produit n’est pas garanti pour fonctionner dans des atmosphères dangereuses ou pour un usage
médical. Si l'équipement doit être utilisé pour des applications en relation avec la sécurité, par
exemple des applications militaires ou aéronautiques, la compatibilité du produit doit être établie
et approuvée par une personne compétente.

WARNING

Sécurité électrique (tension d’alimentation alternative)

!

Cet appareil est protégé conformément à la norme CEI de sécurité Classe 1, c’est-à-dire que sa
prise secteur comporte un fil de protection à la terre. Pour maintenir cette protection, le câble
d’alimentation doit toujours être branché à la source d’alimentation par l’intermédiaire d’une prise
comportant une borne de terre.

Notez que les filtres d’alimentation contiennent des condensateurs qui peuvent encore être chargés
lorsque l’appareil est débranché. Bien que l’énergie contenue soit conforme aux exigences de
sécurité, il est possible de ressentir un léger choc si l’on touche les bornes sitôt après
débranchement.

Fusibles

Notez que le fusible d’alimentation interne est en série avec la phase du câble d’alimentation. Si la
prise d’alimentation comporte deux bornes non polarisées, il est possible de connecter le fusible au

46882-377 vii

PRECAUTIONS

neutre. Dans ce cas, certaines parties de l’appareil peuvent rester à un certain potentiel même
après coupure du fusible

Retrait des couvercles

L’appareil doit être débranché avant de retirer les couvercles afin d’éviter tout contact avec les
éléments haute tension. Si toutefois un réglage interne ou une réparation nécessitent la présence
de l’alimentation, ils devront être effectués par une personne qualifiée et avisée des risques
encourus.

WARNING

Sécurité électrique (tension d’alimentation continue)

Cet équipement est conforme aux normes de sécurité CEI Classe III, c’est-à-dire qu’il ne doit être
connecté qu’à des sources d’alimentation ou de signaux qui suivent les recommandations de
tension et d’isolement du type ‘Tension extra-faible séparée’ (SELV at SELV-E). Aucune tension
dangereuse n’est générée en interne. “Performance data” dans le chapitre 1 du manuel
d’utilisation précise les niveaux de tension maximum acceptables en entrée.

WARNING

Risque lié au feu

Lors du remplacement des fusibles vérifiez l’exactitude de leur type et de leur valeur.
Si le câble d’alimentation comporte une prise avec fusible intégré, assurez vous que sa valeur est

compatible avec les besoins en courant de l’appareil. Pour la consommation, reportez-vous au
“Performance data” dans le chapitre 1 du manuel d’utilisation.

Danger RF

Ne jamais debrancher un câble RF connecté à une source de puissance RF en fonctionnement. Il
peut y avoir, à l'extrémité d'un câble non chargé, des tensions très importantes susceptibles de
causer des brûlures graves. Toujours éteindre la source de puissance RF avant de débrancher le
câble sur l'équipement.

WARNING

Danger produits toxiques

Certains composants utilisés dans cet appareil peuvent contenir des résines et d’autres matières qui
dégagent des fumées toxiques lors de leur incinération. Les précautions d’usages doivent donc
être prises lorsqu’on se débarrasse de ce type de composant.

WARNING

Le Béryllia

Le Béryllia (oxyde de Béryllium) entre dans la composition des composants suivants:
TR808 sur AA1 et AA1/1;

TR1 et TR2 sur AA2/1 et AA2/7.
Cette matière peut, lorsqu’elle est inhalée sous forme de vapeur ou de fine poussière, être la cause

de maladies respiratoires. Sous sa forme solide, comme c’est le cas ici, cette matière peut être
manipulée sans risque, bien qu’il soit conseillé d’éviter toute manipulation pouvant entraîner la
formation de poussière par abrasion de la surface.

Il est donc conseillé, pour éviter ce risque, de prendre les précautions requises pour retirer ces
composants et s’en débarrasser. Ne les jetez pas avec les déchets industriels ou domestiques ou ne
les envoyez pas par la poste. Il faut les emballer séparément et solidement et bien indiquer la
nature du risque avant de les céder, avec précautions, à une entreprise spécialisée dans le
traitement de déchets toxiques.

viii 46882/377

PRECAUTIONS

WARNING

Bronze au béryllium

Dans cet équipement,certaines pièces mécaniques sont à base de bronze au béryllium. Il s'agit d'un
alliage dans lequel le pourcentage de béryllium ne dépasse pas 5%. Il ne présente aucun danger en
utilisation normale.

Toutefois, cet alliage ne doit pas être travaillé, soudé ou soumis à un processus qui implique
l'utilisation d'une source de chaleur.

En cas de destruction, il sera entreposé dans un container spécial. IL ne devra pas être détruit par
incinération.

46882-377 ix

PRECAUTIONS

Vorsichtsmaßnahmen

Diese Hinweise haben eine bestimmte Bedeutung in diesem Handbuch:

WARNING

dienen zur Vermeidung von Verletzungsrisiken.

dienen dem Schutz der Geräte.

enthalten wichtige Informationen.

Symbole

Die Gefahrensymbole auf den Geräten sind wie folgt:

Symbol Gefahrenart

Allgemeine Gefahr

Gefährliche Spannung

Warnung vor giftigen Substanzen

Allgemeine Hinweise zur Verwendung

Dieses Produkt wurde entsprechend den Anforderungen von IEC/EN61010-1
“Sicherheitsanforderungen für elektrische Ausrüstung für Meßaufgaben, Steuerung und
Laborbedarf”, Klasse I transportabel zur Verwendung in einer Grad 2 verunreinigten Umgebung,
entwickelt und getestet. Dieses Gerät ist für Netzversorgung Klasse I und II zugelassen.

Das Gerät sollte vor dem Eindringen von Flüssigkeiten sowie vor Regen, Schnee etc. geschützt
werden. Bei Standortänderung von kalter in wärmere Umgebung sollte das Gerät wegen der
Kondensation erst nach Anpassung an die wärmere Umgebung mit dem Netz verbunden werden.
Das Gerät darf nur in Umgebungsbedingungen wie in Kapitel 1 "Leistungsdaten (Performance
data)" der Bedienungsanleitung beschrieben, betrieben werden; ansonsten wird der vom Gerät
vorgesehene Schutz des Anwenders beeinträchtigt.

Dieses Produkt ist nicht für den Einsatz in gefährlicher Umgebung (z.B. Ex-Bereich) und für
medizinische Anwendungen geprüft. Sollte das Gerät für den Einsatz in sicherheitsrelevanten
Anwendungen wie z.B. im Flugverkehr oder bei militaerischen Anwendungen vorgesehen sein, so
ist dieser von einer für diesen Bereich zuständigen Person zu beurteilen und genehmigen.

WARNING

Elektrische Schläge (Wechselspannungsversorgung)

Das Gerät entspricht IEC Sicherheitsklasse 1 mit einem Schutzleiter nach Erde. Das Netzkabel
muß stets an eine Steckdose mit Erdkontakt angeschlossen werden.

Filterkondensatoren in der internen Spannungsversorgung können auch nach Unterbrechung der
Spannungszuführung noch geladen sein. Obwohl die darin gespeicherte Energie innerhalb der
Sicherheitsmargen liegt, kann ein leichter Spannungsschlag bei Berührung kurz nach der
Unterbrechung erfolgen.

Sicherungen

Die interne Sicherung in der Spannungszuführung ist in Reihe mit der spannungsführenden
Zuleitung geschaltet. Bei Verbindung mit einer zweiadrigen, nicht gepolten Steckdose kann die
Sicherung in der Masseleitung liegen, so daß auch bei geschmolzener Sicherung Geräteteile immer
noch auf Spannungspotential sind.

x 46882/377

Abnahme von Abdeckungen

Die Spannungsversorgung muß vor Abnahme von Gehäuseabdeckungen unterbrochen sein, damit
hochspannungsführende Teile gefahrlos zugänglich sind. Falls Abgleiche oder Servicearbeiten
unter Spannung notwendig werden, dürfen solche Arbeiten nur von fachkundigem Personal
durchgeführt werden, das die Gefahren kennt.

PRECAUTIONS

WARNING

Elektrische Schläge (Gleichspannungsversorgung)

Dieses Gerät entspricht der IEC Sicherheitsklasse III. Aus Sicherheitsgründen darf es nur an
Netzgeräte und Signalquellen angeschlossen werden, die in Spannung und Isolation der SELV und
SELV-E Richtlinie genügen (“Getrennte Niederspannung”). Im Gerät werden keine gefährlichen
Spannungen erzeugt. Im Handbuch, Kapitel 1, “Performance data” (Leistungsdaten), werden die
anschließbaren Höchstspannungen definiert.

WARNING

Feuergefahr

Es dürfen nur Ersatzsicherungen vom gleichen Typ mit den korrekten Spezifikationen
entsprechend der Stromaufnahme des Gerätes verwendet werden. Siehe hierzu Kapitel 1
“Leistungsdaten (Performance data)” der Bedienungsanleitung.

WARNING

Hochfrequenzstrahlung

Lösen Sie keine Kabel an welchen größere Pegel von Hochfrequenzleistung anliegen. An den
nichtabgeschlossenen Enden von HF Kabeln können auf Grund von Stehwellen hohe Spannungen
auftreten. Diese verursachen unter Umständen Verbrennungen. Schalten Sie den Sender oder die
Quelle der HF-Leistung vor dem Lösen des HF-Kabels ab.

WARNING

Warnung vor giftigen Substanzen

In einigen Bauelementen dieses Geräts können Epoxyharze oder andere Materialien enthalten sein,
die im Brandfall giftige Gase erzeugen. Bei der Entsorgung müssen deshalb entsprechende
Vorsichtsmaßnahmen getroffen werden.

WARNING

Beryllium Oxid

Beryllium Oxid wird in den folgenden Bauelementen dieses Geräts verwendet:
TR808 auf AA1 und AA1/1;

TR1 und TR2 auf AA2/1 und AA2/7.
Als Staub inhaliert kann Beryllium zu Schädigungen der Atemwege führen. In fester Form kann

es ohne Gefahr gehandhabt werden, wobei Staubabrieb vermieden werden sollte.
Wegen dieser Gefahren dürfen diese Bauelemente nur mit der entsprechenden Vorsicht ausgebaut

und entsorgt werden. Sie dürfen nicht mit Industrie oder Hausmüll vermengt oder per Post
versandt werden. Sie müssen separat verpackt und entsprechend der Gefährdung markiert werden.
Die Entsorgung muß über einen autorisierten Fachbetrieb erfolgen.

46882-377 xi

PRECAUTIONS

WARNING

Beryllium Kupfer

In diesem Gerät sind einige mechanische Komponenten aus Berylium Kupfer gefertigt. Dies ist
eine Verbindung welche aus einem Berylliumanteil von ca. 5 % besteht. Bei normaler
Verwendung besteht kein Gesundheitsrisiko.

Das Metall darf nicht bearbeitet, geschweißt oder sonstiger Wärmebehandlung ausgesetzt werden.
Es muß als Sondermüll entsorgt werden.
Es darf nicht durch Verbrennung entsorgt werden.

xii 46882/377

Precauzioni

Questi termini vengono utilizzati in questo manuale con significati specifici:

PRECAUTIONS

WARNING

riportano informazioni atte ad evitare possibili pericoli alla persona.

riportano informazioni per evitare possibili pericoli all'apparecchiatura.

riportano importanti informazioni di carattere generale.

Simboli

Significato dei simboli di pericolo utilizzati nell’apparato:

Simbolo Tipo di pericolo

Pericolo generico

Tensione pericolosa

Pericolo sostanze tossiche

Condizioni generali d’uso

Questo prodotto è stato progettato e collaudato per rispondere ai requisiti della direttiva
IEC/EN61010-1 ‘Safety requirements for electrical equipment for measurement, control and
laboratory use’ per apparati di classe I portatili e per l’uso in un ambiente inquinato di grado 2.
L’apparato è stato progettato per essere alimentato da un alimentatore di categoria I e II.

Lo strumento deve essere protetto dal possibile ingresso di liquidi quali, ad es., acqua, pioggia,
neve, ecc. Qualora lo strumento venga portato da un ambiente freddo ad uno caldo, è importante
lasciare che la temperatura all’interno dello strumento si stabilizzi prima di alimentarlo per evitare
formazione di condense. Lo strumento deve essere utilizzato esclusivamente nelle condizioni
ambientali descritte nel capitolo 1 ‘Performance data’ del manuale operativo, in caso contrario le
protezioni previste nello strumento potrebbero risultare non sufficienti.

Questo prodotto non è stato approvato per essere usato in ambienti pericolosi o applicazioni
medicali. Se lo strumento deve essere usato per applicazioni particolari collegate alla sicurezza
(per esempio applicazioni militari o avioniche),occorre che una persona o un istituto competente
ne certifichi l'uso.

WARNING

Pericoli da elettricità (alimentazione c.a.)

Quest ’apparato è provvisto del collegamento di protezione di terra e rispetta le norme di sicurezza
IEC, classe 1. Per mantenere questa protezione è necessario che il cavo, la spina e la presa
d’alimentazione siano tutti provvisti di terra.

Il circuito d’alimentazione contiene dei filtri i cui condensatori possono restare carichi anche dopo
aver rimosso l’alimentazione. Sebbene l’energia immagazzinata è entro i limiti di sicurezza,
purtuttavia una leggera scossa può essere avvertita toccando i capi della spina subito dopo averla
rimossa.

46882-377 xiii

PRECAUTIONS

Fusibili

Notare che un fusibile è posto sul filo caldo del cavo di alimentazione. Qualora l’alimentazione
avvenga tramite due poli non polarizzati, è possibile che il fusibile vada a protezione del neutro
per cui anche in caso di una sua rottura, l’apparato potrebbe restare sotto tensione.

Rimozione dei coperchi

Prima di rimuovere i coperchi occorre scollegare la spina d’alimentazione onde evitare il rischio di
esposizione di parti ad alta tensione. Eventuali operazioni di manutenzione che richiedono la
presenza dell’alimentazione dovranno essere eseguite solo da parte di personale specializzato ed a
conoscenza dei pericoli coinvolti.

WARNING

Pericoli da elettricità (alimentazione a c.c.)

Questo strumento rispetta le norme IEC, classe III, e quindi, per una completa sicurezza, deve
essere collegato solo ad alimentatori e generatori di segnali che rispettano I requ isiti d i ten s ione ed
isolamento SELV e SELV-E (Separated Extra-Low Voltage). Nessuna tensione pericolosa è
generata al suo interno. Vedi capitolo 1 del manuale operativo per quanto concerne I livelli
massimi di tensione applicabili.

WARNING

Pericolo d’incendio

Assicurarsi che, in caso di sostituzione, vengano utilizzati solo fusibili della portata e del tipo
prescritti.

Se viene usata una spina con fusibili, assicurarsi che questi siano di portata adeguata ai requisiti di
alimentazione richiesti dallo strumento. Tali requisiti sono riportati nel cap. 1 “Performance data”
del manuale operativo.

WARNING

Rischio a RF

Non sconnettere cavi RF sui quali si stia trasmettendo un segnale RF ad alta potenza. Un'alta
tensione, che può causare bruciature, potrebbe essere presente alla fine di cavi non terminati a
causa delle onde stazionarie. Spegnere il trasmettitore od altra sorgente di segnale RF prima di
disconnettere il cavo dall'apparato.

WARNING

Pericolo sostanze tossiche

Alcuni dei componenti usati in questo strumento possono contenere resine o altri materiali che, se
bruciati, possono emettere fumi tossici. Prendere quindi le opportune precauzioni nell’uso di tali
parti.

WARNING

Berillio

xiv 46882/377

Berillio (ossido di berillio) è utilizzato nella costruzione dei seguenti componenti di
quest’apparato:

PRECAUTIONS

TR808 schema AA1 e AA1/1;
TR1 e TR2 schema AA2/1 e AA2/7.

Questo materiale, se inalato sotto forma di polvere fine o vapore, può causare malattie respiratorie.
Allo stato solido, come è usato qui, può essere maneggiato con sufficiente sicurezza anche se è
prudente evitare condizioni che provochino la formazione di polveri tramite abrasioni superficiali.

A cause di questi pericoli occorre essere molto prudenti nella rimozione e nella locazione di questi
componenti. Questi non devono essere gettati tra i rifiuti domestici o industriali né. vanno spediti
per posta. Essi devono essere impacchettati separatamente ed in modo sicuro e devono indicare
chiaramente la natura del pericolo e quindi affidate a personale autorizzato.

WARNING

Rame berillio

Alcuni componenti meccanici in questo strumento sono realizzati in rame berillio. Si tratta di una
lega con contenuto di berillio di circa il 5%, che non presenta alcun rischio in usi normali.

Questo materiale non deve essere lavorato, saldato o subire qualsiasi processo che coinvolge alte
temperature.

Deve essere eliminato come "rifiuto speciale". Non deve essere eliminato tramite "inceneritore".

46882-377 xv

PRECAUTIONS

Precauciones

Estos términos tienen significados específicos en este manual:

WARNING

contienen información referente a prevención de daños personales.

contienen información referente a prevención de daños en equipos.

contienen información general importante.

Símbolos

Los significados de los símbolos de peligro que aparecen en los equipos son los siguientes:

Símbolo Naturaleza del peligro

Peligro general

Voltaje peligroso

Aviso de toxicidad

Condiciones generales de uso

Este producto ha sido diseñado y probado para cumplir los requerimientos de la normativa
IEC/EN61010-1 “Requerimientos de la normativa para equipos eléctricos de medida, control y uso
en laboratorio”, para equipos clase I portátiles y para uso en un ambiente con un grado de
contaminación 2. El equipo ha sido diseñado para funcionar sobre una instalación de alimentación
de categorías I y II.

Debe protegerse el equipo de la entrada de líquidos y precipitaciones como nieve, lluvia, etc.
Cuando se traslada el equipo de entorno frío a un entorno caliente, es importante aguardar la
estabilización el equipo para evitar la condensación. Sólo debe utilizarse el aparato en las
condiciones ambientales especificadas en el capítulo 1 “Especificaciones” o “Performance data”
del Manual de Instrucciones/Manual de Operación, en caso contrario la propia protección del
equipo puede resultar dañada.

Este producto no ha sido aprobado para su utilización en entornos peligrosos o en aplicaciones
médicas. Si se va a utilizar el equipo en una aplicación con implicaciones en cuanto a seguridad,
como por ejemplo aplicaciones de aviónica o militares, es preciso que un experto competente en
materia de seguridad apruebe su uso.

WARNING

Nivel peligroso de electricidad (tensión de red)

Este equipo cumple las normas IEC Seguridad Clase 1, lo que significa que va provisto de un
cable de protección de masa. Para mantener esta protección, el cable de alimentación de red debe
de conectarse siempre a una clavija con terminal de masa.

Tenga en cuenta que el filtro de red contiene condensadores que pueden almacenar carga una vez
desconectado el equipo. Aunque la energía almacenada está dentro de los requisitos de seguridad,
pudiera sentirse una ligera descarga al tocar la clavija de alimentación inmediatamente después de
su desconexión de red.

Fusibles

Se hace notar que el fusible de alimentación interno está enserie con el activo del cable de
alimentación a red. Si la clavija de alimentación de red cuenta con sólo dos terminales sin
polaridad, el fusible puede pasar a estar en serie con el neutro, en cuyo caso existen partes del
equipo que permanecerían a tensión de red incluso después de que el fusible haya fundido.

xvi 46882/377

Para retirar las tapas

Desconectar de red antes de retirar las tapas para evitar el riesgo que supone tener accesibles
aquellas partes del equipo expuestas a alta tensión. Aquellas operaciones que requieran tener
alimentación con las tapas abiertas para mantenimiento o ajuste deben de ser realizadas por
personal cualificado, que esté al tanto de los riesgos implicados.

PRECAUTIONS

WARNING

Nivel peligroso de electricidad (tensión de alimentación DC)

WARNING

Este equipo cumple con la norma de seguridad IEC clase III, lo que significa que para total
seguridad debe ser conectado a alimentaciones y fuentes de señal que cumplan los requerimientos
de tensión y aislamiento “Tensión Separada Extra-Baja” (SELV y SELV-E). Ninguna tensión
generada internamente implica riesgo para el operario.

En el capítulo 1 “Especificaciones” del Manual de Instrucciones/Manual de Operación podrá
encontrar los valores máximos permitidos que pueden aplicarse.

Peligro de incendio

Asegúrese de utilizar sólo fusibles del tipo y valores especificados como repuesto.
Si se utiliza una clavija con fusible incorporado, aseg úrese de que los valores del fusible

corresponden a los requeridos por el equipo. Ver sección de especificaciones del capítulo 1 del
Manual de Instrucciones/Manual de Operación/Funcionamiento para comprobar los requisitos de
alimentación.

WARNING

Peligro de RF

No desconecte cables de RF que transporten niveles altos de potencia de RF. Es posible la
presencia de altas tensiones, capaces de causar quemaduras por RF, en el extremo del cable sin
terminar, debido a ondas estacionarias. Desactive el transmisor u otra fuente de potencia de RF
antes de desconectar el cable de los equipos."

WARNING

Aviso de toxicidad

Alguno de los componentes utilizados en este equipo pudieran incluir resinas u otro tipo de
materiales que al arder produjeran sustancias tóxicas, Por tanto, tome las debidas precauciones en
la manipulación de esas piezas.

WARNING

Berilio

Berilio (óxido de berilio), se ha utilizado en la fabricación de los siguientes componentes del
equipo:

TR808 en AA1 y AA1/1;
TR1 y TR2 en AA2/1 y AA2/7.

La inhalación de este material, en forma de polvo fino o vapor, entrando en los pulmones, puede
ser causa de enfermedades respiratorias. En forma sólida, como se utiliza en este caso, puede
manipularse con bastante seguridad, aunque se recomienda no manejarlo en aquellas condiciones
que pudieran favorecer la aparición de polvo por abrasión de la superficie.

46882-377 xvii

PRECAUTIONS

Por todo lo anterior, se recomienda tener el máximo cuidado al reemplazar o deshacerse de estos
componentes, no tirándolos en basuras industriales o domésticas y no utilizar el correo para su
envío. Deben, ser empaquetados de forma segura y separada, y el paquete debidamente etiquetado
e identificado, señalando claramente la naturaleza del riesgo y ponerlo a disposición de un
destructor autorizado de productos tóxicos.

WARNING

Berilio-cobre

Algunos componentes mecánicos contenidos en este instrumento incorporan berilio-cobre en su
proceso de fabricación. Se trata de una aleación con un contenido aproximado de berilio del 5%,
lo que no representa ningún riesgo durante su uso normal.

El material no debe ser manipulado, soldado, ni sometido a ningún proceso que implique la
aplicación de calor.

Para su eliminación debe tratarse como un "residuo especial". El material NO DEBE eliminarse
mediante incineración.

xviii 46882/377

Contents

Chapter 1

TECHNICAL DESCRIPTION

Introduction....................................................................................................................................1-3

Synthesizer..............................................................................................................................1-3

RF processing
LF processing

AA1, AA1/1 RF board

Carrier frequency synthesis
RF board: Carrier generation (sheet 1)
RF board: VCXO loop (sheet 2)
RF board: Synthesizer (sheet 3)
RF board: Loop filter and autocal (sheet 4)
RF board: FM drive (sheet 5)
RF board: Level m
RF board: Frequency generator (sheet 7)
RF board: Interface and attenuator drive (sheet 8)
RF board: Output am

AA2 Attenuator board

Circuit functions

AA2/1 High power attenuator board

Circuit functions
High power attenuator board: Pulse m
High power attenuator board: Power am

AA2/2 Signal output board

Circuit function

AA2/5 Fast pulse m

Circuit functions
Fast pulse m
Fast pulse m

AA2/7 Fast pulse and high power board

Circuit functions
Fast pulse and high power board: Pulse m
Fast pulse and high power board: Attenuator (sheet 3)
Fast pulse and high power board: Power am

AB1, AB1/1 Control board

Introduction...........................................................................................................................

Control board: Microprocessor and m
Control board: DSP audio generator (sheet 2)
Control board: Interrupts and serial interface (sheet 3)
Control board: M
Control board: Standard selection (AB1 sheet 5, AB1/1 sheet 6)
Control board: Interface (AB1 sheet 6, AB1/1 sheet 7)
Control board: PSU filtering and regulation (AB1 sheet 7, AB1/1 sheet 9)
Control board: Power supplies (AB1 sheet 8)

Control board: 31 V dc power supply
AB2 SINAD board
AC1 Backlight inverter board
AF1 Front panel
AC power supply
AC/DC power supply

.........................................................................................................................1-3

..........................................................................................................................1-4

..................................................................................................................1-7

....................................................................................................1-7

...................................................................................1-7

.............................................................................................1-8

..............................................................................................1-9

..........................................................................1-10

...............................................................................................1-12

odulator (sheet 6)....................................................................................1-13

.............................................................................1-14

...............................................................1-16

plifier (sheet 9).................................................................................... 1-18

................................................................................................................1-19

...................................................................................................................1-19

...........................................................................................1-20

...................................................................................................................1-20

od & attenuator (sheet 1)..........................................1-21

p & RPP (sheet 2)................................................. 1-21

.........................................................................................................1-22

.....................................................................................................................1-22

odulator board.............................................................................................1-22

...................................................................................................................1-22

odulator board: Pulse mod (sheet 1).................................................................1-23

odulator board: RPP and atten (sheet 2) ...........................................................1-23

.....................................................................................1-24

...................................................................................................................1-24

od (sheet 2).........................................................1-24

........................................................1-24

p & RPP (sheet 4)........................................... 1-25

.........................................................................................................1-26

1-26

emory (sheet 1).........................................................1-26

......................................................................1-28

........................................................1-30

odulation and level (AB1 sheet 4, AB1/1 sheets 4 & 5)...........................1-34

........................................1-35

........................................................1-36

.........................1-37

......................................................................1-39

(AB1/1 sheet 8)........................................................ 1-39

......................................................................................................................1-39

.....................................................................................................1-39

..........................................................................................................................1-40

.........................................................................................................................1-40

...................................................................................................................1-40

46882-377 1-1

TECHNICAL DESCRIPTION

List of figures

Fig. 1-1 Signal generator block schematic...................................................................................1-5

Fig. 1-2 100 MHz phase-locked loop...........................................................................................1-8

Fig. 1-3 Frequency synthesis

g. 1-4 FM/ϕM drive................................................................................................................1-13

Fi
Fig. 1-5 Frequency band selection
Fig. 1-6 Microprocessor and control block diagram
Fig. 1-7 Frequency standard selection
Fig. 1-8 Block diagram

List of tables

Table 1-1: Carrier generation.....................................................................................................1-7

Table 1-2: Attenuator board identification...............................................................................1-11

Table 1-3:
Table 1-4:
Table 1-5:
Table 1-6:
Table 1-7:
Table 1-8:
Table 1-9:
Table 1-10:
Table 1-11:
Table 1-12:
Table 1-13:
Table 1-14:

.....................................................................................................1-10

.............................................................................................1-16

..................................................................1-27

.......................................................................................1-36

of AC/DC power supply module .........................................................1-41

Attenuator control settings......................................................................................1-12

Frequency band selection .......................................................................................1-15

Attenuator selection................................................................................................1-17

Interrupts and chip selects ......................................................................................1-28

Memory bank addressing........................................................................................1-28

Interrupt lines..........................................................................................................1-31

Interrupt lines..........................................................................................................1-31

Latch control lines..................................................................................................1-32

Buffered chip selects ..............................................................................................1-33

Latch control lines..................................................................................................1-33

Buffered chip selects ..............................................................................................1-33

Power supplies........................................................................................................1-40

1-2 46882-377

Introduction

The 2023, 2023A, 2023B, 2024 and 2025 AM/FM Signal Generators cover the following
frequency ranges:

9 kHz to 1.2 GHz 2023 and 2023A
9 kHz to 2.05 GHz 2023B
9 kHz to 2.4 GHz 2024
9 kHz to 2.51 GHz 2025

Output levels from -140 dBm to +13 dBm are available. Factory fitted options are available to
extend the level to +25 dBm (+19 dBm above 1.2 GHz) and to provide SINAD measurement
capability. Fig. 1-1 is a block diagram of the frequency synthesis and signal processing circuits.

Synthesizer

A VCXO operating at 100 MHz is phase locked to the internal (or external) frequency standard
using a phase comparator at 10 MHz. The VCXO signal is divided by 20 to give a 5 MHz
reference frequency for the fractional-N loop phase comparator.

A fractional-N loop is used to lock a multiplied low-noise VCO to the reference with a resolution
of l Hz. The VCO tunes from 400 to 535 MHz and is multiplied by three, four or five to yield a
signal in the range 1.2 to 2.51 GHz. A high speed programmable divider is used to divide the
multiplied VCO frequency down to 5 MHz and a phase comparator compares this signal with the
reference derived from the VCXO. The output from the phase comparator corrects the VCO
frequency. In order to provide the required division ratio, the programmable divider is required to
act as a fractional divider. The fractional-N gate array controls the division ratio of the
programmable divider. The variation of this division ratio by the controller enables the loop to
lock, with non-integer division ratios, to the reference with the resolution of 1 Hz without
introducing spurious signals.

FM is produced using a two-point modulation scheme. The FM signal is inserted into the loop by
summing the FM signal with the VCO tune line to modulate the VCO directly. Simultaneously,
the FM signal is fed to the fractional-N controller via a 1-bit oversampled A-D converter which
converts an analogue input into a bit stream of ‘1’s and ‘0’s. The controller uses this input to
modulate the division ratio in sympathy with the modulation. This allows frequencies less than
the loop bandwidth, including DC, to modulate the output frequency.

In order to maintain good FM performance of the two-point modulation system, the VCO FM
tracking characteristics are required to be known. The sensitivity of the FM system via the 1-bit
oversampled A-D converter is VCO independent and accurately calibrated by a DC calibration
system. The VCO tracking is derived by an automatic FM SELFCAL routine during calibration.
During an FM SELFCAL, the error signal on the tune line, for a frequency near the loop
bandwidth, is monitored while varying the FM calibration numbers, allowing the variation in VCO
sensitivities to be calibrated out. This will remove any perturbation of FM flatness near the loop
bandwidth due to mismatch of two modulation paths.

TECHNICAL DESCRIPTION

RF processing

The VCO on board AA1 operates in the range 400 to 535 MHz and feeds to a harmonic generator
whose 3rd, 4th and 5th harmonics are selected by voltage-tuned band-pass filters to pro vide a
frequency in the range 1.2 to 2.4 GHz (2.51 GHz on board AA1/1). To generate frequencies
below 1.2 GHz this signal is divided by factors of two to produce frequencies in the range 10 MHz
to 1.2 GHz. A bank of switched half octave harmonic filters follows which is used to reduce
unwanted harmonics at the output. Then the signal passes through the amplitude modulator where
the output level envelope is controlled. The output from the modulator is peak detected. For
frequencies less than 10 MHz the signal is mixed with an input from the 100 MHz VCXO. The
resulting output in the frequency range 9 kHz to 2.4 or 2.51 GHz is fed from the output amplifier
to attenuator board AA2. For pulse operation the signal is taken to the pulse modulator which
operates in the range 30 MHz to 2.51 GHz. Otherwise the pulse modulator is bypassed and the
signal is fed to the output attenuator. This is controlled by relays and provides attenuation in steps
of 11 dB up to 132 dB. The attenuator also includes an RPP (Reverse Power Protection) system to
protect the instrument from accidental application of reverse power.

46882-377 1-3

TECHNICAL DESCRIPTION

LF processing

The LF processing all takes place on control board AB1 or AB1/1, and may be conveniently
subdivided into the following major functional elements.

LF output

A DSP (Digital Signal Processor) is used to generate the audio frequency signals used for internal
modulation. One output from the DSP is used to supply the front panel LF OUTPUT socket.

For external modulation the signal applied to the EXT MOD INPUT socket first passes through
AC/DC coupling selection and then can either be applied directly or via an ALC (Automatic Level
Control) circuit to the audio multiplexers. The external direct signal can also be summed with the
audio frequency from the DSP.

AM and level control

For amplitude modulation the modulation depth is set by a 12-bit A-D converter. A second A-D
converter is used to produce the ALC reference for the RF board. Square law correction is applied
to both signals.

FM/ϕM

For frequency modulation the signal amplitude controls the FM deviation. For phase modulation
the signal is passed through a differentiator circuit.

1-4 46882-377

TECHNICAL DESCRIPTION

Fig. 1-1 Signal generator block schematic

46882-377 1-5

TECHNICAL DESCRIPTION

1-6 46882-377

AA1, AA1/1 RF board

Carrier frequency synthesis

The RF carrier of the instrument should be as clean in frequency (and level) as possible. To
achieve this goal the instrument relies on a single-loop fractional-N Synthesizer scheme and a
harmonic multiplier and UHF oscillator covering the fundamental range from 1.2 to 2.4 GHz
(AA1) or 1.2 to 2.51 GHz (AA1/1). Using this approach minimizes the RF processing circuitry
normally associated with conventional frequency doubling or mixing schemes.

A carrier frequency resolution of 1 Hz cannot be achieved easily without the use of non-integer
division. In this instrument this operation is controlled by a dedicated ASIC which modifies the
division ratio of a programmable divider so that the average frequency is a non-integer division of
the input.

RF board: Carrier generation (sheet 1)

Frequencies from 1.2 to 2.4 GHz (AA1) or 1.2 to 2.51 GHz (AA1/1) are generated by
multiplication from a 400 to 535 MHz low-noise oscillator. The tuned circuit is formed by C102,
C108, varactor diodes D101 to D106 and printed inductors. A maintaining transistor TR101 is
tapped into the tuned circuit. The oscillator is tuned by a differential voltage applied to the
varactor diodes via L101 to L103. The VCO TUNE LOW line is used to phase lock the oscillator
and inject FM whilst the VCO TUNE HIGH line is used to pre-steer the VCO.

The signal from the VCO is buffered by IC101 and then amplified by TR102 to provide a suitable
level to drive the harmonic multiplier. The collector of TR102 is tuned by L104, C114 and C116.
Harmonics are generated by D107 which acts as a step recovery diode. The diode is self-biased to
improve the efficiency of harmonic generation by the network R110, R108 and C111. The
harmonics generated by D107 are filtered by a four stage band-pass filter with a centre frequency
in the range of 1.2 to 2.4 GHz (AA1) or 1.2 to 2.5 GHz (AA1/1). Each filter stage is formed by a
pair of parallel coupled lines. Each line is capacitively loaded at one end by a pair of back-to-back
varactor diodes to allow tuning over an octave. The stages are separated by buffer amplifiers
IC104 to IC107. These amplifiers compensate for the loss and frequency response inherent in
each filter stage and provide isolation so that tuning of the stages is independent. A pad at the
output of each buffer amplifier increases the isolation and provides a better match to the input of
the next filter stage. The filtered signal at the output of IC107 is split by R149 and R150 to feed
the synthesizer dividers (sheet 3) and the output dividers (sheet 7). The filter stages are tuned by a
voltage in the range of 1 to 24 V (AA1) or 1 to 31 V (AA1/1) derived from octal DAC IC103.
This is applied via scaling amplifier IC102a and buffer IC102b. Diodes D125 and D126 allow fast
tuning by shorting out R124 to reduce the charging time constant and so shorten the filter settling
time whenever the frequency is changed. A 1.25 V reference for the DAC is provided by IC108
via IC102c. Table 1-3 below gives the relationship between the VCO frequency, the harmonic
and the final output frequency.

TECHNICAL DESCRIPTION

When the varactor diodes (D108 - D123) need replacing, they must be replaced as a set. If
the alternative type diodes are fitted, resistor R717 will need repositioning accordingly.

Table 1-1: Carrier generation

Output frequency

(MHz)

1200 - 1600 3 400 - 533.3
1600 - 2000 4 400 - 500
2000 - 2510 5 400 - 502

Harmonic number

(N)

VCO frequency

(MHz)

46882-377 1-7

TECHNICAL DESCRIPTION

RF board: VCXO loop (sheet 2)

100 MHz VCXO

The 100 MHz VCXO is used to derive all of the clock signals necessary for the fractional-N
Synthesizer. The use of a high frequency eliminates the need for a second phase-locked oscillator
to generate the necessary local oscillator frequency for the BFO. The reference divider provides a
5 MHz clock for the fractional-N Synthesizer and the FM A-D converter.

VCXO operation

The 100 MHz oscillator is built around TR201. Crystal XL201 together with L202 and D201
provide a series resonant circuit in the emitter circuit of TR201. At resonance it increases the gain
of the common-emitter stage and together with 180 degree phase shift network L204, C216, C215,
C219 and C220 connected between the base and collector of TR201 provides the necessary
conditions for oscillation. L203 tunes out the parasitic capacitance of the crystal package and
prevents other spurious oscillations from occurring.

A facility to fine tune the phase shift network is provided by C215. At the resonant frequency, the
circuit operates at maximum power levels when the correct phase shift is achieved around the
transistor. TR202 provides a buffered signal to the VCXO loop divider IC205. A second buffer,
TR203 provides local oscillator drive (at typically +3 dBm) to the BFO mixer (sheet 9). The BFO
DRIVE line to TR204 allows the second buffer amplifier to be powered down when the BFO is
not in use to prevent leakage of the 100 MHz LO onto the instrument output.

100 MHz phase-locked loop

The VCXO is used to provide a reference signal to the fractional-N loop and to the BFO band
mixer and is locked to the 10 MHz frequency standard provided from control board AB1 or AB1/1
via PLAB. The buffered 100 MHz signal is divided down to 10 MHz before phase comparison.
An integrator and active low-pass filter ensures the removal of the reference frequency from the
VCXO tune line. A window comparator monitors the VCXO tune line to detect when the
oscillator is outside its normal operating range. The block diagram of the phase-locked loop is
shown in Fig. 1-2.

Fig. 1-2 100 MHz phase-locked loop

1-8 46882-377

Loop operation

The 100 MHz signal from the VCXO is buffered and amplified by TR205 to yield a CMOS logic
compatible signal for the dividers which follow. The signal is divided by two by IC205a and then
by five by IC202 to give 10 MHz for phase comparison. IC201 and IC203 form the loop
phase-frequency comparator. R203 and C208 remove the fast edges from the output of the phase
detector. A broken integrator is formed around IC204b. This has a break frequency of 80 Hz and
a gain at high frequency of four. IC204a, which follows, is a second-order active low-pass filter
with a cut-off of 700 Hz and a gain of two. The resulting loop bandwidth is approximately
150 Hz. The output from the active low-pass filter is further filtered by R212 and C213 to remove
any high frequency signals.

IC204c and d form a window comparator which detects when the VCXO tuning voltage range is
exceeded. The outputs from the comparators are attenuated to logic levels by R216 to R219 to
give VCXO LOOP HIGH and VCXO LOOP LOW lines to provide status interrupts to the main
processor via IC704 (sheet 8).

RF board: Synthesizer (sheet 3)

Synthesizer operation

Frequency synthesis control is performed by a dedicated ASIC, IC305. This generates all of the
necessary division ratios for programmable divider IC307 to synthesize any frequency within the
range 1.2 to 2.4 GHz (AA1) or 1.2 to 2.51 GHz (AA1/1). Synthesizer operation is summarized in
Fig. 1-3.

The 1.2 to 2.51 GHz (AA1) or 1.2 to 2.51 GHz (AA1/1) input signal from the harmonic generator
(sheet 1) is buffered by TR305 (sheet 3) to prevent divider spurious signals from IC309 reaching
the instrument output. Signal feedback is not used with this stage, to give high reverse isolation.

The buffered signal is divided by two by IC309 and then amplified by IC308 to obtain a sufficient
level to drive the input of programmable divider IC307. The programmable divider is used to
provide integer division in the range 120 to 240. Fractional division is achieved by the
modification of the integer division ratios, under the control of ASIC IC305, in such a way that the
average frequency over time is not an integer division ratio of the original. Control inputs to
IC307 are TTL compatible. The control outputs from ASIC IC305 are inverted by IC306 to
provide the correct polarity for IC307. Resistors R316 to R323 and R343 to R350 reduce the
amplitude of the control signals to 2.5 V. The outputs of IC307 are converted from ECL to TTL
levels by differential pair TR302 and TR303 and a single-ended amplifier TR304. Diode D307
provides Schottky clamping for TR304 to ensure fast switching. The signal on the collector of
TR304 is an all active edge squarewave at a 2.5 MHz rate. The fractional control ASIC and phase
detector both require a clock with active positive edges. IC310d converts the 2.5 MHz signal to a
5 MHz signal with a short duty cycle and an active positive edge. The remaining gates of IC310
provide buffering. The division ratio generated by ASIC IC305 will be modified every time a
positive edge is received at pin 51.

The reference for the main loop is obtained by dividing the 25 MHz signal present at IC302 pin 2
by five. The output of IC302 pin 11 is a 5 MHz rate pulse with a duty cycle of 40 ns. The clock
for the 1-bit oversampled A-D converter is obtained from IC302 pin 13 after buffering and
inversion by IC303a. The reference and divided output signal are compared by a phase frequency
comparator comprising IC311, IC312b and IC313a. The phase detector output to the loop
integrator and filter is available on pin 12 of IC311d. Under normal phase lock this will be a
5 MHz squarewave with nearly 50% duty cycle.

TECHNICAL DESCRIPTION

1-bit A-D converter

The DC input path to the Synthesizer consists of a third-order, single-bit, oversampling A-D
converter, whose bit stream output is used to dynamically control the Synthesizer frequency via
the Synthesizer ASIC.

46882-377 1-9

TECHNICAL DESCRIPTION

Pin 6 of IC301b is used as the summing junction for four currents. These are: the input current
from control board AB1 or AB1/1 via R307 and R352; a negative offset current via R306; the bit
stream feedback via R310; and the DC nulling offset current via R311. IC301b integrates the sum
of these currents, and its output is further integrated by broken integrators IC301c and d. In these,
when the frequency rises to a point where C301 and C302 are at low impedance, the ICs act as
unity-gain amplifiers. Diodes D301 to D304 are used to enable the converter to recover cleanly
from an overload.

The output from the last integrator is fed via comparator TR301, which converts the input to TTL
levels, to D-latch IC304a, which is clocked at the same rate as the Synthesizer ASIC. The output
from the D-latch is fed back into the summing junction to close the converter control loop. The
output from IC304a is a pseudo random bit stream that represents the analogue FM input to
IC301b. The bit stream is used by the Synthesizer ASIC to control the main carrier frequency.

BIPOLAR

OFFSET

FM/FM

DC

NULLING

OFFSET

S

5 MHz

1-BIT
ADC

CONTROL

DATA

FRACTIONAL

CONTROLLER

CLK

FROM
VCXO

25 MHz

REF

DIV

5¸

DIVIDE

BY N

COUNTER

600-1200 MHz (AA1)
600-1255 MHz (AA1/1)

MHz

FN

LOOP

HIGH

WINDOW

COMPARATOR

5 MHz

2.5

x2

5 MHz

2¸

1.2-2.4 GHz (AA1)

1.2-2.51 GHz (AA1/1)

FM ATTEN

VCO

PRE- STEER

VCO TUNE HIGH

HARMONIC

GENERATOR

S

VCO

VCO

TUNE

LOW

FN

LOOP

LOW

C4438

Fig. 1-3 Frequency synthesis

The DC nulling offset current is supplied from a 1-bit oversampling D-A converter in the
Synthesizer ASIC. This balances the input current to make the converter read zero when DC
nulling and when in AC coupled FM mode.

RF board: Loop filter and autocal (sheet 4)

Loop filter

The input on the PHASE DETECTOR line is filtered by R404 and C401 to remove fast edges
before the signal reaches loop integrator IC402. The loop integrator has a break frequency set by
C402 of approximately 1.5 kHz and gain at high frequency of 1.2. The network R414, R415,
C405 and C406 provides rejection of unwanted noise in the 10 to 30 kHz range without
introducing a large phase shift at the loop bandwidth. IC404 is a unity gain second-order active
low-pass filter with a cut-off frequency of 40 kHz. The filtered signal from IC404 is attenuated
and summed with the FM drive signal on the FM ATTEN line by R433. This results in the VCO
TUNE LOW output to the VCO (sheet 1). Loop bandwidth is approximately 3 kHz.

1-10 46882-377

Correct phase lock is monitored by IC406c and d which detect when the voltage at the output of
IC406a exceeds ±8 V. Hysteresis is provided by R443 and R444. The detected outputs from
D408 and D409 on the FN LOOP HIGH and FN LOOP LOW lines are attenuated to logic levels
by R449 to R452. Loss of phase lock is signaled by interrupting the main processor via IC703 and
IC704 (sheet 8).

VCO pre-steer

The VCO PRE-STEER voltage is generated by octal DAC IC103 (sheet 1). The signal from the
DAC is amplified by IC401a and b to provide a tuning voltage in the range 1 to 22 V.
Temperature compensation for the VCO is provided by D414. Under normal operation the pre­steer voltage is filtered by R423 and C411 to prevent noise injection onto the VCO tune line.
Diode D415 and IC408 allow fast tuning by shorting out R423 to reduce the charging time
constant. IC408 is only switched on using the PRE-STEER SWITCH line during frequency
changes that involve updating the pre-steer voltage.

Autocalibration

Dedicated hardware has been added to the Synthesizer to allow fast automatic calibration of the
VCO pre-steer and FM frequency response. Pre-steer calibration is achieved by minimizing the
loop error voltage present at the output of IC406a. This is achieved by IC406b which forms a
simple zero-crossing detector.

The FM frequency response calibration is performed by applying FM to the carrier with a 2 kHz
modulating tone. Calibration is performed by minimizing the amplitude of the resulting 2 kHz
tone present at the output of the loop filter. The magnitude of the FM drive voltage applied to the
VCO is adjusted automatically whilst the phase relationship between the loop error tone and the
applied modulating tone is monitored. The correct drive level is found at the point where the
phase switches from being in phase to being out of phase. IC407a is used to amplify the loop
error tone. TR402 and C417 are used to implement a crude charge pump phase detector. IC407d
is used to clip the 2 kHz modulating tone so that TR402 gate is driven with a squarewave. The
output from the phase detector is filtered by two RC sections and buffered by IC407b. The sign of
the filtered voltage, and hence the point of phase reversal is monitored by IC407c. The output of
IC407c is converted to logic levels by D412, R457 and R458. Forward biasing D404, D405,
D411 and D413 using the CAL DISABLE line suppresses the operation of the autocalibration
hardware.

TECHNICAL DESCRIPTION

AA2 board identification

The AA2 BOARD SENSE line indicates one of three conditions to the processor: a standard
attenuator board AA2 is fitted; a high-power attenuator board AA2/1 is fitted ; no attenuator is
fitted. PLAE 15 indicates these conditions respectively by being: shorted to earth; open circuit;
connected to earth via a 1 kΩ resistor. The two output lines BOARD ID (A) and BOARD ID (B)
are connected by pull-up resistors R723 and R724 to IC705 (sheet 8). The logic is shown in Table
1-2. below.

BOARD ID

Board type PLAE 15 TR406 TR407 (A) (B)

Standard Shorted to

High power Open circuit ON ON L L
No attenuator Resistor ON OFF L H

Table 1-2: Attenuator board identification

OFF OFF H H

earth

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