Kenwood PF-810 Service manual

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FUNCTIONPOWERMETER

PF-810

OPERATING INSTRUCTIONS

CONTENTS

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . 3

Features.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Specifications.. . . . . . . . . . . . . . . . . . . . . . . . . 4

Principlesofoperation.. . . . . . . . . . . . . . . . . . . 5

Operatingparts. . . . . . . . . . . . . . . . . . . . . . . . 7

Cautions. .. . . . . . . . . . . . . . . . . . . . . . . . . . 9

Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Schematicdiagram. . . . . . . . . . . . . . . . . . . . . . 12

Smithchart. . . . . . . . . . . . . . . . . . . . . . . . . . 13

Applications.. . . . . . . . . . . . . . . . . . . . . . . . . 14

INTRODUCTION

The Function Power Meter ModelPF-810isa passing

type power/SWR meter coveringa wide frequency range of 1.8MHzto 200MHz. It isa laboratory quality, profes-

sional instrument for observing and measuringforward

power from transmitter to load (antenna) and reflection power from load to transmitter.

It is also capable of measuring power actually con-

sumed in load (forward power minus reflection power)

for convenience of checking the conditions of trans-

mitter and load, in addition to measuringSWRat power greater than 1W.

Besides being used to monitor the operating condi- tions of transmitter or to adjust filters, matching circuit, etc., it is also used to monitor production lines and businessuse radio stations.

--"---"" ,.~ ~

FEATURES

* Troidal core type directional coupler assures flat fre-

quency response, eliminating the need for calibration tables; calculations and handling knob of frequency variation.

* Frequencies are practically flat over the range of 1.8

MHz to 200MHz in full scale of meter even in 1.9MHz or 3.5MHz band, thus permitting measurements of

various functions in low bands with small power.

* Radiant power (RAD) indicator (Pat. pending) to in-

dicate forward power minus refrection power, is included in the instrument. This is particularly useful to prevent trouble which might occur during matching work, and facilitates monitoring and adjustments of

transm itter.

* Aritenna selector switch is self-contained to select

either of two antennas for quick QSY. If a dummy

load is connected instead of antenna, the instrument

functions as a terminal type power meter.

* Large sized, linear scale for easy and error-free read

ing of SWR and power.

SPECIFICATIONS

Measurement items:

Frequency range:

Power measurement

range:

Range setting: SWR measurement

range:

Minimum power for

SWR measurement:

Power measurement

accuracy:

Residual SWR: Frequency response: Insertion Loss:

Type of connector:

Input/output

impedance:

Output terminal:

Forward power, refrection power, radiant power and SWR

1.8MHzto 200MHz

1Wto 150W 5W, 25W and 150W(3 ranges)

1.0 to 10

Within :t10% of full scale

Less than 1.2

Within :t 0.25dB

Less than 0.5dB "UHF" type

50-ohm

Two (selected by pushbutton

switch)

J..

j,,,

I I

PRINCIPLES of OPERATION

The Model PF-810 is composed of four major units, a directional coupler, a voltage converter, an indicator and a switching unit; all units except the antenna selector and the directional coupler, function as a DC circuit.

Directional coupler

The directional coupler is used to pick up a very small

power from the coaxial cable connected between trans- mitter and load by separating forward wave and refrec-

tion wave components.

The directional coupler used in PF-810 consists of a wide band current transformer T1 and a voltage trans- former T2, both employing troidal cores as shown in

Fig. 1.

Rfwd

"-- i3

Fig. 1

"")

i4 '$ Rref

ANT

1 In Fig. 1, suppose that a current "il" flows from TX to ANT, then a reverse current "i2" flows into the secondary of the current transformer T2. At this time, a current "i3" is flowing into the primary of the voltage

transformer and, hence, a current "i4" (=i2/2) developed from "i2" and a current "i5" developed from "i3" to- gether flow into the secondary of the transformer.

If these two currents (i4 and i5) are equal, no voltage

appears across "Rref" because the currents flowing into

"Rref" in reverse direction each other are cancelled, however, a voltage appears across "Rfwd" because the

currents flowing into "Rfwd" have the same directivity.

If power is refrected by ANT, the current "i5" con-

tinues to flow in the same direction, while the current

"i4" flows in reverse direction, thus a voltage appears

across "Rref", too. Such an action is independent of frequencies if T1 and T2 each ahve a wide frequency

band.

The directional coupler of PF-810 uses wide band transformers constructed with troidal core and newly developed windings, to pick up the diode detected voltage, proportional to forward power and refrection power, from the resistors of "Rfwd" and "Rref".

Voltage converter

The voltage converter is used to provide linear read- ings of power on the scale. Without this converter, the DC voltage from the directional coupler, which is pro- portional to forward power or refrection power, is proportioned to the square root of power, thus the

readings on the scale are crowded which causes dif-

ficulty in reading or loss of reading accuracy.

The voltage converter uses specially selected diodes, resistors and capacitors. The same type of converter is connected to both the forward power and refrection

power terminals. Indication and selection

The voltage signal from the voltage converter, which is proportional to power, is indicated on the 100,uA DC ammeter through the function selector switch. The power range is selected by the range selector resistors. Two sets of voltage converter and selector of the same design are provided for forward power and refrection

power. These can be used simultaneously. Being so

designed, PF-810 is able to indicate radiant power(RAD). This is achieved by the differential operation of the voltage converters to wh ich forward and refrection wave voltages applied respectively.

In PF-810, two identical circuits are connected back to back to further improve the performance of the directional coupler.

I J;

V.FWD

V.REF

Fig. 2

ANT

ANT1

() () ANT2

...

.;;'

fig. ~ olock Diagram

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