•High gain - 20 dB Broadband coverage.
•Excellent review in Feb. 90, 73 Magazine.
•Two stage feedback design ensures stable operation.
•Runs on 12-15 VDC @ 15 mA.
•Complete with applications and hook-up instructions.
BROADBAND RF PREAMP
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100 KHz - 1.3 GHz
Perk up that old receiver! Great for scanners, TV sets, frequency counters, shortwave sets, anywhere a stable 20 dB gain is needed!
SA7—1 |
Kit No. SA7 |
SA7 INTRODUCTION:
A "preamplifier" gives an initial boost, measured in decibels, to the level of a signal before it is processed by tuned circuits, filters, amplifiers, mixers, detectors or other circuit stages. Preamps may be designed for either RF or audio use and may be either tuned or broadbanded. The SA7 is indeed a "general purpose" RF pre-amplifier. While we realize that most users understand the term "broadband", we understand that some of you would appreciate some clarification. In short, "broadband" means you can use the SA7 to boost the RF level of any signal from the AM broadcast band through VHF and UHF FM and TV bands all the way into the 1300 MHz microwave spectrum. This is possible because the SA7 does not limit or restrict the RF input by means of tuned circuits or filters. Therefore, ALL signals reaching the input are amplified equally. This amplifier differs from the Ramsey PR-10, 20 and 40 models for 144 MHz, 220 and 440 MHz respectively, in that those models include hi-Q tuned circuits to "pre-select" the desired frequency range, restricting the strength of other signals, out of band. A "pre-selector" is a pre-amplifier with a tuned input. We'll show you how to use the SA7 as the heart of such a pre-selector configuration, either fixed or tunable, if that is the practical application which is of most interest to you. So,"broadband" is a mixture of good news and bad news, though it's mostly good news if you understand what such a circuit can and cannot do. Because it boosts all signals equally, its successful operation relies on the input tuned-circuit selectivity of the receiver whose performance you wish to boost. If the receiver does not have much ability to reject unwanted signals, such signals will be boosted just as much as the desired signal.
SA7—2
PARTS SUPPLIED WITH SA7 KIT
Capacitors
1 2.2 pF capacitor [axial style, green body with red bands] (C6)
1 4.7 or 5 pF disc capacitor (C1)
3 .01 uF disc [marked .01 or 103 or 10 nF] (C2,3,5)
1 4.7 to 10 uF electrolytic capacitor (C4)
Resistors
1 47 ohm SMT (surface mount technology)"chip" resistor (R6)
1 51 ohm [green-brown-black] (R2)
2 100 ohm [brown-black-brown] (R1,R5)
1 470 ohm [yellow-violet-brown] (R3)
1 1K ohm [brown-black-red] (R4)
Special Components, Semiconductors:
1 SA7 printed circuit board
1 .04 uH coil [4 turns pre-wound] (L1)
2 2SC2498 or 2SC2570A microwave bipolar transistor (Q1,Q2)
SA7—3
REQUIRED, NOT SUPPLIED
8-15 VDC power source
your choice of power on-off switching
RF input and output connectors (your choice of type)
enclosure of your choice, if SA7 is not mounted inside receiver or counter, etc.
SA7 layout
SA7—4
SA7 PRE-AMP ASSEMBLY PROCEDURE
Soldering 15 parts to a PC board is not a big job, but good performance of the SA7 requires attention to keeping all leads as short and neat as possible. The order of the parts installation is not critical for this and other small kits, so the purpose of following the suggested order of assembly is just to make it as easy as possible for you to get the right parts in the right holes. By the time you build your fourth or fifth SA7 for your neighbors old shortwave set or your aunt's FM radio, you'll be an honorary member of the Ramsey factory assembly line! In working with a small PC board such as the SA7, a miniature vise plus a magnifier may prove very helpful.
STEP-BY-STEP PC BOARD ASSEMBLY:
In all steps below, the word install means to insert the component, oriented correctly, into the right holes, solder all wires and cut or nip away excess wire flush with the solder connection.
1. Install R1, 100 ohms (brown-black-brown).
2. Install R2, 51 ohms (green-brown-black).
3. Install C1, 4.7 or 5 pF.
4. Install C2, .01 uF (marked .01 or 103 or 10 nF).
SA7—5
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