A hot little amplifier at an extremely low price
Ramsey Electronics 793 Canning Parkway Victor NY 14564 (716) 924-4560 Pnce Class: $15.00
The SA-7, new from Ramsey Electronics, is an easy-lo-build kit for a generat purpose broadband RF amplifier, capable of operating from 100 kHz to 1 GHz. it1s small on price, but big on performance.
After searching high and low (no pun intended) for an inexpensive preamp lo help boost the front end of a tired shortwave communications receiver, I came across the Ramsey Electronics advertisement announcing several nev^ mini-kits The SA-7 preamp M was inexpensive, so I took the plunge and ordered it. One week and $15,00 later, I received a curiously small parcel from Ramsey.
The SA-7 is easy to assemble Tiere are only 15 components to mount on a phenolic circuit board measuring 1W x I put it together in about 15 minutes using just a soldering iron, a steady hand, and about an inch of solder You won't need to use any tuning or test equipment after completion Even a firsttime kit builder can tackle this project with confidence.
But, even as a "veteran" kit builder, I almost forgot to mstatl the kit's only SMT (surface mount technology) resistor. After assembling and soldering all the components on the PC board, you must solder the SMT resistor between the two designated foil traces on the foil side of the board. Remember also to keep all of the other component leads as short as possible if you want to exploit the amplifier's capabilities on the "high end ' of its range. Long component leads may also cause it to break into oscillation.
After mounting the SA-7 within an Allied AX-190 receiver, t put in a jumper within the receiver's power supply and borrowed approximately 9 volts to run the newly installed
amp Current drain is minimal (less than 50 mA) and the power requirement for this amp is 8 to 15 volls DC. Since this voltage is available in most solid-state equipment, it's a snap to use the available power already present within the gear. The extra current dram usually won't be noticed. If you opt to use the SA-7 in a tube ng, a 9 volt battery or an outboard power supply woutd be an alternative solution.
After turning on the receiver with the SA-7 in line, t was pleasantJy surprised to notice a marked increase in the number of stations on the air. 1 noted a solid two S Unit jump in signal Strength throughout the HF receiver's range. Stations barely audible wtth the SA-7 oui of line came up to "armchair copy" when the amp was put between the antenna and receiver. I noted an increase in the noise floor but ihe two-plus S Unit increase in received stations1 signal strength more than compensated for the associated and expected increase in the receiver's noise floor The spec sheet indicated a 3 to 5 dB noise figure.
When preamplifiers are added lo a receiver, images and heterodynes may appear, espe cially if the preamps don't have selective filtering as part of their design. At VHF and UHF frequencies, images can become a real prob* lem when the receiver and antenna are located near crowded RF environments Some preamps may end up acting like broadband mixers I didn't notice this with the SA-7, but it could become a problem.
The design of the SA-7 is simple and straightforward, and the addition of helical fillers or tuned circuits would totally defeat the idea of keeping this kit under the $15.00 mark. This amplifier contains two stages (with no tuned elements); a common emitter stage which drives an emitter-follower by utilizing two 2SC 2570s. Page 17 of the ARRL publication, Hmts and Kinks for the Radio Amateur, circa 1975, described a similar circuit design as a "general purpose preamp." This publication stated that a common emitter-follower stage tends to be unstable DuL as explained in the Handbook, the absence of tuned elements allows tor extremely good stability.
listed specifications claim a gain of 15 dB at 1 to 950 MHz and 8 dBai 1300 MHz TheSA^7 can be used in many applications requiring extra gain in a wide variety of amateur and general coverage receivers. It can also be used to increase the sensitivity of frequency counters. Because of its small size, the SA-7 can be used internally in almost all receivers, or placed in a small chassis, for a variety of applications within the hamshack.
On a scale of 1 to 10 (nof/r? I would give this little broadband RF amp a 10!! NowT I wonder if the SA-7 would work in boosting the horsepower in my Ford Ranger?1? H
Contact Dave Pelaez AH2AR/B at 4872 Trail* side Court, HuOer Heights OH 45424,
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