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YAESU MUSEN FRG-7


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The FRG-7 is a communications receiver produced by Yaesu Musen of Japan from 1977 to 1980. Earlier units were sold in Europe under the Sommerkamp label. The FRG-7 is completely solid-state and uses the famous Wadley Loop circuit to stabilize the frequency. A coarse tuning knob selects one of thirty 1-MHz-wide bands and a single 1 MHz crystal provides the necessary spectrum of harmonics to lock the receiver. Fine tuning within the band is achieved by a standard Local Oscillator with a drum dial calibrated every 10 kHz. Unfortunately the tuning scale is not linear and not very accurate, so deviations of 5-10 kHz are present except at the endpoints, which can be calibrated using the 1 MHz harmonics. As in all Wadely Loop receivers the design is triple-conversion, with the last IF at 455 kHz.

The FRG-7 circuits is straightforward but used fairly advanced components for its time, with various MOSFETs and FETs in critical areas. An IC balanced mixer is used in the loop circuit. A tunable preselector (four bands) allows to peak the receviver and helps in rejecting interference. Overloading can be reduced by a manual attenuator on the antenna input. There is a product detector for CW/SSB. I can't really judge its quality since I never used the FRG-7 for SSB reception. The receiver is extremely stable, has good overload characteristics and delivers a pleasant audio. Unfortunately the selectivity is broad (6 kHz) therefore I installed a special IF narrow filter (Murata CFS-455-I) which was sold in a kit by Gilfer Shortwave to improve selectivity.

The FRG-7 outperformed all the similar solid-state Wadley Loop receivers of the epoch, namely the Drake SSR-1, the Realistic DX-300, the Standard C-6500 and the Barlow Wadley XCR-30 (here the comparison is a bit unfair since the XCR-30 was a portable radio.) It was replaced in 1980 by the FRG-7000 which had a digital frequency readout. Gilfer Shortwave and Radio West in the USA sold two modified versions with improved selectivity. Gilfer also produced a kit to replace the original IF ceramic filter with better quality one (see picture below.)
I purchased my FRG-7 in 1979 and during 15 years it was my main DX-ing receiver, until I purchased a Kenwood R-5000. It is still in excellent shape and also the Wadley Loop circuit performs flawlessly. I should perhaps check the calibration but since it requires some sophisticated equipment I always postponed this chore.

Bands

Charateristics

Controls

30 bands 1 MHz wide
from 0.5 to 30 MHz

Preselector bands
  • A 550-1600 kHz
  • B 1.6 - 4.8 MHz
  • C 4.8 - 14.5 MHz
  • D 10.3 - 30 MHz
  • 4 MOSFETs
  • 2 FETs
  • 2 ICs
  • 1-MHz crystal
  • 1st IF: 54.5-55.5 MHz
  • 2nd IF: 2-3 MHz tunable
  • 3rd IF: 455 kHz with ceramic IF filter
  • Antenna input: 50 ohm and high-impedance
  • 455 kHz IF ceramic filter
  • MHz tuning
  • Lock indicator LED
  • Main Tuning
  • Fine tuning (later models)
  • Dial set (calibrator)
  • Preselector band switch
  • Preselector tuning
  • Antenna attenuator switch
  • Tone switch
  • Mode switch (AM/CW/SSB)
  • Dial light switch
  • Power switch
Dimensions and weight: 15 cm high, 34 cm wide, 30 cm deep. Weight: 7 kg
Power requirements: 100-234 VAC, or 12 VDC (external battery or internal cells)

FRG-7 operating manual (BAMA site)


Go to G3YNH page The venerable predecessor of the FRG-7: with its 23 tubes and 31 kg weight the RACAL RA17 was a true Boat Anchor.
Click for larger image The Barlow-Wadley XCR-30 was the first solid-state receiver employing the Wadley Loop principle. Introduced in 1976 it was a hit in the SWL market. Unfortunately it disappeared few years later. It has still many fans all over the world. Here the XCR-30 appears on the cover of the 1977 World Radio TV Handbook, the SWL's bible.
Click for larger image The Drake SSR-1 was introduced in 1976. A cheap and poor-performing receiver, it was not in line with the great Drake tradition. It was a market failure. The picture depicts an ad from the italian magazine CQ Elettronica.
Click for larger image Inside view of the chassis seen from above. The construction is very solid and high-quality. Clockwise from top left: (a) PC board with the tunable 2nd IF (2-3 MHz) plus 3rd IF and AF circuits; (b) the cylindrical drum of the main tuning dial; (c) preselector tuning and MHz tuning controls; (d) 1st IF strip (54.5 - 55.5 MHz); (e) power supply transformer.
Click for larger image Bottom view of the 3rd IF strip board. The Murata 455 kHz ceramic filter comes from an add-on kit by Gilfer Shortwave and was added to improve selectivity. According to Gilfer the nose bandwidth is 4 kHz and 10 kHz @ -60 dB (instead of 6/20 kHz of the original LF-6C)
Click for larger image Foreground: the tuning capacitor of the preselector circuit. Behind it is the MHz tuning capacitor with the 55.5-84.5 MHz VFO board mounted directly on the top. Two 90-deg angle gear drives actuate the drum dials. The PC board above the drums holds the dial lamps. These lamps are really longlife. Only one failed in my set after more than 20 years. I did not bother to look for a replacement (presumably very difficult to obtain) and I put at its place a bright white LED with a suitable dropping resistor (I don't remember the value). It is virtually impossible to distinguish between LED and lamp.
Click for larger image The drum dial of the main tuning control. The scale is unfortunately not a linear one, but a Linear Master Oscillator like those of a Collins or Drake would have added a lot to the cost. My scale is not very precise an it needs be calibrated at both ends. When properly set one can read the frequency within 5 kHz. Partially hidden is the small fine tuning capacitor that is very useful to tune in SSB signals. Early FRG-7 models did not have this control.
Click for larger image The FRG-7 seen from the back. The rectangular snap-on cover on the left allows access to the optional internal battery holder for portable use.

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