Yaesu FRG-7

[tiv48]

one for the sets data base will upload manual later
rob t

[Skywave]

Rob - you have a PM.

Al.

[Skywave]

Hi Rob,

Manual now downloaded & stored: thank you.
Incidentally, you have a PM.

Al. / June 15 //

[Skywave]

The Yaesu-Musen receiver, model FRG-7: a report.

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Introduction.

In the short-wave listener and Amateur Radio world, this receiver is somewhat affectionately known as a “Frog 7”. From memory (so don’t quote me on this! ), it was in wide circulation, as new, in the mid-1980s, when, generally speaking, it received many favourable reports and reviews from satisfied users. And, it would appear, there are many in use today. The purpose of this report is simply to acquaint those who are not familiar with this receiver and its main features and perhaps thinking of acquiring one (they frequently appear on e-bay, for example), or to remove some of the mystery associated with its tuning system.

This receiver is a ‘solid-state’ synthesized communications receiver covering the radio spectrum from 500 kHz to 30 MHz without any gaps. It is a triple-conversion superhet, using the famous ‘Wadley loop’ (as first manifest in the famous Racal RA-17 receiver ). One of the main benefits of this system is the automatic cancellation of frequency drift in the manually-tuneable first VFO.. The other main benefit is the ability to cover a wide frequency range without gaps: in fact, it is the choice of the final I.F. that predominately dictates the lowest freq. that the receiver will actually tune down to. In the case of the FRG-7, this is 455 kHz. (In the RA-17, it is 100 kHz).

To the uninitiated, the front panel’s controls look somewhat bewildering - they are certainly not conventional as regards a ‘run-of-the-mill’ communications receiver - but that is simply because the user controls are a reflection of the Wadley Loop system that is used. Now although any user can (theoretically) simply follow the user’s handbook to successfully operate this receiver and without any idea of ‘what’s happening under the hood’, an understanding of the basic principles involved in the Wadley Loop System makes for a better use of the controls. An outline of this System now follows.

A variable capacity-tuned VFO tunes from 55.5 → 84.5 MHz. Its output is fed two ways:
1. To a mixer, whose other input is the aerial input signals in the freq. range 0.5 → 30 MHz. The resultant I.F. from this mixer will be a spectrum of signals, 1 MHz wide, from 54.5 → 55.5 MHz.
2. To another mixer, whose other input is a comb of signals, 1 MHz apart, in the range 3 → 32 MHz. These signals are initially generated in a 1 MHz crystal oscillator and fed to a harmonic generator: this producing the comb of frequencies at 1 MHz intervals. The output of this mixer is fed to a filter that rejects all the products from this mixer except the one at 52.5 MHz.

The resultant I.F., 54.5 → 55.5 MHz, (from section 1 above), is fed into yet another mixer whose other input is the 52.5 MHz. from section 2 above. Hence, the output from this last mixer will be a spectrum of signals from 3 → 2 MHz, corresponding to any 1 MHz ‘chunk’ in the input R.F. spectrum, 0.5 → 30 MHz.
And that, in essence, is the Wadley Loop triple-mix system. It is because of the ‘arithmetic’ that is used in the 3 mixers in conjunction with a 1 MHz crystal oscillator that any frequency drift in the VFO (55.5 → 84.5 MHz) is cancelled out as far as the resultant signal is concerned at the 3 → 2 MHz range.

The resultant spectrum, 3 → 2 MHz, is now simply converted into the final I.F. of 455 kHz by using a conventional capacity-adjusted VFO. The rest of the set broadly follows conventional comms. receiver practice: a chain of I.F. amplifiers, selectable detectors for A.M. or SSB / CW, AGC generation and an audio amplifier driving an internal speaker mounted on the front panel, S-meter, etc. It is powered from conventional a.c. power (110v → 230v) or internal or external batteries. .

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As far as the operator is concerned, what the above-mentioned tuning system amounts to is one of selecting the band of interest using the BAND switch, adjusting the MHz dial for the appropriate ‘MHz’ setting, adjusting the’ preselector tuning’ to the approx. freq. of interest, and tuning over a 1 MHz spectrum using the main tuning dial (kHz) with its knob. Oh, yes – and selecting the various other features – detector (AM / SSB), attenuator switch, volume control – all conventional stuff, more or less. As you can now see, this ‘tuning in a station’ procedure is not the usual we expect to find in an ordinary radio: ‘domestic’ or ‘comms.’ type. As someone once said, “Most s/w and comms. receivers you simply ‘operate’; you have to drive a Frog 7”

The design has a few ‘extras’ thrown in, some of which I found to be of dubious / doubtful worth. There is a choice of aerial connections on the chassis backdrop (useful); there is a front panel mounted LED to tell the user when the first VFO is set incorrectly: a LED goes red.: again, useful. (More on this later). There is only one conventional ‘gain’ control: A.F. gain. Agreed, there is a sensitivity / attenuator switch marked “DX, NORM., LOCAL”, but I would have been far happier with an additional and separate I.F. gain control brought out as well (a-la the RA-17). Ah, yes: you can switch the dial lights off. (Why? You cannot see the tuning dials if you do this – and they’re not brilliantly illuminated in the first place! ). But the most really confusing (and annoying) ‘feature’ must be the way Y-M have arranged the tuning on the two lowest frequency bands: band A = 0.5 → 1.6 MHz and band B = 1.6 → 4.0 MHz). What all that amounts to is that for Band A, 0.5 → 1.0 MHz, only the ‘top half’ of the main tuning dial is used: so the ‘MHz tuning’ will be set at zero. For 1.0 → 2.0 MHz, the MHz dial will be set at 1 and the whole range will be tuned over all of the main dial. Ditto with Band B: the section 1.6 MHz to 2.0 MHz occupies only the ‘top half’ of the main tuning dial. The manual does attempt to explain all this, but I found it difficult to comprehend. It was on account of my knowledge of the RA-17 that I was eventually able to figure it all out myself. (I documented my analysis for these two bands in a M-S ‘Word’ document for future reference: contact me if you would like a copy.)

Now in fairness to Y-M, there may be good reasons for this obscurity: Racal manage to do it all in simple 1 MHz steps: perhaps there was a patent issue; perhaps I need to study the ‘arithmetic’ of the Wadley Loop process (as used here) in more detail. However, my experience of Y-M’s products over the years has led me to conclude that they have a nasty habit of not quite ‘finishing off’ their products prior to release and also fitting features of doubtful value at the expense of more useful ones. (I own a Yaesu-Musen FR-50B that has been much modified). I suspect that the cultural differences between East and West account for some of this. However, most of that is not engineering fact: merely my opinion.

What is not opinion, but is engineering fact, is the overall assembly and mechanical design. As is typical of receivers from the Far East of this vintage, the bulk of the electronics is assembled on two pcbs: the RF board and the IF/AF board. As far as maintenance is concerned, there will be problems. Not only are the components really crammed onto these two boards (again, conventional Far East style) but also many of the active components will almost certainly be impossible to obtain now. On the other hand, the reported reliability of these receivers is very good. And that is just as well, since as with the Racal RA-17, a complete realignment is not a trivial undertaking. The two problems I met on mine were that the flexible couplers on the shafts of the MHz preselector and MHz tuning capacitors were split – rendering the preselector and ‘MHz’ tuning as non-functional. These couplers were simply replaced and the necessary adjustments carried out. The ‘KHz’ tuning dial was about 100 kHz out. Again, a simple redo of the tracking of the associated oscillator fixed that.

The one feature that I found irritating – and that I could easily do something about – was the MHz ‘LOCK’ LED on the front panel. By design, when the MHz VFO is ‘in lock’, the LED is extinguished; when it’s red – the VFO is out of lock. Now I find it disconcerting to have an active warning when something is ‘wrong’ and a passive indication when something is ‘O.K.’ :s So a simple mod. was incorporated using a bi-colour LED: green for ‘in lock’; red for ‘out of lock’. And I found that this simple mod produced a much more ‘comfortable’ feel when operating this receiver. Psychological it may be, but ergonomics are important in operating a piece of kit like a complicated comms. receiver. (Note: the choice of colour for the front panel of the RA-17 was deliberate. The chosen colour was that which was found to produce the least amount of ‘eye fatigue’ for the operators – who could be at their receivers for as many as eight hours at a time, frequently more).

There are almost certainly areas of interest and features in this receiver that I have made no reference to in the above. (This report has extended to a length that has far exceeded by expectations!) And I am yet to carry out any electronic performance measurements on this receiver – although I noted, when quickly checking it ‘by ear’ using an HP 8640B sig. gen., that the apparent sensitivity left little to be desired. If anyone (who successfully managed to wade through that lot above) has any questions to ask about this receiver, or the Wadley Loop tuning system in general, I’ll be happy to help where I can.

In the pictures below, the small Veroboard pcb under the chassis is my mod. for the “MHz tuning LOCK” bi-colour LED.

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Al. / June 2011 //

[AlanBeckett]

Al,
As you know I worked for Plesseyin the late '60s and early '70s. I also had dealings with Racal. The simplest thing that I can say, without upsetting anyone or violating the various Official Secrets Acts, is that they were Professionals, and the Taxpayer chucked an awful lot of money at them.
Of course, the actual gear didn't get onto the open market for a long time, in fact long after the profesional kit used by the Military had moved on.
Alan