FRG-7. Very quiet

[Jon_G4MDC]

I can very well understand the point about preselector overlap.

What does a dual colour lock LED achieve plz?

[Restoration73]

Lock indication is more like a bistable ;

http://www.monitor.co.uk/radio-mods/...en-led-mod.htm

It should be noted the lock led indicator is more prominent on the FRG-7000 receiver.

[Radio Wrangler]

Careful!

This is a Wadley front-end. There is no locking going on at all. Despite most people calling it a loop, there isn't even a loop!

The incoming signal is mixed up to a high IF near 40MHz using a free-running VFO.

It is then mixed down to a 2 to 3 MHz IF using an LO made by mixing that same VFO with a 1MHz comb spectrum (from a crystal oscillator) and filtering the wanted product.

This is a brilliant trick and if the VFO drifts a bit, the first signal mixer shifts the signal in the high IF a bit, but the LO for the second signal mixer gets an LO signal that moves by the same amount and cancels the drift.

It sounds like magic.

The stability comes from the crystal oscillator/comb generator.

As you tune the Wadley VFO it feels like you have a receiver receiving a group of frequencies all at 1MHz steps, and as you turn the knob, one frequency fades out as the next one, precisely 1MHz fades up.

So anyone saying "Wadley loop" doesn't understand the system. Ditto '"Lock" (And that includes Yaesu themselves!)

The Racal receivers had no indication other than the dial markings for where to put the VFO tuning to get a specific MHz.

The Frog-7 has an LED to show when the LO for the second signal mixer has climbed the skirt of its filter.

David

[Jon_G4MDC]

Guilty as charged. Sloppy terminology.

I don't know what Yaesu called that LED but anyway I still want to know if it's doing anything!

[Radio Wrangler]

As the 2-3MHz receiver sections tune 1MHz, and you don't want to have to change the 'MHz' oscillator, the high IF needs to have a filter which passes signals +/- 500kHz with respect to nominal, but reject signals that would be at any of the images of the subsequent mixer. This is a tight-ish requirement for a filter, but the one in the LO path is harder.

The Racal sets never had any indicators at all, yet the government employed ordinary signals people to use them. THe tuning markings on the MHz dial are accurate enough so you hit the right megahertz transposition, so an eyeball will get you going and hearing something even if just noise. A vernier tweak of the MHz knob will peak it up and away you go, tune around with the kHz knob.

The set hinges on those filters. The Racal ones are famously a right b*gger to adjust and people have put sets out of action trying. You need some experience or some guidance and a sweeper. THe Yaesu ones are rather simpler, but no easier to adjust, and the result isn't so flat-topped. So having a peak of the MHz know for max response is worth doing if you move far on the kHz dial.

So, you don't need the LED, but it's a comfort blanket for getting some people going.

Unfortunately Yaesu wrote "Lock" on the panel by that LED and it's been leading people astray ever since. Add in the common (but wrong) term Wadley loop and absolute confusion reigns!

David

[Jon_G4MDC]

I thought I would take a look at the manual - never having owned one of these receivers.
They certainly describe the working of it in the wrong way.

"The LOCK lamp lights up when the synthesised heterodyne oscillator is unlocked."

I reckon that's a copy/paste error from the manual writing department. They probably weren't fed enough information (very common) - work it out for yourselves. Synthesised - nope. Unlocked - nope. Off tune - well yes.

Just hoping to keep the thread alive until the OP can come back and tell us some more. It's a set I thought about buying, back in the day, but I never did.
Maybe I need one now, just to see if they are any good.

I have been thinking about how it would work with the HF(Bandset) LO phase noise vis-a-vis a synthesiser. Might it cancel through the different mixing routes?
As there are two different BW filters in the mixing paths there are 2 different delays - maybe this gets rather off topic.

[Julesomega]

My guess is there's 2 random noises of the same spectrum added together so will give 6dB worse (phase)noise

[Radio Wrangler]

Originally Posted by Julesomega

My guess is there's 2 random noises of the same spectrum added together so will give 6dB worse (phase)noise

Not quite. Phase noise gets into both front end mixers from the MHz VFO and almost cancels. There is the small matter of the group delay of the LO side filter, so the cancelled phase noise is just slightly wrong in time.

A wadley is a very low phase noise machine and it comes down to the noise of the crystal oscillator times the harmonic number in use.

I once proposed an optical wadley with a laser comb source and a tuneable laser... to make a spectrum analyser converter towards the terahertz region.


David

[Techman]

I was given the earlier model with exactly the same fault as the one being discussed here, by someone on CB radio. It seemed that it had been either the victim of a nearby lightening strike or had a transmitter 'up-it'. I noted that there was a fried resistor in the antenna input circuit, although this wasn't causing the fault. I never got round to looking at it properly and when someone asked me if they could have it, I happily gave it away, particularly as they had offered me some other piece of radio related junk that I actually had more use for in exchange. I'd removed all the case screws and put them somewhere safe, so it went without its screws. However, I eventually found the screws in a little pot about a year later - original case screws are always useful as they often go missing and I can report that they've now all been used up in other radios that have had missing screws, so not too bad in the end...don't know what ever happened to the Yaesu receiver.

[Jon_G4MDC]

Could this be it?


Or maybe not, just checked OP is in Australia.

[Phantomrose1999]

I am in Melbourne Australia. Unfortunately no time to do much. The output from the RF board to the IF/AF board is only 40mV when picking up a BC station. Seems very low.

Only have the schematic and it shows the TP0x test points.

If there a service manual ? Would be great.

[g4aaw pete]

Originally Posted by Phantomrose1999

If there a service manual ? Would be great.

All you need is here David.

http://foxtango.org/frg7/foxtangofrg7.htm

[Jon_G4MDC]

The trouble with this thread is it's reminding me that I once thought I should buy one?
They still command a decent price don't they. Still want one...just to play with.

[Radio Wrangler]

All reasonable HF receivers seem to command decent prices. There must be demand for them.

David

[Terry_VK5TM]

Have you checked the attenuator switch on the aerial input (S1 I think)?

[Julesomega]

Originally Posted by Radio Wrangler

All reasonable HF receivers seem to command decent prices. There must be demand for them.

That must be mostly a nostalgia thing, oh those happy days when the bands were full - HF during the day, LF at night - Broadcast stations, Hams, utility stations, number stations, marine and aironautical traffic.

The other use now is a poor man's selective level meter, for which the main requirement is low spurious responses. Yaesu never published anything about image frequency response for this indirect conversion set but it must be pretty good. The only 'images' which might get through will be images of the 2nd conversion, and they will be determined by the 1st IF filter which is generously spec'd

[Phantomrose1999]

Hi

I put a 3mz AM signal at the antenna and I could hear it very faintly, preselected seemed to work, main oscillator seems to work, 1mhz oscillators seems to work, but my scope shows only 10mV at the output of the RF board AND it does not change amplitude as I tune it.

Check the video out

https://youtu.be/j3I05tsQgs4

[Tyso_Bl]

Phantomrose199,

Can you disconnect the power feed to the first RF board, then feed the signal generator into the input of the tunable IF section? use a 2.5Mhz signal so it will be in the middle of the tuning range.

|You have to isolate the fault to one of the sections first.

T

[Phantomrose1999]

Did another test before bed.

https://youtu.be/rzqkE3nVob8

[Phantomrose1999]

I measured the BC antenn socket to ground. 0.6 ohms. When the ATT is in the middle position.

87.9 ohms when in the DX position

9.6 ohms when in the local position.

Almost a short between ground and the alBC antenna signal terminal. Don’t think this is normal and may explain what is happening.