FRG-7. Very quiet
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As this is my favourite site, hope there are some FRG-7 experts here
Bringing one back to life but time to reach out It has low RF sensitivity, can’t peak the front end could, the S meter doesn’t move. On AM it’s very very quiet. On LSB I can hear some noise. Was able to pickup an AM station one day with a very long wire. Have replaced the 3x 3SK40 fets with originals. All voltages ok. The two oscillators are working. But there is virtually no signal at TP104. At under 1mhz I get a 180mv signal at 52mhz (I do hear noise at the speaker) but at any other frequency there is no output at TP104 Does the mixer IC fail ? SN76514 ? Any other suggestions ? David |
Re: FRG-7. Very quiet
Just at the moment all the HF bands are amazingly quiet. THere has been a geomagnetic storm, so don't judge things just now.
David |
Re: FRG-7. Very quiet
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It’s embarrassing but I can now pick up an AM station on broadcast band. But it’s so quiet off station. Zero noise. And the peaking knob is so sensitive a few mm and I will lost the station.
To actually find another station is ridiculous! The peaking knob and 1mhz tuning know must be moved in synchronisation. The S meter barely moves on AM local stations and that’s with a 6 ft wire. This can’t be normal. See photos of both oscillators working. Does this unit need a long outdoor antenna to work ? I even used a RF generator a few feet away and it can pick it up. But it’s just so insensitive. Driving me batty ! |
Re: FRG-7. Very quiet
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David |
Re: FRG-7. Very quiet
I can pick up 40m SSB as clear as AM stations with my old Marc dual on my kitchen table with the telescopic aerials
https://youtu.be/Ghj0oZWW32U Was thinking a triple conversion Unit should be better or st least as sensitive. |
Re: FRG-7. Very quiet
The Drake SSR1, which is very similar, circuit-wise, is normally fitted with a telescopic whip.
Using this, or a fairly short length of wire on the ordinary aerial terminals, it is quite lively. I remember going to the radio store, clutching my hard-earned cash in hand, to buy a FRG-7, but they were out of stock, & I got pointed at the Drake instead, otherwise I could have been more helpful. |
Re: FRG-7. Very quiet
After submitting the previous post, a bit of information came back to me.
It may not be useful, but here it is, for what it's worth. The normal method of operation with "Wadley loop" radios like this one, is to:- (1) Set the MHz control to the required band. (2) Adjust the peaking knob for maximum noise. (3) Tune across the band with the kHz knob. It is, thus, a bit more "structured" than a conventional superhet, where the bands are changed with switches, so each range change presents you with virtually a separate radio for that band. With such radios the "peaking"control just tweaks the aerial input tuning. With the SSR-1 & the FRG-7, the MHz control tunes to each of the harmonics of 1MHz, "which one", depending on the required band. The SSR1 MHz control was always a "bit off" the markings. You would move it to the "MHz" marking, then a little bit off, & up would come the noise. The Drake used, from memory, a 10 MHz crystal, which was then divided down to 1MHz, a popular modification being to change the oscillator to 1MHz directly. I think this was because Drake, or the Japanese OEM were miserly, & 10 MHz crystals were cheaper. I dunno if Yaesu did the same. |
Re: FRG-7. Very quiet
10Mhz crystals are cheaper but you can usually get them at better stability.
The bandchange switch and what you've called the peaking control are the range and tuning controls for a basic preselector. The preselector is needed to protect a fairly soft mixer from strong signals away from your wanted frequency.... Even the Racals relied a lot on their preselector. You do indeed set the MHz dial appropriately then tune the kHz dial, but, go back to the MHz dial and twiddle slightly to peak your wanted signal. This dial being off a bit is usually NOT the crystal, but a tuning error in the Wadley system filters. There are two of them and famously a nightmare to adjust. on't touch them unless you really really need to. to adjust them you need a sweeper (wobbulator) and some experience in adjusting higher order filters. David |
Re: FRG-7. Very quiet
I've just had a quick look at the circuit diagram,
http://www.monitor.co.uk/radio-mods/...it-diagram.pdf I see that there is an awful lot of switchery in front of the receiver. I am assuming that the DX/Off/Atten switch has been set to 'DX' throughout? One thing you could try is to connect a long length of wire directly to C101, not the side which goes to Q101 G1, but the side which goes to the junction of VC1 / S2c common. Connecting an aerial here bypasses the input bandpass filters, but if the receiver livens up when you do that, that would suggest a fault between the aerial input and the beginning of the receiver proper. |
Re: FRG-7. Very quiet
That snippet shows a 1MHz crystal, X301, as the basis for the harmonic generator.
Any old MW radio should be able to hear that running when held in proximity. No 1MHz and there will be nothing else. It could be a sleepy crystal. Maybe the weak AM station was just breakthrough at tunable IF? |
Re: FRG-7. Very quiet
does it have a fuse ie a lamp fuse on the input? ei7ka
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Re: FRG-7. Very quiet
As per FT747 / FT757? Not according to the diagram (post #9).
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Re: FRG-7. Very quiet
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It’s the AM BC that has zero background noise until I find a station. But the preselected and kHz tuner are incredible sensitive and this difficult to align both to get a station on BC. |
Re: FRG-7. Very quiet
I think the bottom band, for doing AM broadcast medium wave reception may have an inbuilt attenuator, in the assumption there will be bigger signals. I seem to recall FRG7s were quieter. A number of other sets played this same trick.
David |
Re: FRG-7. Very quiet
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I think you are right David. The Local DX Switch Attenuator path is different between range A and the other three ranges.
The other thing this has is an LED indicator that shows when you are tuned on a 1MHz band segment. It seems it is lit when off tune and it goes out when MHz dial is correctly tuned. I wonder whether that behaviour can be observed on this set? It works by detecting the level of 1st LO mixed with the 1MHz harmonic as observed at the end of the narrow (52.5MHz) filter. Do these paths through the Local/DX switch meet general agreement? |
Re: FRG-7. Very quiet
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There is almost no measurable output at pin 3 of the mixer IC. The output from the RF board to the IF/amp board is 40mv during a broadcast station. Thought it should be higher ? If I put my finger on the same connection I get static from the speaker so the issue is in the RF board. Will post waveforms at the key test points |
Re: FRG-7. Very quiet
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Re: FRG-7. Very quiet
You won't see much at Q106 Pin3. It takes 3 stages of gain before they can do anything useful with it.
What about the Lock LED behaviour? If you want to look for mixer output look after the gain at TP110 - this is where the detector for the LED is so we know there should be some go there - if all is well... |
Re: FRG-7. Very quiet
Some thoughts, does the OP have the instruction/service manual, the Yaesu one? It has all the test voltages and alignment info in there, and the instructions on how to drive the radio, it really isn't like anything else. The input attenuation switch oddly is at its most sensitive on the middle "normal" setting, the DX setting drops the signal, and the local setting even more. Which aerial input is being used? Linking SW1 & BC then feeding the aerial into the coax socket should give the best sensetivity on the BC band.
If the voltages look good when checked against the service manual, check the 2nd tunable IF, it tunes 3 to 2 MHz, backwards, with the L.O 455kHz higher than the input signal, if that works OK, then turn attention to the 1st IF / RF board. Can the OP report back if the tunable IF section is functional first. Is there any known history to the set that may help an online diagnosis? T |
Re: FRG-7. Very quiet
The well documented modification replacing the "lock" LED with a dual-colour one is
simple and worth doing. I have noticed that near the ends of some preselector bands it is worth selecting the next band up or down and tuning for mximum signal, there is some overlap. |
Re: FRG-7. Very quiet
I can very well understand the point about preselector overlap.
What does a dual colour lock LED achieve plz? |
Re: FRG-7. Very quiet
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. |
Re: FRG-7. Very quiet
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 |
Re: FRG-7. Very quiet
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! |
Re: FRG-7. Very quiet
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 |
Re: FRG-7. Very quiet
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. |
Re: FRG-7. Very quiet
My guess is there's 2 random noises of the same spectrum added together so will give 6dB worse (phase)noise
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Re: FRG-7. Very quiet
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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 |
Re: FRG-7. Very quiet
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.
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Re: FRG-7. Very quiet
Could this be it?
:laugh2: Or maybe not, just checked OP is in Australia. |
Re: FRG-7. Very quiet
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. |
Re: FRG-7. Very quiet
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http://foxtango.org/frg7/foxtangofrg7.htm |
Re: FRG-7. Very quiet
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. |
Re: FRG-7. Very quiet
All reasonable HF receivers seem to command decent prices. There must be demand for them.
David |
Re: FRG-7. Very quiet
Have you checked the attenuator switch on the aerial input (S1 I think)?
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Re: FRG-7. Very quiet
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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 |
Re: FRG-7. Very quiet
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 |
Re: FRG-7. Very quiet
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 |
Re: FRG-7. Very quiet
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Re: FRG-7. Very quiet
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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. |
Re: FRG-7. Very quiet
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T |
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What should I see at TP107 ? Does the first mixer IC fail ? I found no measurable output at pin 3 with my digital Cro. |
Re: FRG-7. Very quiet
Quick update.
I am chasing the 52mhz signal that is mixed at Q105. I am getting a signal at Q109. Can see a signal that peaks every 1mhz while tuning the main vfo. Can’t see anything beyond Q109, the led drivers are not getting signal to turn around t on/off Will remove Q109 and test it. Seems to get a signal at the base that peaks every 1mhz but nothing at the collector. |
Re: FRG-7. Very quiet
You are getting close...
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Re: FRG-7. Very quiet
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Great news ! Fixed.
https://youtu.be/s_CukzwFccI As mentioned there was almost no output at TP104. Even after replacing the Q101 and Q104. It was able to pick up strong signals including some BC stations. That is what threw me. Next I checked all oscillators and they were working So I checked the signal from pin 3 of Q106 through Q107, Q108, Q109. Then I found no signal beyond Q109 ! Removed Q109 and found it to be dead. Removed Q108 and it had an hfe of 90. I had two 2SC930’s which had a hfe of 110 and 130. So I put them in as they are pin compatible and was so excited that it was picking up shortwave with just a wire. So all good. Will recap the unit someday. |
Re: FRG-7. Very quiet
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Had to delete the video because something is confusing.
Why am I getting a 53 MHz signal at TP104 ? The schematic says it should be 2-3mhz. ??? |
Re: FRG-7. Very quiet
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This is my output at TP104. Anyone care to explain what I am seeing ? It’s the same signal regardless if a station is tunned or not. Nothing anywhere near the 2-3mhz the schematic indicates.
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Re: FRG-7. Very quiet
TP104 is connected to the drain of the mixer, Q105 via a 22pF capacitor. Q105 is a simple mixer, the output of which will be composed of the signals made up from the input into the gate, the input into the source, the sum of these, the difference frequency plus the many harmonics and their sums and products.
The source load of Q105 only a choke, not a tuned circuit, so you will see the whole lot of frequencies when you look at TP104, although some may be attenuated a little by the tuned circuit formed by T401, VC2 and TC401 which is fairly loosely coupled to the output of the mixer. The difference frequency of 2-3MHz is selected by the tuned circuits later on (T401, VC2 and TC401 then T402, VC2 and TC402) I expect the dominant signal to be the one from the oscillator side chain, which presumably is 53MHz. The good news for you is that all is as it should be. Paula |
Re: FRG-7. Very quiet
Thanks Paula. Makes sense.
I have reposted the video. https://youtu.be/rzqkE3nVob8 Working very well. Am really pleased with it. Will hook it up to my 6m copper loop and try for 40m hams tomorrow. |
Re: FRG-7. Very quiet
A good conclusion. Enjoy it now.
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