UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Amateur and Military Radio

Notices

Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

Closed Thread
 
Thread Tools
Old 16th Mar 2021, 1:35 pm   #1
Wendymott
Octode
 
Wendymott's Avatar
 
Join Date: Jun 2013
Location: Huddersfield, West Yorkshire, UK.
Posts: 1,639
Default Yaesu FRG7

Hi Peeps. In other postings "not this section" I have been muttering about the FRG7. However ..this is specific to this model and I cannot understand what is going on. I have the manual, so I can refer to it. I was asked to look at X 4 receivers, and to select one for myself. Fortunately, after finding the stupidly located internal switch that reduces the audio output level, I was able to get them all in a reasonable working condition. However being fair.. I decided to keep the one with a problem that I " would come back to later".
I am fortunate to have a decent Spectrum analyser with tracking generator .. so checking the two band pass filters T105 - T108 (55 Mhz)... and T109 - T116 selective filter 52.5 Mhz, I was able to check these, but looking at the manual.. page 11, to me.. it was impossible to decide what the two markers should be set at... and how steep the slopes should be. I was able to set the shape reasonably, and the loop locked ok.
However..when using the receiver tuning control 0 - 1000...the receiver suddenly goes deaf (- 40db) down at 900 Khz - 1000.
Its ok at 800 Khz and below.
When adjusting the control, there is a loud clicking / crackle at certain points as though there is an intermittent short of the tuning cap vanes, but this has proved not to be the case.
I have fitted a two filter solution for 455 Khz, but obviously this has no bearing on the problem. (see photo)
It would be a nice receiver if I can sort out this problem.
Are there any experts of the FRG 7's out there ?
Attached Thumbnails
Click image for larger version

Name:	Filter mod 2.jpg
Views:	172
Size:	45.9 KB
ID:	229303  
__________________
Should get out more.

Regards
Wendy G8BZY

Last edited by Radio Wrangler; 16th Mar 2021 at 3:18 pm. Reason: Yeasu?
Wendymott is offline  
Old 16th Mar 2021, 3:22 pm   #2
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 20,863
Default Re: Yaesu FRG7

Does it crackle in response to a number five single-handed thump?

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline  
Old 16th Mar 2021, 9:38 pm   #3
Wendymott
Octode
 
Wendymott's Avatar
 
Join Date: Jun 2013
Location: Huddersfield, West Yorkshire, UK.
Posts: 1,639
Default Re: Yaesu FRG7

Ermmmmmmm... how did you guess Although a number 4 was adequate
"E" before "A" or "A before "E"...... grammar was never my best subject..cest la vie
__________________
Should get out more.

Regards
Wendy G8BZY
Wendymott is offline  
Old 16th Mar 2021, 10:08 pm   #4
Julesomega
Octode
 
Julesomega's Avatar
 
Join Date: Dec 2012
Location: Stockport, Greater Manchester, UK.
Posts: 1,686
Default Re: Yaesu FRG7

Wendy, I'm sure you have set your markers as shown on p11 and peaked both BPFs as shown, which will get the performance back to factory specs, but knowing you I expect you will want to add more elements to both. The harmonic filter would benefit from slightly better rejection at 1MHz to keep 15MHz blowtorches out of 20 metres etc. I will be interested to see what you come up with!
__________________
- Julian

It's good here
Julesomega is offline  
Old 16th Mar 2021, 11:29 pm   #5
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 20,863
Default Re: Yaesu FRG7

Could be the sliding earth contacts for the tuning capacitors (either MHz or kHz) making an iffy contact.

Everyone forgets they're there.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline  
Old 17th Mar 2021, 1:58 pm   #6
Wendymott
Octode
 
Wendymott's Avatar
 
Join Date: Jun 2013
Location: Huddersfield, West Yorkshire, UK.
Posts: 1,639
Default Re: Yaesu FRG7

Hi David......I did give the contacts some cleaning lube.... but I will give it another go..

Julian. I will give it a go and report back. I am in the middle of trying to solve another problem. There have been several suggestions and ideas to reduce the 455 Khz I. F passband, which included using a CFR455 J filter and various switching ideas...One of the 4 receivers had this module fitted which had ugly long miniature coax wires to various points...I removed all this "gubbins" and placed the original filter back into its rightful place. I then made a small pcb with two filters and a small DPDT relay, and "piggy backed" the module directly over the original position.
Mechanically it works a dream... however.. for some reason there is an 18 db insertion loss..... proved by removing the module and re fitting the filter.
Was it the relay ? I re made the pcb with a micrometals DPDT relay......refitted..... it is NO better. At this moment.. I have refitted the original filter, just to check.... When I have it sorted I will report back.
__________________
Should get out more.

Regards
Wendy G8BZY
Wendymott is offline  
Old 17th Mar 2021, 2:23 pm   #7
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 20,863
Default Re: Yaesu FRG7

Some of the narrower ceramic filters have a fair bit more insertion loss, but have a look at the terminating impedances yout filters expect. This could be the problem. It also screws up the passband ripples.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline  
Old 17th Mar 2021, 4:48 pm   #8
Wendymott
Octode
 
Wendymott's Avatar
 
Join Date: Jun 2013
Location: Huddersfield, West Yorkshire, UK.
Posts: 1,639
Default Re: Yaesu FRG7

David... It is "like for Like" as in the original is part of the mod... I have got back one of the tested receivers to use as a comparison ... watch this space
__________________
Should get out more.

Regards
Wendy G8BZY
Wendymott is offline  
Old 18th Mar 2021, 3:42 am   #9
majoconz
Heptode
 
majoconz's Avatar
 
Join Date: Jan 2008
Location: Ashhurst, Manawatu, New Zealand
Posts: 550
Default Re: Yaesu FRG7

Wendy...my Frog came with copies of articles written by the very knowledgeable J.L.Linsley Hood - he goes into great detail of the innards and alignment of most of the tunable bits. The articles were in the "Short Wave Magazine for September and October 1981 - he goes through quite deeply the need for good alignment of the 54.5 to 55.5MHz first IF bandpass filter and then emphasizes the need for good alignment of the 52.5Mhz selective amplifier.

Aha - lookee what I found...

https://worldradiohistory.com/UK/Sho...WM-1981-09.pdf

https://worldradiohistory.com/UK/Sho...WM-1981-10.pdf

Hope your Frog now turns into a handsome Prince....
__________________
Cheers - Martin ZL2MC
majoconz is offline  
Old 18th Mar 2021, 4:31 am   #10
majoconz
Heptode
 
majoconz's Avatar
 
Join Date: Jan 2008
Location: Ashhurst, Manawatu, New Zealand
Posts: 550
Default Re: Yaesu FRG7

...and here's something else you may like...

https://worldradiohistory.com/UK/Sho...WM-1979-08.pdf

page 282 onwards
__________________
Cheers - Martin ZL2MC
majoconz is offline  
Old 18th Mar 2021, 9:13 am   #11
Wendymott
Octode
 
Wendymott's Avatar
 
Join Date: Jun 2013
Location: Huddersfield, West Yorkshire, UK.
Posts: 1,639
Default Re: Yaesu FRG7

Hello Martin. Thanks very much for the links I do have a lot of articles logged and listed..What would we do without the Worldhistory web site, and This forum. I will re visit those articles you have stated....
The Frog 7 is a "Twiddlers" delight.... and obviously not many will be fortunate to have the proper equipment.
Last night I spent most of the evening measuring and testing the other FRG 7 making a Service manual, or should I say..... appendix to what is there already.
Looking at the schematic of the FRG7 and notes from Murata, it seems that Yaesu had other ideas about matching the output of the filter, in as much the filter goes straight into the Base of Q405, no sign of matching, unless Q405 is 2K which is what Murata specifies...I am going to play with a filter and my SSA3012 to see what improvements can be made. The ripple of the filter is quite noticable at present....


I
__________________
Should get out more.

Regards
Wendy G8BZY
Wendymott is offline  
Old 18th Mar 2021, 11:48 am   #12
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 20,863
Default Re: Yaesu FRG7

Excess ripple on a filter is usually a reliable indication that it isn't being presented with the right impedances.

They are designed as a series of coupled resonators and the resistive part of the termination at each end is used to set the Q of the first and last resonators. The inner resonators have their Q's set by coupling to the loaded outer resonators. Get the loading wrong and it all goes wrong quite quickly.

Sometimes, the resonance of the outermost resonators is offset to accommodate some capacitance in the circuits the filter goes into. So seeing something like 500 Ohms//8pF isn't an admission of imperfection, it's done as a convenience for the designer of the circuitry around it.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline  
Old 18th Mar 2021, 12:40 pm   #13
Restoration73
Nonode
 
Restoration73's Avatar
 
Join Date: Jun 2013
Location: Surbiton, SW London, UK.
Posts: 2,711
Default Re: Yaesu FRG7

Whilst I do not know the specific problem I modified one for selectable 6/2.7kHz filtering
around 1985. I used CFM455J1 2.7 filter from Cirkit. It is essential to keep the
input and output screened (I used tinplate) with 2 off SPDT relays.
The performance was excellent and I did not remember much loss.
The owner was into MW and tropical band dxing and was well satisfied.
Restoration73 is offline  
Old 18th Mar 2021, 3:30 pm   #14
Wendymott
Octode
 
Wendymott's Avatar
 
Join Date: Jun 2013
Location: Huddersfield, West Yorkshire, UK.
Posts: 1,639
Default Re: Yaesu FRG7

Hi David. I read a very useful missive from Murata re Filters... and they were decidedly keen on correct matching..obviously Yaesu decided to cheapen the design with no output matching ..... however.. this does not alter the fact that with the original filter in place, and putting it approx 30mm away on the module, would account for such a loss.
However... I now know why the sensitivity is low... compared with the other receiver. The 52.5 Mhz signal at TP103. is 120m/V compared with 360 m/V on the good receiver....so 220 m/V is getting lost between Q102/103 and the output. I know the filter is tuned correctly using the SSA3012, but somewhere the signal is getting lost...hopefully I will find it before I expire
Ok Resoration73...I am using one DPDT relay, but I am not after "perfection" , but I will take on board what you say, and if it isnt acceptable.
__________________
Should get out more.

Regards
Wendy G8BZY
Wendymott is offline  
Old 18th Mar 2021, 3:41 pm   #15
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 20,863
Default Re: Yaesu FRG7

Yes, that much lower mixer drive is enough to explain your loss in signal path gain.

I think you're on the right track.

And the filter in the signal path of the Wadley should be wider than that in the LO path, and it should, ideally be flat topped. Do-able in an RA17 with a sweeper, but the frog-7 filters are a bit more, um, simplistic.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline  
Old 19th Mar 2021, 9:21 pm   #16
Wendymott
Octode
 
Wendymott's Avatar
 
Join Date: Jun 2013
Location: Huddersfield, West Yorkshire, UK.
Posts: 1,639
Default Re: Yaesu FRG7

Problem solved. After chasing my "tail" for a few hours...... not really knowing the receiver, I went back to comparisons of RX1 and RX2. With a 3 Db X 2 splitter with equal signals to both, the 455 Khz IF output of RX1 was 20 Db up on RX2. Closely looking at the filter input. RX2 had no 455 Khz component at all...... the upshot of this was Q402 2SK16 Fet O/c, it mixes the 2 - 3 Mhz RF with the VFO. Replacing Q402..back to full operation.. Refitted the 2 X I.F Filters, on a pcb module , piggy back style..
I would suggest this RX was sold, Deaf or not working, but the vendor forgot to mention it..I am really glad I had another for comparison.
End of Saga.
__________________
Should get out more.

Regards
Wendy G8BZY
Wendymott is offline  
Old 19th Mar 2021, 10:05 pm   #17
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 20,863
Default Re: Yaesu FRG7

A comparison set... yup, that makes life easier. some might even consider it cheating.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline  
Old 19th Mar 2021, 10:30 pm   #18
Wendymott
Octode
 
Wendymott's Avatar
 
Join Date: Jun 2013
Location: Huddersfield, West Yorkshire, UK.
Posts: 1,639
Default Re: Yaesu FRG7

What ever.....
__________________
Should get out more.

Regards
Wendy G8BZY
Wendymott is offline  
Old 21st Mar 2021, 3:15 pm   #19
John KC0G
Pentode
 
Join Date: Mar 2009
Location: Minneapolis, Minnesota, USA.
Posts: 236
Default Re: Yaesu FRG7

Wendy, well done. Please, what did you us as a replacement for the 2SK16?

Thanks and 73, John KC0G
John KC0G is offline  
Old 21st Mar 2021, 10:06 pm   #20
Wendymott
Octode
 
Wendymott's Avatar
 
Join Date: Jun 2013
Location: Huddersfield, West Yorkshire, UK.
Posts: 1,639
Default Re: Yaesu FRG7

Hi John... a BF 256A single gate Fet.
__________________
Should get out more.

Regards
Wendy G8BZY
Wendymott is offline  
Closed Thread

Thread Tools



All times are GMT. The time now is 4:34 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2023, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.