10M FM - any activity these days? - Page 3 - UK Vintage Radio Repair and Restoration Discussion Forum

G6Tanuki · 27th Nov 2018, 11:27 am

Quote:

Originally Posted by GSBX1220

Some photos of my DNT 10m conversion. No add on boards or any obvious mods on this one. Not sure how it was done. I bought it for a couple of quid many years ago at a rally.

The DNT (and the similarly-synthesized Icom 1050) could be converted by linking a few pins on the PCB and adding a pull-up resistor. From memory it only thehn had 30 channels - unless you added a SPCO switch whereupon you then got 60 channels.

GSBX1220 · 27th Nov 2018, 1:36 pm

After I posted that, i done a quick google. The DNT uses a motorola PLL and changing the PLL crystal & quick re alignment you are good to go. Mine has 40 channels. No switch.

Quite a good wee set on 10

SiriusHardware · 27th Nov 2018, 2:23 pm

I take it there must be at least one more crystal in addition to the 10.240Mhz reference crystal, i.e, the 'loop mixer' crystal. A refinement would be to insert an eprom between the channel switch and PLL, programmed such that either:

(Repeater shift = off)
-All channel switch codes are passed through unaltered

or

(Repeater shift = on)
-Channel codes 31-40 are shifted down by 100Khz / 10 channels in TX
-Channel codes 21-30 are shifted up by 100Khz / 10 channels in TX.

(This assumes that channel 21=29.500Mhz and channel 40 = 29.690MHz).

Unfortunately there is only one operational 'classic' 10FM repeater in the UK that I know of, near Northampton. Another looks to be coming online soon near Norwich. Both are likely to prefer CTCSS for access.

Steve G4WCS · 27th Nov 2018, 3:16 pm

with thanks to Dave757. DNT manual and conversion details attached

SiriusHardware · 27th Nov 2018, 4:33 pm

A lovely bit of info, thanks to Dave for making it available and Steve for posting it here.

Graham G3ZVT · 27th Nov 2018, 7:36 pm

I haven't managed to track down the Bury Radio Society article, but I can tell you there were two articles in their "Feedback" newsletters
March 1983 & May 1984
Information came from this New York state club's recent publication Pages 9-13

http://home.computer.net/~pcara/docs/pcud1118.pdf

Jon_G4MDC · 27th Nov 2018, 8:14 pm

Si5351a RX VFO was patched into my 10m FM10D on Sunday.
Colpitts oscillator robbed of feedback to use as buffer.

Some issue with drive levels, not nearly as much Ic as when working as normal crystal oscillator. Si5351a is nominal 50 Ohms out with variable current drive levels set by software bits.

Making FM10 Cambridge Oscillator more like Common Emitter Amplifier and by stepping up the drive by 4:1 transformer then the buffer (as it was oscillator VT3)
Ic hit near normal levels.

It can hear things in the right places but there is a birdie at around 29.7MHz. It tunes a signal which is not there. Don't know the source of that as yet.

G6Tanuki · 27th Nov 2018, 8:22 pm

I vaguely remember that some Pye gear had the option of specifying an alternative second-conversion oscillator frequency when a harmonic would have fallen on - or close to - an intended working-frequency.

Jon_G4MDC · 27th Nov 2018, 8:34 pm

Yes it did - good recall.
This one is strange altogether. 6MHz first IF. Not recalling original build frequency no idea whether it will be 6.455MHz or else 5.545MHz as 2nd LO.
It is hidden under a cover plate - so far not removed. I calculated for them both but so far I can't find the hits to blame.

Steve G4WCS · 28th Nov 2018, 8:21 am

Quote:

Originally Posted by rambo1152

I haven't managed to track down the Bury Radio Society article, but I can tell you there were two articles in their "Feedback" newsletters
March 1983 & May 1984
Information came from this New York state club's recent publication Pages 9-13

http://home.computer.net/~pcara/docs/pcud1118.pdf

awesome, yes it was that special edition feedback article I had

Steve G4WCS · 28th Nov 2018, 12:37 pm

spent an enjoyable morning at work browsing short wave magazine

https://www.americanradiohistory.com/Short_Wave_UK.htm

found the following pertinent articles

Feb 83 simple conversion method

April 83 repeater shift

Jun 83 Further mods ICB1050

Mar 84 how to convert "unconvertible" rigs

Nov 84 ICB1050 conversion update, LCL-2740 display mod

Dec 84 ICB1050 channel scanner

Jon_G4MDC · 28th Nov 2018, 6:32 pm

I like your work!
I must be doing it wrong somewhere

Steve G4WCS · 29th Nov 2018, 11:32 am

Not really. work for a large company between contracts and havent had much to do in spells this year.
Its hard work getting up at this time of year to sit and try and look busy, when I could be gainfully employed at home doing real stuff. now if I could bring radios and a soldering iron in...

Steve G4WCS · 9th Dec 2018, 11:21 pm

Sorry if I outbid anyone on here but had to have it 😁

SiriusHardware · 9th Dec 2018, 11:35 pm

Looks in beautiful condition, so much so that I would be reluctant to modify it at all. Is that what you intend to do with it?

Jon_G4MDC · 10th Dec 2018, 10:26 pm

Time machine!
That has to be a shelf queen surely?
(Borrowed that from the pressure lamp guys - if it looks really nice but it might just blow up in actual use then that is it's destiny)

Except of course you have to know whether or not it works...

G0HZU_JMR · 11th Dec 2018, 12:45 am

Somewhere in the loft I've got a mint condition Uniden 2830 multimode CB/10m radio and this covers 10FM. I bought it when CB had died and prices were still low and couldn't resist buying it. The accessories were still sealed in plastic and unused and the radio looks new, and I mean squeaky, shiny new with no marks anywhere. It's an early model with a low serial number and still had the dealer's original anti tamper seals on it and so it hasn't been converted to cover the CB bands. I'm not sure what it's worth nowadays.

Being the early model it has a wide ceramic 10.7MHz IF filter followed by an MC3357 FM/IF chip and it is probably the worst 'CB' I've ever used in terms of signal handling. I recall that I measured the input IP3 to be about -55dBm on FM. I guess this wouldn't matter much on 10FM these days unless there was strong sporadic E propagation. It's a very pretty radio but it is technically very poor in many ways. I don't think Uniden knew how to design multimode radios properly but then again I don't think Cybernet did either.

The Icom 1050 CB was another radio that suffered badly with overload. Probably not quite as bad as the early Uniden 2830 model but I'd recommend putting a decent 10.7MHz crystal filter in it ahead of the 3357 chip.

Jon_G4MDC · 11th Dec 2018, 9:16 pm

I forget what I did to my dear old Icom 1050. £23 from the Tottenham Court Road a few weeks after 27/81 day. I drove there to buy it cash. I even managed to find a parking space. Today it would attract a 50% surcharge just for doing that.

It still hangs under my bench shelf but it has not had much use for many a year.
Squelch and S meter circuit was rubbish but easily sorted.
Later the 1st JFET mixer was replaced by dual gate.

It has some better 10.7MHz filter but for the life of me i don't know what.
Good chance ex some Pye -PMR kit. Why do I recall 10.695 MHz and thinking what a bodge.

10.240 MHz needed for the synthesiser ref but the 2nd IF conversion need 10.245MHz - so we just fudge it.
Bah ...only £23 - what do you expect?

G0HZU_JMR · 11th Dec 2018, 11:12 pm

Yes, it's definitely worth changing the filtering in some of these radios, especially if the MC3357 FM chip is being used. The two options I had for 10FM when I was first licensed was a converted Cobra 148GTL-DX CB and a Trio TS430S HF radio. I bought the TS430S new and ordered the FM module for it. The performance of the FM module was quite poor so I ended up adding my own mixer to replace the one in the MC3357 chip and I also did something to improve the (all or nothing) s meter response. I also changed the 455kHz filter to one with a narrower bandwidth. I did this within about a week of buying the radio as it was no good as a serious FM radio without these changes.

Looking back in my logbook I can see I had a local contact on 10FM about 30 years ago and it was a UK special events station in Essex that was running on 10FM. i.e. they had a GB0 callsign. I can remember hearing repeaters on 10FM back then when conditions were good.

During Christmas and New Year there is often a brief bit of sporadic E activity so it is definitely worth having a listen on 10m SSB or FM now and again around the end of December.

sidspop · 13th Dec 2018, 1:36 am

What an interesting thread his has been.
In particular the 5 pages in Ham Radio magazine to tell people how to convert a Cobra, which could be done with half a dozen diodes.
We move on to SWM from yesteryear. Names such as Harvey Lexton, Brenda and Bernie, SMC, Lowes.......all gone.
I had a 1050 years ago, modded it with the links thing. Not bothered about repeater shift then. Funnily enough I picked one up in a deal a few weeks back, complete with Dymotape label on the front saying 10FM.
I also have an interesting Cobra 148, which I managed to get legalised in the CB amnesty, about 1984 ish?
It covers 26.000 to 30.000.
BCD thumbwheels, which then feed to 4 bit adders.
4 logic levels from bandswitch, adding 100 each time.
The outputs of both of these then feed to original 4 bit adders and then PLL.
I have been doing that radio for 30 years plus, and it has never had the covers on.

27th Nov 2018, 1:36 pm	#42
GSBX1220 Pentode Join Date: Jun 2018 Location: Glasgow, Scotland,UK. Posts: 127	Re: 10M FM - any activity these days? After I posted that, i done a quick google. The DNT uses a motorola PLL and changing the PLL crystal & quick re alignment you are good to go. Mine has 40 channels. No switch. Quite a good wee set on 10 __________________ Richard

27th Nov 2018, 2:23 pm	#43
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,554	Re: 10M FM - any activity these days? I take it there must be at least one more crystal in addition to the 10.240Mhz reference crystal, i.e, the 'loop mixer' crystal. A refinement would be to insert an eprom between the channel switch and PLL, programmed such that either: (Repeater shift = off) -All channel switch codes are passed through unaltered or (Repeater shift = on) -Channel codes 31-40 are shifted down by 100Khz / 10 channels in TX -Channel codes 21-30 are shifted up by 100Khz / 10 channels in TX. (This assumes that channel 21=29.500Mhz and channel 40 = 29.690MHz). Unfortunately there is only one operational 'classic' 10FM repeater in the UK that I know of, near Northampton. Another looks to be coming online soon near Norwich. Both are likely to prefer CTCSS for access.

27th Nov 2018, 4:33 pm	#45
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,554	Re: 10M FM - any activity these days? A lovely bit of info, thanks to Dave for making it available and Steve for posting it here.

27th Nov 2018, 7:36 pm	#46
Graham G3ZVT Dekatron Join Date: May 2010 Location: Greater Manchester, UK. Posts: 18,711	Re: 10M FM - any activity these days? I haven't managed to track down the Bury Radio Society article, but I can tell you there were two articles in their "Feedback" newsletters March 1983 & May 1984 Information came from this New York state club's recent publication Pages 9-13 http://home.computer.net/~pcara/docs/pcud1118.pdf __________________ -- Graham. G3ZVT

27th Nov 2018, 8:14 pm	#47
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: 10M FM - any activity these days? Si5351a RX VFO was patched into my 10m FM10D on Sunday. Colpitts oscillator robbed of feedback to use as buffer. Some issue with drive levels, not nearly as much Ic as when working as normal crystal oscillator. Si5351a is nominal 50 Ohms out with variable current drive levels set by software bits. Making FM10 Cambridge Oscillator more like Common Emitter Amplifier and by stepping up the drive by 4:1 transformer then the buffer (as it was oscillator VT3) Ic hit near normal levels. It can hear things in the right places but there is a birdie at around 29.7MHz. It tunes a signal which is not there. Don't know the source of that as yet. Last edited by Jon_G4MDC; 27th Nov 2018 at 8:41 pm.

27th Nov 2018, 8:22 pm	#48
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,996	Re: 10M FM - any activity these days? I vaguely remember that some Pye gear had the option of specifying an alternative second-conversion oscillator frequency when a harmonic would have fallen on - or close to - an intended working-frequency.

27th Nov 2018, 8:34 pm	#49
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: 10M FM - any activity these days? Yes it did - good recall. This one is strange altogether. 6MHz first IF. Not recalling original build frequency no idea whether it will be 6.455MHz or else 5.545MHz as 2nd LO. It is hidden under a cover plate - so far not removed. I calculated for them both but so far I can't find the hits to blame. Last edited by Jon_G4MDC; 27th Nov 2018 at 8:43 pm.

28th Nov 2018, 12:37 pm	#51
Steve G4WCS Heptode Join Date: Sep 2004 Location: Preston, Lancashire, UK. Posts: 632	Re: 10M FM - any activity these days? spent an enjoyable morning at work browsing short wave magazine https://www.americanradiohistory.com/Short_Wave_UK.htm found the following pertinent articles Feb 83 simple conversion method April 83 repeater shift Jun 83 Further mods ICB1050 Mar 84 how to convert "unconvertible" rigs Nov 84 ICB1050 conversion update, LCL-2740 display mod Dec 84 ICB1050 channel scanner

28th Nov 2018, 6:32 pm	#52
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: 10M FM - any activity these days? I like your work! I must be doing it wrong somewhere

29th Nov 2018, 11:32 am	#53
Steve G4WCS Heptode Join Date: Sep 2004 Location: Preston, Lancashire, UK. Posts: 632	Re: 10M FM - any activity these days? Not really. work for a large company between contracts and havent had much to do in spells this year. Its hard work getting up at this time of year to sit and try and look busy, when I could be gainfully employed at home doing real stuff. now if I could bring radios and a soldering iron in...

9th Dec 2018, 11:21 pm	#54
Steve G4WCS Heptode Join Date: Sep 2004 Location: Preston, Lancashire, UK. Posts: 632	Re: 10M FM - any activity these days? Sorry if I outbid anyone on here but had to have it 😁 Attached Thumbnails

9th Dec 2018, 11:35 pm	#55
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,554	Re: 10M FM - any activity these days? Looks in beautiful condition, so much so that I would be reluctant to modify it at all. Is that what you intend to do with it?

10th Dec 2018, 10:26 pm	#56
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: 10M FM - any activity these days? Time machine! That has to be a shelf queen surely? (Borrowed that from the pressure lamp guys - if it looks really nice but it might just blow up in actual use then that is it's destiny) Except of course you have to know whether or not it works...

11th Dec 2018, 12:45 am	#57
G0HZU_JMR Dekatron Join Date: Sep 2010 Location: Cheltenham, Gloucestershire, UK. Posts: 3,077	Re: 10M FM - any activity these days? Somewhere in the loft I've got a mint condition Uniden 2830 multimode CB/10m radio and this covers 10FM. I bought it when CB had died and prices were still low and couldn't resist buying it. The accessories were still sealed in plastic and unused and the radio looks new, and I mean squeaky, shiny new with no marks anywhere. It's an early model with a low serial number and still had the dealer's original anti tamper seals on it and so it hasn't been converted to cover the CB bands. I'm not sure what it's worth nowadays. Being the early model it has a wide ceramic 10.7MHz IF filter followed by an MC3357 FM/IF chip and it is probably the worst 'CB' I've ever used in terms of signal handling. I recall that I measured the input IP3 to be about -55dBm on FM. I guess this wouldn't matter much on 10FM these days unless there was strong sporadic E propagation. It's a very pretty radio but it is technically very poor in many ways. I don't think Uniden knew how to design multimode radios properly but then again I don't think Cybernet did either. The Icom 1050 CB was another radio that suffered badly with overload. Probably not quite as bad as the early Uniden 2830 model but I'd recommend putting a decent 10.7MHz crystal filter in it ahead of the 3357 chip. __________________ Regards, Jeremy G0HZU

11th Dec 2018, 9:16 pm	#58
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: 10M FM - any activity these days? I forget what I did to my dear old Icom 1050. £23 from the Tottenham Court Road a few weeks after 27/81 day. I drove there to buy it cash. I even managed to find a parking space. Today it would attract a 50% surcharge just for doing that. It still hangs under my bench shelf but it has not had much use for many a year. Squelch and S meter circuit was rubbish but easily sorted. Later the 1st JFET mixer was replaced by dual gate. It has some better 10.7MHz filter but for the life of me i don't know what. Good chance ex some Pye -PMR kit. Why do I recall 10.695 MHz and thinking what a bodge. 10.240 MHz needed for the synthesiser ref but the 2nd IF conversion need 10.245MHz - so we just fudge it. Bah ...only £23 - what do you expect?

11th Dec 2018, 11:12 pm	#59
G0HZU_JMR Dekatron Join Date: Sep 2010 Location: Cheltenham, Gloucestershire, UK. Posts: 3,077	Re: 10M FM - any activity these days? Yes, it's definitely worth changing the filtering in some of these radios, especially if the MC3357 FM chip is being used. The two options I had for 10FM when I was first licensed was a converted Cobra 148GTL-DX CB and a Trio TS430S HF radio. I bought the TS430S new and ordered the FM module for it. The performance of the FM module was quite poor so I ended up adding my own mixer to replace the one in the MC3357 chip and I also did something to improve the (all or nothing) s meter response. I also changed the 455kHz filter to one with a narrower bandwidth. I did this within about a week of buying the radio as it was no good as a serious FM radio without these changes. Looking back in my logbook I can see I had a local contact on 10FM about 30 years ago and it was a UK special events station in Essex that was running on 10FM. i.e. they had a GB0 callsign. I can remember hearing repeaters on 10FM back then when conditions were good. During Christmas and New Year there is often a brief bit of sporadic E activity so it is definitely worth having a listen on 10m SSB or FM now and again around the end of December. __________________ Regards, Jeremy G0HZU

13th Dec 2018, 1:36 am	#60
sidspop Triode Join Date: Jun 2015 Location: West Bromwich, West Midlands, UK. Posts: 42	Re: 10M FM - any activity these days? What an interesting thread his has been. In particular the 5 pages in Ham Radio magazine to tell people how to convert a Cobra, which could be done with half a dozen diodes. We move on to SWM from yesteryear. Names such as Harvey Lexton, Brenda and Bernie, SMC, Lowes.......all gone. I had a 1050 years ago, modded it with the links thing. Not bothered about repeater shift then. Funnily enough I picked one up in a deal a few weeks back, complete with Dymotape label on the front saying 10FM. I also have an interesting Cobra 148, which I managed to get legalised in the CB amnesty, about 1984 ish? It covers 26.000 to 30.000. BCD thumbwheels, which then feed to 4 bit adders. 4 logic levels from bandswitch, adding 100 each time. The outputs of both of these then feed to original 4 bit adders and then PLL. I have been doing that radio for 30 years plus, and it has never had the covers on.