10M FM - any activity these days?
 

It is now 37 years or so since CB 27/81 day.
That is a long time!

Once the importers sorted out a few things there were the ICOM 1050 and such like 40ch transceivers which could be modified for 10m FM. They typically cost about £25 as I recall from the Edgware Road and similar.

After a few years 10m FM actually had some users - people modified the rigs in various ways, mixer crystal changes, pulse swallow counters etc+ etc. I forget.

How is the band today? Is anyone still on? I hear nothing except when there is DX.

I am tying to decide what to with this FM10D Cambridge which was discussed 2 years ago here. https://www.vintage-radio.net/forum/...d.php?t=129484

It works but it is on useless frequencies due to the available crystals.

I have now done enough work on a PIC+Si5351 VFO to make it 10m FM full tunable. The question - is that worth doing or should I rewrite the code by -2MHz and use it for a CB monitor?
Maybe I could auction it like that with all the TX guts ripped out ...(not a serious suggestion) :laugh1:

Re: 10M FM - any activity these days?
 

10FM still comes active sometimes when the ionosphere's in the mood to play - in the past I worked through a bunch of US repeaters in the 29.5-29.7Mhz band area (they use 100KHz split).

But in these times of minimal sunspots the entire 10M band is deathly silent, whether you're using FM, AM, SSB or CW. These days I can't even hear the Sunday or Thursday NADARS natter-nets on 28.305MHz SSB.

Re: 10M FM - any activity these days?
 

Thanks! A little bit as suspected.

Back a long time ago the US repeaters made excitement. But the QSOs did not for the most part.

Putting the -100kHz TX split in the rigs was also achieved in various ways - some were very cunning.

I was hoping to learn about local inter-G or Europe activity to be honest. I haven't heard much in a long time but I don't monitor.

Sorry I don't know what NADARS is - been working on that. At least if on 28.305 (top channel reachable by old CBs) it must be either a CB net or an Amateur net wanting to "keep" the frequency. I wonder which it is.

Re: 10M FM - any activity these days?
 

NADARS is Newbury and District Amateur Radio Society - they have a couple of weekly 28MHz SSB nets - Thursday evening and Sunday. I used to be able to work them (just) - it's 30-odd miles - but haven't heard them for ages.

Re: 10M FM - any activity these days?
 

From the late spring to late summer there is usually a good -technical- chance of hearing / working stations in continental Europe during daylight hours.

Unfortunately activity is likely to be so comparatively low that the easiest way to find out whether there's a lift on is to listen to 11m, and when you notice a lot of incoming on that band, put a few calls out on 10FM yourself.

Re: 10M FM - any activity these days?
 

Thanks for explain NADARS - also at the limit of my range too, or beyond, but not left wondering!

I have been listening to 10m since being a kid at school. Ex AM CB walky talky experience and so on. A Skyfon (number escapes me) on 27.125 (Ch14) was fun in some summer - '76 maybe?

It just seemed to me that 10m FM had some good activity after the advent of cheap 27/81 rigs. It continued for a few years and then it died.

In my locale there was a historical AM net on 28.889 - no idea why. I think somebody had a gold mine of crystals and they leaked out through the clubs.

Re: 10M FM - any activity these days?
 

I was surprised by the ingenuity employed by some people to get the largely intentionally 'immovable' UK spec radios to shift upwards by 2Mhz or so given that the PLL ICs had been expressly designed to make exactly that sort of thing impossible.

There were two main approaches weren't there, one being to mix the output of the VCO with an oscillator and then feed the resulting (VCO minus oscillator) frequency to the input of the PLL so that the actual VCO frequency was shifted up by 2 Mhz.

The one which really impressed me was the pulse-stealing method which would digitally remove one in every n pulses from the output of the VCO before feeding it back into the PLL, so that the VCO frequency seemed lower than it really was and was duly accordingly raised. That must have been a real light bulb moment on someone's part.

All of this was also complicated by the fact that the VCO frequency had to be 1/2 TX frequency on TX, as well.

There were a few very rare UK models which used unrestricted PLLs, among them the JWR M2, the nearly identical ICOM ICB 1050 and the early version (only) of the Binatone Route 66. Later versions of that used the UK-specific LC713x PLLs.

I acquired a Rotel RVC 220 which had been converted to 10FM using the 'digital' method but, finding no activity on 10FM, restored it to as-new working order on its original frequencies.

Re: 10M FM - any activity these days?
 

Yes, we are raking history here for sure. Better try to catch it before it's all gone?

As you say the Icom ICB1050 which I have was based on MC145106 synth chip and mix down crystals. Change the crystals it all just worked. Switch the TX mixing crystal for a repeater shift of -100k. I did mine that way and still have it. The expensive method. 3x crystals to buy.

Then there was the Eprom method which was in effect adding to the divider ratios to achieve the same thing. Much cheaper to do. TX shift just switched a different address bank.

The LC71xx equipped sets which I can't remember (never had one) was the technique of disappearing some pulses and it will never notice. Not having had one I have no experience but I always suspected it could result in jitter in the synthesiser. Did it? No idea.

The ICB1050 had some other evils - one Squelch and S-meter related. Also the first RX mixer was quite poor. Not to mention the 3rd harmonic of 10.24 which was used on the TX path coming out at 30.72 - try getting rid of that!

Re: 10M FM - any activity these days?
 

I worked a station around 15 miles away on 10m SSB a couple of weeks back, but that was cheating a bit as it was pre organised.

Never hear anything on 10 unless there is a lift on. Dead otherwise. Shame really as it's good for local nets.

I have a DNT CB converted for 10FM. Picked it up years ago at a rally for something like a fiver. I do remember hearing the stateside repeaters, but I was never sure if the shift was set on the rig.

Re: 10M FM - any activity these days?
 

Prompted by this thread, I went a-hunting in the deepest darkest depth of the garage and found this:
Attachment 172931
Evidence of my ham-fisted 1980s handywork
Attachment 172932 Attachment 172933
Looks like I used a couple of 4008 4-bit adders
Attachment 172934

I also have a more generic CB set with a 10M mod using a mixer, but that will have to wait until I can search the deepest darkest depths of the cupboard-over-the-downstairs-toilet.

I probably still have a set that was not modified for 10m but instead had a simple tone-squelch/selective calling mod, the XYL had a similar set at home, and I would call her up if I was able to come home for lunch.

Oh how the fowl-mouthed breakers-on-the-side hated us when we didn't reply to them, because we couldn't hear them!

Re: 10M FM - any activity these days?
 

One D-D-D-of-the-C-U-the-D-T search later, and I found this:
Attachment 172936 Attachment 172937 Attachment 172938
What a mess!

Attachment 172943
So this was the mixer method. All I remember is the cct was known locally as the Bury Radio Club circuit.

Let's see, an MC1496, normally used as a balanced modulator, a 7492 /12 counter, I know the other two things are miniature relays, what did they do? Transmit/Receive switching I suppose.

And if that's an oscillator in the middle where's the active device? I know from recent experience that the MC1496 normally has an external osc.

Must be over 30 years since I've seen this. Frightening.

Re: 10M FM - any activity these days?
 

The use of the adder ICs was common in certain export radios, where again an ingenious trick was employed to generate LOWER frequencies than the original ones, by adding such a high value to the binary value supplied by the coded switch that the 8-bit output of the adders would 'clock', producing a lower binary value than the one being passed in by the switch.

I've just had a look around for a circuit description of the 'analogue/mixer' method of upshifting but failed to find it anywhere. Spectrum communications, who for a long time did do a PCB based on that principle, no longer seem to do them. The digital pulse-stealing method is well described in one of two collected volumes of 'The Midnight Express', a kind of 'Rig Doctor' newsletter which was going around at the time.

Re: 10M FM - any activity these days?
 

I did an Icom, I think I used the 4008 adder circuit that covered 29.31-29.70.
there was also a display mod to read 31-70, and various other filter mods, replacement fet front end etc.

I still have the photocopied leaflet from the Bury Radio society that has details of all the mods.

back in the day the local radio club bought all the Icoms available locally and we used them as local natter boxes, but yes, it was easy to work into the states on 4 watts FM.

I shouldnt imagine there isnt much up there at all nowadays.

Re: 10M FM - any activity these days?
 

if you ever get time would you mind uploading a copy / scan of the leaflet, or at least the circuit to this thread? I'd be interested to see it. I'm sure others would too. I couldn't find any reference to it anywhere else online.

Re: 10M FM - any activity these days?
 

Ill try and scan it in tomorrow, but if I recall the photocopying quality isnt the best. will I be able to upload it to here as a .PDF ?

Re: 10M FM - any activity these days?
 

Yes, if it isn't too large, um.... (just a second). OK, maximum size for a PDF is 1.91MB.

If you can't get it that small without making it unreadable, try making it into a .zip file - maximum file size for .zip files is also 1.91MB but you can usually fit a bit more than 1.91MB of uncompressed 'other' file into a .zip file, if you see what I mean. I assume this is a monochrome document, so don't make the file bigger than necessary by scanning it in 256-bit colour, probably 16-bit or 8-bit greyscale would be good enough.

Re: 10M FM - any activity these days?
 

It would be good to capture that mod info. The discussion is raking up some history isn't it?!

My FM10D VFO is ready to go tuning 28.8 to 29.7 in 1kHz steps, shift of -100k for repeaters and +6.0MHz RX LO out (RX is 35MHz crystals). TX uses another output and is divided by 12 (2.5MHz crystals).

Next to do is some interfacing.

I suppose in on the base /grid of the oscillator transistor/valve but remove the capacitors which make them Colpitts. That needs doing in some very sympathetic way - why I am taking my time doing it.

Re: 10M FM - any activity these days?
 

Are you directly FMing that synth PCB, or is the FM being applied to something else which the output of that is mixed with?

I found an interesting article here

https://zissisprojects.wordpress.com...rduino-ad9850/

where someone has a go to 'FM' one of the ubiquitous AD9850 modules in real time using audio read from one of the micro's ADC inputs, in this case using an Arduino, rather than the PIC which you are obviously using (I have quite a few of those 44-pin PIC demo boards - very useful).

I was also wondering, actually, whether a modern micro like a PIC running at 40Mhz (10Mhz * 4) would be fast enough to do the pulse stealing trick by itself, because handling the TX / RX shift and any other shifts required would then be quite trivial.

Re: 10M FM - any activity these days?
 

haha, no, as written the TX output is divided by 12 so the original FM10D's phase mod at 2.5MHz can do the FM for me. That also means minimal mods to what is an almost mint condx set inside.

There is another similar chip, the Si570, which has ability for direct FM if you order the right variant. Those are expensive to buy.
I have one in something else "just for research purposes". They seem to just manage 5kHz dev at 2m and so 2.5kHz at 4m.

They might be OK at the 10m FM dev specs but struggling I suspect.

Hope you like the display - inspired by Yaesu FT207 !!

Re: 10M FM - any activity these days?
 

...and the Yaesu FT290, etc, none of which displayed more than the important part of the frequency.

I have some small PCBs which have 5 * mini 7-segment LEDs and a serially accessed MAX...something or other LED driver IC on them, perfect for that sort of project. I had intended to state the IC part number but of course I can not find them just now.

As the missing first digit would always say '2' anyway, there seems little to stop you from adding a fifth display and just hardwiring it for digit '2', although you'd have to experiment with a pot to find the right segment series resistor value to get the segment brightness the same as the four existing (presumably multiplexed) displays.