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

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Old 15th Sep 2013, 2:13 pm   #1
Biggles
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Default Dymar 1995 PMR set.

Hi all, I've just found an old "Dymar 1995" ex PMR set in the shed while looking for something else and was wondering if anyone has a circuit or better still a service manual for one so that I can convert it for two metres which was the original intention about ten years ago.It has an eprom programmed synth which will lend itself nicely to the task in hand....if I had some info!
Alan.
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Old 15th Sep 2013, 6:29 pm   #2
Restoration73
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Default Re: Dymar 1995 PMR set.

Is this the same set ? GWM sold second user Dymar.
http://www.davidmpye.co.uk/files/dym...Conversion.pdf
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Old 15th Sep 2013, 7:10 pm   #3
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Default Re: Dymar 1995 PMR set.

Thanks for the link R73. It's difficult to tell whether it's the same set without any layout diagrams or a circuit. There may well be similarities. I got the set from a radio rally and it came with an eprom for two metres. I have repaired a faulty regulator which was preventing it from powering up this afternoon so things are looking promising but it's always easier with a bit of service info. Cheers.
Alan.
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Old 25th Oct 2013, 12:23 am   #4
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Default Re: Dymar 1995 PMR set.

A load of these became available in this area from Northern Gas in the mid nineties and a lot were successfully converted to 2m from their original 'M' band coverage. The 'D' and 'E' variants were the ones which (converted) worked the best, some converted 'F' version models also came onto the market but they didn't seem to be as stable on TX as the earlier versions, possibly because the conversion for the D/E models had just been adapted for the 'F' version rather than devised specially for it.

One strange problem they often suffered from when used on FM was microphony of the VCO module, causing what sounded like acoustic feedback in receive mode. Sound from the internal speaker bouncing around inside vibrated the VCO, bouncing it off frequency and producing an audio frequency difference between the VCO and the incoming signal, which created audio output from the speaker, which vibrated the VCO even more, etc. The easiest fix was just to disconnect the internal speaker and use an external speaker.

Which version do you have there? D, E, or F? I may have the diagrams.
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Old 25th Oct 2013, 12:39 am   #5
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Default Re: Dymar 1995 PMR set.

Quote:
Originally Posted by Restoration73 View Post
Is this the same set ? GWM sold second user Dymar.
No, that's a Dymar 2000 - completely different model - coincidentally the very type of radio I made my first ever amateur radio contact on in 1994. In fact, it was the only ham radio I had for quite a while after I got my licence. I eventually gave it to a local ham who was stuck with a crystalled single-channel PMR set as his only ham radio.
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Old 26th Oct 2013, 1:19 am   #6
Biggles
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Default Re: Dymar 1995 PMR set.

Hi Sirius, I'm not sure which version I have but I will check. The set I have came with a very poor copy of the circuit so any info would be helpful. The original channel plan would match with being ex utility use as the frequencies were around 138/9 MHz. I have an eprom programmed for 2m but I am in the process of decoding the eprom data so I can change it to my own requirements. I had to change a couple of components in the VCO to get it to lock reliably on 2m. The main attraction is that it is an AM/FM set by the look of things. The project has been shelved for a month or so while I finish building a receiver I am busy with at the moment, but will continue before long so hopefully I will be able get it working properly.
Alan.
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Old 27th Oct 2013, 11:38 pm   #7
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Default Re: Dymar 1995 PMR set.

I believe they were on 'M' band which as you say was about 139Mhz RX but usually a much lower TX frequency at around 109Mhz, which meant that the transmitter had to be physically modified to work on 2m. I have a folder full of stuff related to them, but it's possible that it may all relate to the 'F' version as that was what I had (for a while). Yes, they were originally used on AM but they do have FM built in as well, quite unusual, I would have thought.

The info I have may include the method for calculating the eprom data, but again, that may relate to the 'F' version only. I remember that when I bought mine (already converted) there was at least one programming error in the provided eprom (one RX or TX frequency wrong) and I managed to understand the format enough to correct the error. That was a long time ago, though.
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Old 28th Oct 2013, 12:42 am   #8
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Default Re: Dymar 1995 PMR set.

I had a look on the type plate on the back and it says 1995-3 so I don't know which version that relates to. At the moment the Rx is working ok so I may just leave it at that. I am about two thirds of the way to breaking the code to reprogram it but as most of the channels I require on Rx are there but in the wrong order for my liking I will probably just put up with it. The synth programming protocol is in a data book I have for the NJ8820 chip, and I think the only other funnies are probably for AM/FM selection (one bit) and TX/RX frequency selection (one bit) and I can read the synth output frequencies so I'll get there eventually. Info on eprom data would still be helpful though if you have it to hand.
Alan.
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Old 28th Oct 2013, 10:31 pm   #9
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Default Re: Dymar 1995 PMR set.

You said you had 'an eprom' for 2m - now that I've had a look through the info that suggests it is an 'F' type, as the D and E versions used a pair of eproms side by side. The 'F' version uses a single eprom from which channel data is read from eight sequential bytes for the receive information for a channel, and another 8 sequential bytes for the transmit information for a channel.

If you just want to re-order already programmed channels, the receive data for channel 00 is in locations 0x0000 to 0x0007, the receive data for channel 01 is in locations 0x0008 to 0x000F, and so on.

The transmit data for the same channels is at (the receive data address + 0x800), so the transmit data for channel 00 is at 0x0800-0x0807, the transmit data for channel 01 is at 0x0808 to 0x080F, and so on.

One further thing to note: The channel select switches (00-99) output a BCD address, which means that when you switch from channel 09 (receive data at 0x0048-0x004F, transmit data at 0x0848-0x084f) to channel 10, you leap straight over 6 unused blocks of eight bytes to get to the data for channel 10, (receive data at 0x0080-0x0087, transmit data at 0x0880-0x0887). This leap forward over 6 * 8 bytes occurs whenever the left digit on the channel switch increases by one.

The detailed info I have seems quite complete, so if you would like it for reference just confirm that yours is the one-eprom version and I will scan it and get it to you somehow.
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Old 29th Oct 2013, 7:15 pm   #10
Biggles
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Default Re: Dymar 1995 PMR set.

Definitely one eprom, a 2732 on the synth board. When I read the original eprom data I saw the gaps and worked out from the logic levels on the address inputs that the channel select switches were BCD. It would have been easier with a circuit diagram though. I would be grateful if you could scan your info for me if you have time. A good circuit diagram and the program info would be ok even if you can't do the whole lot. I haven't tackled the transmitter properly yet but the Rx would be handy to have working on the right channels. Cheers.
Alan.
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Old 29th Oct 2013, 8:08 pm   #11
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Default Re: Dymar 1995 PMR set.

OK Alan - I've got a few A4 pages of text description about the eprom programming format which includes a worked example, a really clean A3 diagram of the one-eprom synth board and a not-great-but-readable A3 copy of the main radio diagram which I think - but can't be certain - is for the later mark that you have.

I'll PM you about this.
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