M294 conversion to 4m

Hi all,

I'm looking at converting an old Pye/Philips M294E ex-PMR radio to work on 4m.  The crystal supplier (Krystaly) is asking for some specifications of the crystal;

1) Parallel or Series resonance
2) If parallel, what is the loading capacitance
3) The crystal overtone; 3rd or 5th etc

Although there are many articles still on the net regarding conversion, the only crystal specs I can find are in the Service manual which say "T71" for receive and "T93RX" for transmit along with the frequency calculations.  I am assuming these are Pye/Philips specifications as the above "codes" don't mean anything to Krystaly.

Can anyone help please?

Hi Darran,

You do like playing with your old crystal control stuff don't you.

I can't find the original PYE specifications but the T71 was also AP30 and the T93 was AP29.....I know, not a fat lot of good either is it?

Judging by the schematic for the radio it utilises a typical Colpitts oscillator and going by the maths the receive crystals would be fundamental types and the transmit 5th overtone. Usually in a Colpitts they'd be parallel types with a capacitance of about 30pF but the circuitry uses a series inductor for trimming. Might be worth mentioning that to Krystaly who should be able to advise.

With such an abundance of crystals required to gain each channel (RX & TX) it might be worth taking a look at modern DDS (Direct Digital Synthesis) facilities where you could programme any frequency you want including TX/RX shifts. You might then have to play around bypassing analogue frequency multiplying circuitry etc.

There's always the old fashioned fun way of an analogue VFO, but the shifts and complications involved with that you might as well build a whole radio!


Hope that is of some help......still think you're mad playing around with crystal controlled stuff.

All the best,
Victor

Hi Victor

Hahha, yeah I know I'm mad.  The crystals from Krystaly are only E12 each compared to £50 with another supplier.

I was thinking the same regarding the specs you mention after seeing that the crystals Spectrum has are parallel 25pF/30pF with fundamental for the low values and 3rd/5th overtone for the higher values.  I'm seriously considering taking a punt on a pair of crystals for the 4m calling channel at theses specs. There are only 4 channels on 4m and the radios I have are only 3 channel.  4m seems to be an interest amongst our semi-local club members and is the one band I don't have anything for.

I've got a few M290s here and several more in storage, so I'm itching to put them to good use now that I acquired my MW7 licence at the end of April and about to book my 2W0 soon.  Also plenty of online copies of Ham Radio Today with conversion articles (Not just my missus that can make good use of HRT lol)

Do you know anything about the Eprom programming with the MX290s?  When I first looked at the 15/20 years ago there were loads of suppliers of these radios including brand new PF85 and PFX handhelds still unsold including spare batteries etc.  But all the PMR suppliers seem to have closed down or sold out to other sellers who have discontinued PMR gear.  I literally have no idea regarding the Eproms; whether blank chips, equipment, software are still available or whether that idea is dead in the water?

Cheers

Darran

Hi Darran,

You keep up with the apparent 'madness' as it can be a lot of fun!  

Worth a punt especially if there is band activity within your area or with other club members and always nice to bag another band for the logs. (I don't have any 4m stuff either.) Sounds like you've got fairly clued up with all this crystal stuff and great that places such as Krystaly exist where other manufacturers have disappeared.

Now you've started something with mention of PROM's, EPROM's, etc. and I ain't following you down that rabbit-hole after "bit-banging" EPROMs for radios by hand many moons ago!

I had a quick scoot around and the following handbook is available online with mention of the MX290 series with some details of the program code utilised :-

http://www.radiomanual.info/schemi/Surplus_Civil/Philips_MX-294_mod.pdf

As you mention such activity has all but died off regards such ventures (you used to be able to buy pre-programmed EPROM conversion boards) but am sure if you get your head around it you can achieve something with it all yourself.


Oh, congratulations and well done with your Foundation, I wish you the best of luck with your Intermediate. (Something I should be doing but just having waaaay too much fun with my Foundation! )

All the best,
Victor

Many thanks for that Vic.  I'll clear my brain out and inwardly digest it.

I've sent the info to Kristaly and eagerly await their response.

Yeah, you can have plenty of fun on a foundation.  I've had US, Can and Brazil with 10w on 17m  I'm also enjoying VHF/UHF.  Several SOTAs on 2m and hunting down 70cm repeaters across the border in Angle Land lol.  Something I never thought possible 40 years ago when I initially tried the Class B licence which limited you to "line of sight" VHF and UHF and you needed to pass morse to get on the exciting HF.  I bet there was more activity on VHF/UHF in the 80's; I've had 1 SSB contact in 4 months.

Cheers

Darran

No worries there Darran, look forward to seeing how you get on.

Yeah, went on a couple or so of the old RAE courses back in the day which all got cancelled due to candidates dropping out then a busy life got in the way. To think I could've been a G1 but just glad I was finally able to gain a licence later in life and surprisingly being rewarded with HF privileges. (I think the hobby would've died out had they not made the changes!) 2m activity did suffer but only because operators were forced up there really.

You keep having fun there.

All the best,
Victor