Batboard

I've just got an old Business dispatcher model D31BMT and I'm looking to get it going on 6mtrs, but I don't have the crystal formula and tune up details. I've searched the internet but the only info I can find is for the High band VHF model.

Can anyone help me with the info I need?


Thanks
Dave g1jwg

i have a manual for this D31BMT which is like new and it states that tx crystals are transmit fo=fc/12 and the recieve is a little more difficult:

reciever frequency calculations fc= carrier frequency (25-50)
fo= oscillator crystal freq. (24.545 - 49.545 mhz)
f1= IF frequency (0.455 mhz)
ftr= trap frequency (24.090 - 49.090 mhz)

fo = fc - f1
fc = fo + f1
ftr = fc - 0.900 mhz

I had to look the data up, and Captainp51d beat me to it.

Receiver crystal is a AM-12 and the transmitter is a ZNN-3A. International Crystal can make them for you but you are probably looking at about $ 20 per crystal before shipping fees.

It is important to know which range the radio is. Namely: 25-30, 30-36, 36-42 or 42-50 MHz. Only the 42-50 range will retune to 6 Meters without grief. The others require modifications. Considering this radio is over 40 years old, it is probably a waste of effort to consider a range change job because of the work involved.

The receiver design does not use a separate IF oscillator, and is a bit unusual. Alignment is not trivial and requires the usual steps with the addition of alignment of the image traps. And, more work than that, if the receiver has the extender (blanker) option. The alignment section of the manual consists of several long fold-out pages, and expects you to have an S-1056 or equivalent test set, although it can be done without one.

Thanks for the quick replies with the Info.

I believe it is the high end of the band but not a problem if not. I got it as a nice addition to my radio collection which is mainly British PMR sets from the 60's and 70's and is unusual for the UK as there were no allocations for PMR use in that part of Low VHF, only military who used home produced sets. Our Low VHF used by PMR you call mid band 68-88Mhz.

This one is probably ex USAF having come from an airfield as it has a sticker indicating what you can do when the runway crossing lights are lit in different combinations and a callsign of Medic 07.

So a radio with an interesting historical background for me to play with, probably not worth the effort but if it was easy I wouldn't enjoy it half as much even if I never get it going.

Is there any obvious indications of what part of the band it will be on?

Regards
Dave g1jwg

You can tell by doing the math on the crystals. If the crystals are missing, look for part numbers stamped on the chassis somewhere in black ink. Look for a number beginning with TUB- on the chassis or one beginning with NRB- on the receiver, post the numbers back here and I will translate what they refer to.

Most military low band radios used on airports were in the 40 MHz range, thus this may be a 36-42 MHz range radio. You can move it to 6 Meters but it will be a lot of work and you will need to buy a manual somewhere.