Monday, 16 November 2015

Pye PF8 Conversion - Partial Success

With the new 70cm SU20 channel crystals in hand, I found time today to work on the conversion of the Pye PF8 to 70cm. Earlier efforts resulted in me effectively buggering it up, due to not following the procedure properly, and by not appreciating that modern crystals have just a pair of insulated lead outs rather than the whole base of the crystal being an insulator - with the result that I shorted the bloody thing out! I also inadvertently put a little more voltage on it than it likes, luckily it seems not to have killed anything, although I cant be certain yet!

With thin slivers of polythene cut and fitted as insulators under the crystals, I started the tune up. It was here that I hit a major problem. L13, part of the Tx chain, was broken. Both the ferrite core and the coil former were shattered. Replacing it required a complete strip down of the set, and some very careful desoldering and soldering. L13 is the 2nd can from the left below, shown after replacement.

And the original, knackered coil -

Since I had the whole thing apart, I also took the time to replace the lower microphone housing, which was split around the threaded insert.

I also removed C69. This capacitor is only needed when the Tx and Rx frequencies are more than 4MHz apart, but of course im converting this to simplex!

After following the official alignment procedure (mostly!), the set is now working on 70cm, admittedly though not as well as i'd like. For a 500mW set, if so far managed to coerce a mere 50mW from it. On receive, after a lot of fiddling ive got it to work at -85dBm, a far cry from the -118dBm im used to setting PMR squelch pots at!

Before I look at improvements based on trying to convert the U0 band (440-470MHz) components to T1 band (405-440MHz), I want to check that my lack of success is to be expected, and not the result of another fault somewhere.


Jordan said...

Really interesting to watch you work like this! Hope you keep working on this - you've done a great job so far. Thanks for sharing!

Zak The Rabbit said...

Thanks. Just waiting for free time to fault find. I have to go very carefully since I have only one set of spares