Monday, October 18, 2010

VHF FM transceiver - live tests

IT WORKS!!!

I have now around 700mW output, not the wanted 1W but for now is enough, (I already managed to get 1W but for too much heat dissipation), and I can hit the local repeater with the antenna inside the shack.

video

If you look at the signal meter, the first level, (1/4 scale), is local signal interference and the second level (around half scale) is the repeater signal before it stops transmiting.
I made some audio loopback tests (recording the audo from the repeater transmission) and it looks good, I mean, it's inteligible :)

Now, the world is not perfect and there's still issues/problems to solve:

1 - Place heat dissipators in the output transistors
2 - Sort the problem in the PLL subsystem, sometimes there's no display indication and or garbage and PLL will not lock. Look's like it was a bad solder joint.
3 - There's some delay (half second or less) between hitting the ptt and getting audio via the repeater. Will have to see if it's a delay in the output stage power on and/or PLL unlocking or some delay at the repeater level.
4 - Check modulation level deviation and harmonic generation... will have to study a little bit more on how to verify this!
5 - Make a live QSO.
6 - Finish the project box. Assemble the project box
7 - Put in the shelf....

And now, so that you don't to the same mistakes I did:

1 - Check if your transmit monitor radio is in FM and not SSB mode while doing transmiter tests....
2 - Check if you realy are in the correct repeater tone. I was on the wrong tone and took me a lot of time to undesrtand why the repeater wasn't activated.
3 - Just because when you hit the PTT you listen to some sound on your monitor radio that doesn't mean it's your signal coming from the repeatar. If the monitor radio is close enough you probably are geting a lot of signal localy!
4 - Watch out for loop current's.... in doubt remove the ground connection on any point to point cable.

Stay tuned, for more fun!

Addendum: I can hit the local repeater with the dummy load connected...it's leaking somewhere....

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