Tuesday, July 26, 2016

Transmitter progress

I moved the circuit to copper, but no love.  Still when I turn the bias up, it all goes haywire.  Actually worse than before.  Thinking it might have to do with the drive level, I tried adding an amplifier stage ahead of the 2n3053, but again no love.

Then I thought "hey, I sure have a lot of wires running around here..."  I had been using hook-up wire to join my modules, as I didn't have any extra coax.  But I did get some recently, so I added some BNC connectors to the output of the PA and the input/output of the LPF.  Bam!  Pretty output!

I'm getting 20v P-P on about 11.3V power, which is about 1 watt.  I can get it up to about 1.5 watts by increasing the voltage to around 13V.  But I'm hoping for 5W.  Here at least some of the issue I think is the drive level.  I tried the little amp I had, but I think that was overdriving it.  Was getting about 3W out, but it was well ugly.  Will need to have a think about what the drive level ought to be.

I might at some point see about using a different IRF510.  I've read that "lower quality" parts may not work as well, and I'm not entirely sure about this one.

Edit: actually, after playing around in LTSpice, I think I may need to change out some of the coupling caps.  The ones he uses in the Mighty Mike look to be attenuating things too much.  In the simulation, if I change those to larger caps (closer to .1uf) and run it at the same power he does, I get >5W out, even with my current drive level.  With his values and my current voltage, I get closer to what I'm getting on the bench.

Edit 2 (next day): I tried swapping out the .001uf for .1uf coupling caps as I mentioned in the last post.  Raised the power some, but not nearly as much as in the simulation.  I also tried swapping out the IRF510 for a new one from Mouser, didn't see much change.

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