Now output

Everyone who commented to my last post about the lack of output from the Kits and Parts RF amp felt that the problem had to be the QRPer’s curse – the toroid inductor. Normally I don’t have a problem with toroids, but when they are so small that your thumb obscures the whole core while you are holding it, never mind winding it, they are not the easiest of components to work with.

So I gritted my teeth, tried to forget the hour I’d spent yesterday wrestling the thing into position, and yanked it out. One of the wires broke off in the hole leaving nothing to grab on to. I was unable to clear the small plated-through holes in any case. What I was able to do was melt the solder enough to push some bare wire through, creating “pins” that I could solder to. I twisted together the two wires that are connected so I had three ends to solder to the three pins I created. The toroid now stands up on the board a bit but it was easier soldering to the pins than trying to get four thin wires to go through four holes simultaneously. To my joy, on applying power and RF the power meter showed output.

I’m getting about 150mW if the amp is supplied with the recommended 8V, and just about 200mW from a 9V supply. That’s only about 10dB of gain, a bit less than expected but probably enough given that the Propeller does not generate the purest of signals. The WSPR beacon has already been spotted a few times in Germany. But the 2N5109 runs a bit hot to the touch so I’ll have to QRT until the heatsink I ordered arrives. In the meantime I still have the LCD UI board to assemble and play with.

Julian Moss, G4ILO, is a regular contributor to and writes from Cumbria, England. Contact him at [email protected].

One Response to “Now output”

  • W0FMS:

    10 dB isn’t all that bad for a power device.. it might be 2-3 dB low, or it might just be that device.

    As for running it in the mean time.. if you have a little bit of brass, copper or aluminum you can make a dandy fine heatsink by bending a strip around the device and leaving a good sized tab. Good to see you have it working.

    I’d also suspect once properly heatsinked, that you could run even more than 9V into it..

    73 de Fred W0FMS

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