Monday, December 27, 2010

RXAmp built for 20m.. RTFM next time

Well... all my comments about that your boards should look like they came off a wave came back to bite me on this one.  There is a problem with the kit or current schematic on the SDR-Cube site.. will discuss that later..  The bigger issue for me was that you need to put the three pin connector on before mounting the molded transformer on the board.  Less obvious to me still is that you need to put the 2x2 connector on the top of the board.  Yes, I removed the transformer (with no damage) to put on the three pin using hot tweezers.  Put it in and then remounted the transformer OK.  Then I noticed that I had the 2x2 on the wrong side.  I tried to use the tweezers to remove that and I put a slight scorch in the board.  I discovered that this brand/style of header can easily be taken apart pin by pin and put back together so that is what I did to remount it.  Except for the scorch by L1 the board turned out perfect.  I guess when I build a 40m and 80m one I'll not make those mistakes again.  I guess what I said was to make it look as close as you can to a commercial build!  :O(

The issue with the kit or schematic is that there was no C3 in the SMT parts card and there was an R101.  Referring to the only information that is currently up, C3 is needed as if R101 is supposed to be a replacement it would screw up the biasing of the RF AMP transistor.  The Spinner Household "junque" box stocks 0.1uF (100nF) 0805 caps, so C3 went in and I still have the R101 for future possible rework.

I'm sure this will be cleared up with the assembly manual.  I'll update the post when I know the definitive answer.  I built it to Rev C of the schematic.

Pictures:
Board Top:

Board Bottom:


RXAMP plugged into sr63ng board:

Board with left over parts, R101 (?) and the R7's I didn't choose.  I did choose 18dB gain.. seemed about right.. can always rework it if I need more or less gain:

1 comment:

  1. As was revealed in the build instructions which are on the site now, the R101 is a termination resistor for the filter bank before the input of the pre-amp transistor. Without the proper termination, filter shapes can get pretty *wonky* (technical term) so this should improve perfomance of the RF AMP board.

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