Hi, Elecrafters.
I'm hoping someone can help!
I completed my KXB3080 modification tonight but during testing I
discovered that I am getting pretty much the same transmit power out
(1.8W with 10V) on 40m as 20m (according to the KXAT1 this is the only
watt-meter I have) into a 50 ohm load. I took the board out and
squeezed the green turns on L2 of the LPF1 board together as tightly
as I could and replaced the board back into the case, but it didn't
make any difference I still get the same power out on 40m as 20m. I
understand that this may be an indication that the harmonic
suppression is not working correctly as I should be getting about .6W
lower power on 20m (I certainly was before the mod!)
I placed a scanner across the room (with a 2m rubber duck antenna)
from the KX1 driving a magnetic loop antenna tuned to 7040kHz and
transmitted on 7040kHz. The scanner showed full scale deflection. I
then tuned the scanner to the 1st harmonic 14080kHz and the scanner
'S' meter was maybe 4/5ths deflected.
I know that isn't very scientific, it may be telling me the harmonic
suppression isn't good or maybe it's not. I don't have anything
sophisticated like a spectrum analyzer to do a proper analysis of the
relative strength of the 1st harmonic versus the fundamental.
The LPF1 went pretty much the way the manual said it should. I'm sure
it's getting power as I see a 60mA draw on 80m. The only difference
between my LPF1 and the manual's picture is that my LPF1 PCB doesn't
sit flush to the KX1 PCB because the turns on L1 and L2 extend
slightly past the edge of the LPF1 board. It is about 1mm away from
the KX1 board, but the turns of L1 & L2 are flush to the board.
Does anyone have any suggestions about how I could start tracing this
fault? Should I try compressing the red turns on L2, or the green or
red turns on L1?
Thanks,
Martin.
VA3SIE.
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