That condition is often associated with a problem in the DDS low pass
filter. The result is that there is a lot of harmonic content in the
transmitted signal. On 20 meters, the output low pass filter takes care
of things, but on 40 meters, it does not. If you look at the 40 meter
signal with a 'scope, you will see a distorted waveform rather than a
clean sine wave.
Check L4, L5, C50, C51, and C52 - if the values are correct, reflow the
soldering with a hot iron (750 degF) and add a wee bit of solder to get
new flux on the connection.
Also check to be certain that U1 is fully seated into its socket - the
narrow part of the pins should be completely into the socket. It takes
a good bit of pressure to accomplish that. Put your thumbs on the IC
and your fingers under the board and apply pressure until it is seated.
73,
Don W3FPR
On 10/3/2011 8:57 PM, Jeff N3FYW wrote:
> I am in the process of completing my KX1 assembly and testing. Everything
> has been working out fine until I was doing the transmission test. With a
> factory transceiver nearby, 20 meter test works fine; 40 is a bust. A good
> signal is heard at or about 14.100 mHz; none at 7.100 of anywhere on the
> band. 40 receives perfectly. So, any suggestion where to look would be
> appreciated. BTW, the toroids were purchased pre-wound and verfied before
> installation, but don't let that affect suggestions. Thanks in advance.
>
>
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