[Elecraft] KX1 20mtr tx okay but no 40 mtr tx

[Don Wilhelm]

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.
>
>