Hi
I am strugling with a 2nd harmonic problem into a SO2R set-up.
Set-up is composed by 2 x K3 controlled by MK2R+ machine, W3NQN BP filters
on each radio and monobanders on each band.
Interference problems are from 40m to 20m (2nd H) and this rise up floor
noise level about 60 khz on each side from main harmonic frequency.
On elecraft panadapter the scope shows on 20m that signal is not clean and
it has some more peaks over the band.
I also changed one of the K3's with a different one but no difference.
I have added a double stub W2JVN design on 40M to suppress the 2nd H on 20M
so now I have BPF + stubs.
MiniVNA says the stubs suppression is -65db and the stubs are placed
directly on the 6x2 switch at the 40M output but no reduction of
interference is shown.
Looking at the 20M S-meter it shows 59+30 signal and disconnecting and
reconnecting the stubs there is no difference on the S-meter.
So my first impression is that the signal on 20M is not received from the
antenna outside.
At this point I disconnected all cables connected to radios (except 12V of
course) leaving 20m radio without antenna even.
Now I connected a dummy load to radio on 40M and started to TX with 50W.
Still 20m 2nd harmonic is audible and holding the dummy load by hands the
2nd H intensity is reduced.
What is your opinion on this situation and how to solve?
Tnx in advance.
**** Luca IK2NCJ ****
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