[CQ-Contest] So2r strange 20m harmonic signal showing from a 40m tx

[Jeff Blaine]

In working up the So2r config here, I’ve run into a strange and very wide 20m harmonic off a 40m CW signal.

The rigs are a pair of FT-5000 and FT-2000.  Although both rigs TX will give the effect...

Two things are strange about the 20m harmonic...

First, the signal is about 15 Khz or more wide although it tapers to quite a broad bandwidth lifting the noise floor out at least 30 Khz either side.  When you hear it, it does not have a pure note as you would expect from a typical harmonic.  And on the spectrum analyzer, the signal is confirmed actually being this wide in reality.

Second, the signal is confirmed to come from the TX.  It’s not rig to rig or coax or other leakage path.  Yet despite this, it seems I cannot filter the signal!  

Enabling the 40m BPF filter seems to give no attenuation to this signal.  I have 2 different sets of W3NQN style filters here which test on the VNA with excellent attenuation (>40 db) of the 20m signal when in the 40m position.  

The same effect has been observed by another gentlemen on his M2 station based on a pair of FT-5000 today.  So its not a unique situation to my install apparently.

I’m hoping some more seasoned So2r or M/M guys would have more experience with this and know what the “fix” is.  It’s driving me nuts.  ha ha.

73, Jeff ACØC
www.ac0c.com