[TowerTalk] Bandpass Filters

[Mark]

I have found that with my 50 ft tower bracketed to the house, with both the 
20 and 40m antennas on
that tower, I get enough 40M signal radiated into the house wiring that the 
20M harmonic is both emphasized
as well as heavily modulated with 60hz products, to the point that it was 
impossible to work any but the
strongest stations on 20M within 15 khz of the 40M harmonic.

With some troubleshooting (ie flipping off breakers while viewing the 20m 
signal on a spec analyzer) the
worst offender was found to be a Samsung cellphone charger plugged into an 
upstairs outlet.  Unplugging
it reduced the harmonic on 20M by over 20 db.  Putting ferrites on the ac 
lines going to the second story
rooms nearest the tower also aided in reducing the level as well as the 
modulation products.  A positive side
effect of all this was a general reduction in noise level on receive.

So second harmonic spurious can exceed the calculated levels because of 
generation by external means as
well as improper filter termination reducing expected filter response.

The 40M signal went through a dunestar filter, and coaxial stubs, while the 
20M signal used an ICE 419 filter.

(also I was careful to ensure that what I was measuring was not the result 
of analyzer overload, since that can
also cloud the measurements).

Mark n2qt