On 12/5/2021 4:47 PM, Mike Wetzel wrote:
I have been fighting a bad 2nd harmonic problem for a number of years mainly
from 40 to 20 meters. A few years ago a double stub on 40 only reduced the
2nd harmonic about 15db so I thought something else was going on.
Hi Mike,
In addition to the rotators, W3LPL, who was the first I heard bring this
to our attention, also reminded us that non-linear devices anywhere near
TX antennas can be creating the intermod that produces the harmonics. He
observed that SMPS are notorious for this. Suspect any power control
electronics -- stuff in your home or in neighbors' homes. The two of you
may be able to DF while you rotate TX antennas to excite the sources,
and the RX to detect them.
These intermod generators are everywhere -- several years ago,
W6GJB'scontesting trailer was set up in a National Forest in a
relatively remote part of the Sierra Nevada. Glen and I have made it
super clean of issues, but we encountered massive intermod. The
possibilities -- a cell site at 500-1,000 yards, the RV owned by one of
our team members, other campers parked along the access road by which we
reached our site. Several years ago, I witnessed the problem on a brief
visit to W7RN, listening with a second set of cans next to N6TV running
SS CW.
73, Jim K9YC
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