>From the description of your test:
1.) No TVI on dummy antenna
This means you have no power line or chassis radiation problem.
2.) No help from low-pass filter
This means the harmonics are generated outside the radio.
3.) You measure the harmonics on a spectrum analyzer. I assume it is a good
unit and not being overdriven. The harmonics only bother the X3 fundamental
of the transmitter in the video signal only.
This again points to harmonics, and not overload inside the TV set.
I can suggest a few things for you to try. The first is to know that
everything is not absolute, and there may some wrong information, but the
most likely thing is harmonics generated outside the radio.
Since that is a very difficult problem and you have not tried one more
obvious easy thing, I would do the easy even if unlikely to help. I would
install a good high-pass filter on the coaxial line to the TV set right at
the TV, and GROUND the shield of the TV cable to the electrical safety
ground of the AC power outlet for the TV set. I am pretty sure you have a
safety ground available at the outlet.
What this does is make sure you have no RF inside the cable and no RF
following the shield to the TV set and flowing through the TV set to the
If that simple addition does not work, you will have to get a small yagi
antenna at 63Mhz and a portable receiver and look for the source of the
harmonic. Most HF radios now have VHF harmonics more than 55dB down, and
very tiny case and power line radiation. Most likely the harmonic is being
generated in something like a small iron core (a TV antenna or feedline
balun), a poor metal to metal connection near or in the antenna, or other
semiconductors near the antenna. Perhaps you can turn the TV antenna while
watching the harmonic level on the TV antenna and see the direction?
Please let us know the results of more testing or experiments! You have an
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