Ground Loop "Hum" Using BT Modulator

[zenith2134]

Regarding RF reflection back into the transmitter: When using an impedance-matching balun( which is essentially a transmission-line transformer), not all emitted energy gets relayed to the antenna. Some gets sent backward into the final stage. This causes less output power and heats up the rf amp more. That is my understanding of it, anyway.
Remember, these agile modulators, as originally used, fed coax cable distribution networks which were a solid 75-z load.

[vts1134]

Tried a direct connection from coax to dipole leads, as well as increasing the coax feed length to 70+ feet, both to no avail.

Originally Posted by zenith2134

On one of my B-T AM-60-550 units, I had a rolling bar which was antenna-dependent. upon installation of a proper coax run and dipole antenna, the issue went away 100 percent of the time. Prior to the antenna switch, I was using an F-connector-to-300 ohm balun and I figure that's what caused it.

Can you tell me exactly what antenna setup you have? Maybe there's something small that I'm overlooking.

[zenith2134]

8 feet of RG-6 cable terminated into a Yagi antenna, with the shield mounted right the base element. It is hidden in the attic. The others have simple dipole antennae. I run 3 channels all VHF

[vts1134]

I'm at my wits end! I've swapped antennas, swapped sources, killed 100% of the power to my entire home except source, modulator, and monitor, I've removed my cable input to the house, I've replaced the 4 main filter capacitors on the modulator power supply. I don't know where to go next other than to hard wire the modulator to all of my vintage sets (no small feat at all!!!!). There has got to be something I'm missing.