Ground Loop "Hum" Using BT Modulator

[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.

[old_coot88]

Did you try unplugging (not just turning off), one by one, every appliance and electronic device in your domicile? Often this can identify the source of the hum.
But if you live in an apartment with adjoining units, this won't help if the source is in another unit.

[vts1134]

Originally Posted by old_coot88

Did you try unplugging (not just turning off), one by one, every appliance and electronic device in your domicile? Often this can identify the source of the hum.
But if you live in an apartment with adjoining units, this won't help if the source is in another unit.

I did unplug the other items on the same circuit as the modulator, source unit, and test monitor to no avail. This is a really great suggestion though. I remember going on a service call for a CD player and amplifier that had static noise in the background. I never heard static quite like this before and after swapping out the CD player and getting the same results I started unplugging things. It turns out the problem was this machine that "created ozone for therapeutic purposes". It looked like a quack device to me (this was a boutique beauty salon). The machine created this interference even when it was turned off! It was a great learning experience for me and I remember it every time I have a problem (work or hobby).

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.

This has to be the problem. When I connected the modulator directly to the TV before I was simply paralleling off of the antenna directly to the TV, which as I said before didn't solve the symptom. This morning I took the antenna off of the modulator all together and did a straight connection from the RF output on the modulator into a matching transformer to my test monitor. Absolutely clean signal with no hum bar . I will experiment with different antenna setups to see what configuration gives me hum free operation.

[zenith2134]

I haven't had my agile modulators apart, but I reckon that the hum-bar is some type of RF reflection back into the final stage, which certainly should be avoided. If these were higher power transmitters, any reflection could theoretically smoke the final RF stage.
However I am not certain that this is what's happening.

[vts1134]

Can you elaborate a little bit on RF reflection into the final stage? I would like to learn what that is.

BTW I'm using a run of RG6 about 15ft long run from the RF out on the modulator into a matching transformer set on 75ohms to a pair of 16ga wires approximately 43 inches long each. Could a part of my setup be causing RF reflection? I'd love to have an antenna analyzer to fine tune my dipole, but I don't have that in my bag of tricks. Maybe I could find a ham guy here in Pittsburgh to help me out.