Antenna ground loop hum

Posted by Richidoo (A) on January 18, 2007 at 18:27:59

I put my radio shack yagi FM antenna up on the roof this weekend. It was playing nicely before I raised the antenna (and grounded it). Now I am getting a hum. I have the antenna mounted on a gable mount with a 5 foot steel pole.

As for grounding, I have a solid copper 10ga ground wire connected to the ubolt holding the antenna to the pole. This ground wire then connects to the ground terminal on the lightning arrestor about 40 feet away where the coax enters the house. The ground wire is split at the arrestor with two heavy copper lugs. It then continues on to the main house ground rod at the electric meter, about 20 more feet away.

When I remove the antenna ground wires from the arrestor, and connect them together and run it straight to the ground rod, then the hum stops. But I know the arrestor must be grounded.

I have learned today that I need to connect the ground much better to the mount using a pole clamp, and also that the mount ground wire should be continuous with no splicing, so I will have to redo that. Should the antenna element itself be grounded, or is its teeth digging into the mounting pole sufficient connection? Is grounding the antenna element AND the coax the source of the hum? Maybe I should just be grounding the mounting pole, but the antenna and the pole they are electrically connected anyway by the teeth on the antenna ubolt.

I have a Sansui TU-717, modified by Stereo Surgeons with a 75ohm input connector. This connector also has two small threaded screw holes labelled ground right below the F connector, but I have nothing connected to them. The tuner has a 2 prong plug.

I have all plastic piping.

Since the hum sounds like AC power, I was thinking I could just bury a new ground rod for the antenna mount ground and transmission line ground. Should I connect the antenna mount ground wire to that separate ground rod too? It seems that if I bond a new rod to the main house ground rod the hum would go into the coax and start the hum again.

Burying a new rod for FM antenna only would be fine with me. Is the rule for single ground rod per house only apply to electrical service?
Thanks for any advice
Rich

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Topic - Antenna ground loop hum - Richidoo 18:27:59 01/18/07 (4)

Solution. - Hepcat 15:35:05 01/20/07 (3)

Re: Solution. - Richidoo 05:35:43 01/21/07 (1)

It works! - Richidoo 12:17:34 02/04/07 (0)

another cheap solution possibility - bartc 16:16:53 01/20/07 (0)

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