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E-Field AC Induction into Hustler 4-BTV?

Nov 30th 2012, 14:55

w9cw

Joined: Jun 24th 2011, 18:52
Total Topics: 0
Total Posts: 0
One of my antennas at this QTH is a ground-mounted Hustler 4-BTV trapped vertical. It sits over an image plane of 32 radials, and uses a 1:1 line isolator balun at the feedpoint. I have an enormous amount of power line noise here, and in doing some initial testing for the source of the power line noise, I detected something that I've never seen before. I checked the coax at the shack to the 4-BTV with a Fluke 77 DVM, and found over 1.0VAC @ 60Hz riding on the RG-213 coax (measured from the center conductor to the shield of the PL-259). I must admit, I've never checked for AC on any antenna's coax over my decades in ham radio! Next, I connected the coax to my scope, and sure enough, it was 60Hz AC. And, a bit later, I checked it at the feedpoint of the 4-BTV, and it was over 2.0VAC. Our AC power distribution here is on overhead lines and poles, however my service entrance is buried. The power lines are approx. 35 feet from the 4-BTV. Is it possible what I'm seeing here is e-field induction into the antenna? Obviously, I'm measuring this voltage with a DVM and a scope with high-Z inputs, and the level likely may be much lower into a 50 ohm load, such as a typical HF transceiver. I guess one of my concerns is will the AC riding on the coax damage a transceiver, or will the bandpass filters in most new rigs shunt this voltage to ground?
Dec 2nd 2012, 03:10

AA6E

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
It seems likely that you're getting electrostatic coupling from the nearby power lines. A 35 ft separation is pretty small. I hope you're safe against anything falling over onto power lines!

As you suggest, it's probably a high impedance. What matters is what you see across a 50 ohm termination. If you see enough to still worry (i.e., a volt at 60 Hz?), a simple high-pass filter would take care of it. Radios usually don't provide a maximum input voltage spec. (Certainly not at 60 Hz!) They should, of course.

Your AC pickup may well be related to your noise problem, since a lot of HF noise can come in on power lines. If you're lucky, the noise might be coming from some discrete source that you could track down and fix. We'd have to know more about the noise to say much more. Is it constant throughout the day, is it frequency-dependent, is there a modulation? Etc.

73 Martin AA6E
Dec 3rd 2012, 16:29

w9cw

Joined: Jun 24th 2011, 18:52
Total Topics: 0
Total Posts: 0
Thanks Martin. Yes, 35 ft. separation is small, but it's reality when you live on a suburban or city lot, in this case 80 ft wide by 100 ft deep with the house smack dab in the middle. Since the 4-BTV is 22 ft high, there is sufficient separation from the power lines on the back property line in case of a fall. All antennas here are within safe limits of the power lines.

The measured 60Hz AC on the feedline is independent of frequency, and there is no modulation of the AC level - it's constant. The line noise appears to be frequency independent as well, as it blankets everything from 3 to 30MHz with an S-8 level, plus my neighbor's plasma TV has spurs about every 15kHz which, in toto, makes operating even more of a challenge. Maybe in my next life I can live out in the sticks and have acres of land for antennas! Hi...

73 Don W9CW

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