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I've ordered two mini whip antennas from Ebay (Russia) for HF and MW. As power lines cross my city property in a L shape - the only way to get away from them is to go up. So I'm hoping that going 5-20 feet above my roof line will reduce the extreme RFI that is on the power lines.

What is the best option for mounting a mini whip high above the roof?

I'm considering using 10 ft emt. Is it safe to go any higher (say 20 feet) or do I need cables or a tower to do so?

I want to mount two of them so I can phase them. I'm considering using the sewer pipe (which already has a diamond discone), chimney, or gutter/side of the roof.

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  • $\begingroup$ What is the size of your property? Ideally, it would be nice to see a satellite photo of it in Google Maps so we could see exactly where the power lines (etc.) are in relation to your land. Having said that, if you live on a very small lot, that might not help. $\endgroup$ – Mike Waters Dec 30 '17 at 23:06
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First and foremost consider the safety aspects of your intended installation. You should ensure that if the antenna and its supports were to fall, it should not contact the power lines. The same consideration should be given for the installation process to ensure that under no circumstances should the antenna, mast, or cabling nor any equipment used for the installation be able come into accidental contact with the power lines.

Secondly, elevating the antenna by 10 to 20 feet may have a minimal effect on the amount of RFI received from local sources. If the noise source is in the near field of the antenna, then the results can be unpredictable. If the noise source is in the far field of the antenna, then it will basically follow the inverse square law. For example, if the far field noise source is 100 feet away when the antenna is on the ground and you now elevate the antenna by 10 feet, the noise will decrease by less than 1% - an imperceptible amount. Elevating the antenna may help with increasing the amount of desired signal, however, and this would have a positive effect on the Signal to Noise Ratio (SNR).

The question of the mast construction depends on several factors - the yield strength of the mast, the inner and outer diameters of the mast, the height of the mast, and the wind load of the load at the top of the mast (your active antenna system). These factors can be used to calculate if the mast will bend under specified wind conditions and the amount of stress the mounting system for the mast (bending moment at the base of the mast) needs to endure to support the mast under the calculated conditions.

The calculations are rather laborious. I have an Excel spreadsheet that I use in an attempt to reduce the number of errors. For example, I show that with a 1 inch OD mast, 0.1 inch wall thickness, 35 kpsi yield strength, with a 1 square foot of cylindrical wind load at the 8 foot position, the maximum wind speed it can survive is 67 mph (108 km/h). This will have a total moment of > 3,620 in-pounds (> 410 nm). This is the equivalent moment of an average adult pushing as hard as they can on a pipe 1 meter from the mounting point.

If you are interested in the detailed formulas, post back in the comments and I will add them to this answer. Alternatively, you can find the formulas and a spreadsheet here: http://thebont.com/spreadsheets/AnalysisOfAntennaMastStrength.htm

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    $\begingroup$ My entire property is within 20-30 feet of the power line. So this makes it fairly difficult to go that high without creating a structure that could hit it - so that is an excellent point. $\endgroup$ – Aaron Kreider Dec 28 '17 at 22:58
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Vertical antennas depend upon a ground plane to work properly. You could elevate the vertical if you use tuned 1/4 λ horizontal elements (often called a counterpoise) to replace the more traditional ground plane made of radial wires running along the ground. Elevated verticals are often more efficient, but the disadvantage is that you're then confined to a single band.

I think that if you were to elevate a vertical with no ground plane using a conductive mast, then your results would probably be terrible. Your reception of far-field signals, the signals that you want to receive, would probably be terrible, but the near-field signal, that is noise from the power lines, could well be full-strength.

My advice would be to start simply, by trying a single ground-mounted vertical with a proper ground plane. When you know how that works then you can try elevating it, and if you like the results of that experiment, then try phasing the vertical with another vertical.

Trying to receive HF and MW signals from a small city lot with power lines overhead can be challenging. A cheap mini-whip antenna in those circumstances is unlikely to be satisfactory in any configuration, in my opinion. Assuming that you're only trying to receive, in your shoes I think I might try attaching a wire to a guyed fiberglass pole with some sort of air-wound inductor at the bottom, with several long radials running along the ground. (If you'd also like to transmit, then try a commercially-made multiband vertical instead.)

I'd also like to echo Glenn's safety concerns: whatever you do, make sure that your antenna can't accidentally touch the power line under any circumstances. Hams have been killed erecting antennas that accidentally touched power lines.

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  • $\begingroup$ I was doing relatively well with two Wellbrook loops, until the noise level increased 10+ db. I've been avoiding the real solution - canvassing the neighbors, and going through their houses to identify sources, as there are a lot of them (and we also have a lot of turnover of renters). $\endgroup$ – Aaron Kreider Dec 29 '17 at 20:41
  • $\begingroup$ Aha, I thought about suggesting a loop antenna, but I didn't want to get into explaining a bunch of "new" concepts. I'm sorry to hear about your increase in the noise level. That sounds like a sticky problem. Maybe you could try a loop that has a null in the receiving pattern, in case there is a localized source generating the bulk of the noise? Good luck! $\endgroup$ – rclocher3 Dec 30 '17 at 16:49
  • $\begingroup$ The power lines have an T shape on the property. Combined with the re-radiation from the houses wiring makes the loop null less useful. $\endgroup$ – Aaron Kreider Dec 30 '17 at 21:39
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USE SKED 80 PVC UR WINDLOAD IS MINIMAL, BUT I WOULD PARACORD GUY IT JUST TO BE SAFE. IF UR NOISE LEVEL IS HIGH, U MIGHT CONSIDER A PARALLEL COAX FEED [SORT OF LIKE BALANCED LINE, ONLY SHIELDED.] 2 - 50 OHM COAX IN PARALLEL WILL GIVE U 100 OHMS, BUT THAT SHOULD WORK O.K. I USE AN OCFD FED THAT WAY [USING RG-6 75 OHM] AND HAVE MADE ANTENNAS LIKE IT FOR OTHERS. NOTHING BUT GOOD COMMENTS - SOME CLAIM A 5 S-UNIT REDUCTION IN NOISE LEVEL. U CAN SEE IT HERE http://www.hamuniverse.com/kf9focfdipole.htmlTO GET AN IDEA OF THE FEEDLINE. '73 AND GL RICH, KF9F

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