ARRL

KO0Y

Joined: Sat, Apr 7th 2012, 19:22 Roles: N/A Moderates: N/A

Latest Topics

Topic Created Posts Views Last Activity
Ground Plane antenna near metal roof? Jul 6th 2013, 15:28 4 704 on 9/7/13
Does paint affect a Yagi? Jan 17th 2013, 02:40 4 613 on 25/1/13
50 or 75 ohm reference for analyzer? Jan 6th 2013, 22:52 2 582 on 7/1/13
Using ladder line with Yagi Jan 2nd 2013, 00:58 1 623 on 2/1/13
Two new ham questions about antennas Dec 9th 2012, 16:56 7 1,245 on 26/12/12

Latest Posts

Topic Author Posted On
Ground Plane antenna near metal roof? KO0Y on 9/7/13
Quote by W1VT

For lightning protection, you need to be aware that lightning coming in via the power lines will often seek out the shack ground--it is best if it can do so external to the house--hence the NEC requirement to bond everything together. I'd make the feedline as long as necessary to keep the ground wires straight.

Zack Lau W1VT
ARRL Senior Lab Engineer


I put the antenna on a painter's pole and stuck it out the upstairs bedroom, about 2 feet above the roof, and the SWR was around 1.1-1.3 on both VHF and UHF-better than on the deck! So I guess it will work.

About grounding: I plan to run a #8 bare copper conductor from the antenna's ground-plane side to the 8 foot copper rod that also serves to ground the HF antenna and shack (each on a separate conductor). Should I use plastic for the antenna mast or would it matter? Should I leave the roof ungrounded or should I run another #8 from the roof in a different location (straight down to the grounding rod)? The antenna ground will have two bends to reach ground: 30 then 60 degrees. Is this acceptable or should I connect the antenna to the roof and depend on the roof's straight grounding conductor? Thanks again for guidance. I want to get everything straight before I rent the 32-foot ladder needed to reach the roof peak from the surface!
Ground Plane antenna near metal roof? KO0Y on 6/7/13
I have an Arrow 2 meter/70 cm ground plane antenna (model GP 146/440) that I have been using as a portable, but now want to mount on a mast at one end of the peak of a 3:1 pitched roof. It is a metal roof, and is not grounded.

How far above the roof should the antenna extend? (Lower would be better from a stealth perspective.) Would the metal roof add to or adversely affect the ground plane? Does it matter, to the antenna, whether the nearby roof is grounded? We live in a Colorado park, that is, a small circular valley surrounded by peaks, including one directly north and towering 300 feet above us. Hence, I have been more concerned about surge currents than a direct strike. The antenna will be connected to an Alpha-Delta transi-trap, which is grounded via earth rod.

I have been using a Yagi placed in the trees above the house (but well below the peak) and pointed southwest. But I've noticed that the ground-plane, when placed on a pole on my south-facing second-story deck, gives much the same coverage, without the 150 foot feed of the Yagi. This location is 20 feet below, and 10 feet laterally, from the roof.

Thanks for any guidance in this.
Does paint affect a Yagi? KO0Y on 17/1/13
Thanks; I did not know EZNEC would do that. I've covered the feed point with that sticky coax seal, and we live in a dry climate, so that should be OK. I should have mentioned that the antenna is a 3 element 2 meter Yagi.
Does paint affect a Yagi? KO0Y on 17/1/13
I put up a small Cushcraft Yagi, and it does what I wanted. I'd like to spray paint it with a Rustoleum green to make it less conspicuous among the trees. Would that affect its performance? I would not paint at the feed point, of course, just the mount and elements.
50 or 75 ohm reference for analyzer? KO0Y on 6/1/13
I bought an antenna analyzer to scan my dipole's SWR. It can be set for either 50 or 75 ohm reference impedance. The initial line is 50 ohm LMR-400 coax, but that connects to a 4:1 balun, then 300 ohm twin line to the antenna. 300 divided by 4 is 75, so should I use 75 or 50 as the reference? I get significantly different results when changing. Thanks.

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