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a semi-old, mildly grumpy, damn lazy new General Class Op, back after nearly 40 years since last license.

Live in an old 2 story Mediterranean Sunset District Avenues home with a flat, beam-bitumen-tar-gravel roof with a rectangular 50x24' dimension, no or very little metallic obstructions.

I could place a G5RV Jr at opposite long corners, ladder line feed lying horizontally perpendicular to the "dipole", with a 45-50 run of coax to my second story window.

I could raise it up a smudge if it would make a significant positive impact. I work mainly PSK on 20/40 20-25W and 20/40 SSB.

I run a 756PRO and have a nice tuner they have been workhorses during the last two years of remote deployments. I'd like to get back to CW ops as well. I'm looking for the most bands and bandwidth I can get, with as little noise as possible(like everyone else).

I am also likely the most technically ignorant modern Ham around. Hence, this will be purchased, not constructed and I like the build of the ARS G5RV Jr with terminal 1:1 Balun, for our salt air.

I'm retired/disabled ex-military, sharing a house, on a fixed limited income. I'm going to get one day worth of roof access with help, so "optimal placement" first time is hoped for.

I suspect almost anything will do better than my current poorly placed Euro-Comm Vertical mounted on my window ledge on a cable dish j-pole mount (seriously), only 12' of which is truly above roof level and the coax run to my rig is about 8', air choke hanging off the ledge.

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    $\begingroup$ Hi Rich! Well, I took the freedom of adding a few paragraph / line breaks to your question, to make it easier to read for the crowd :) Wish you the best for your project; sadly, I'm not experienced enough to help you out directly. $\endgroup$ – Marcus Müller Aug 4 '17 at 13:37
  • $\begingroup$ Are you saying the entire antenna would be laying flat on the roof? $\endgroup$ – Phil Frost - W8II Aug 6 '17 at 12:06
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A G5RV antenna is a dipole with an impedance-matching ladder-line feed stub, with the dimensions of the wire and the ladder line carefully chosen to provide a low SWR on many bands. (Please note that there are bands where G5RVs and variants perform terribly. A G5RV is not an all-band antenna, it's a many-band antenna.) A transmatch, aka antenna tuner, is usually necessary to get the SWR below 2:1. A 1:1 current balun should be used between coax and ladder line.

The design assumes that the ladder-line feed stub is perpendicular to the dipole wires, and in free space not near any conductors. So what happens when the ladder line is lying along a roof? In the best-case scenario, there won't be anything metal near the ladder line. In that case, I would think that the antenna would be detuned somewhat, because the dialectric constant of the roof is different than that of air, which will make the SWR of the antenna somewhat higher. Higher SWR would result in less power out because the efficiency of the coaxial cable and the transmatch will go down.

If there is a significant amount of metal nearby, then that metal will effectively become part of the antenna. That could have lots of effects; I would think that the antenna would be more severely detuned and the efficiency of the antenna would go down because metal plumbing or wiring in your house was not designed to be a ham antenna.

Like Jon said, the usual ham approach to the problem is to try the antenna and see how it works. Even if it's not as efficient as a G5RV up high with the ladder line in the clear, you could still make lots of contacts with such an antenna. Be warned though that having the antenna close to the house could result in other problems, like RFI or RF in the shack. My advice is to raise the antenna up as much as you can; if you could raise the ends of the wire even just a few feet above the roof, then the antenna would probably perform better than one laying on the roof.

Good luck, and have fun!

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Rich:

Like most things with antennas, there's never a definite answer. In most cases you just have to try it. I can give you some information from my experience.

My first antenna was a G5RV hanging between two trees on the side of a hill barely 10' off the ground. The ladder line was on the ground for most of it's length, which is suppose to be bad since the line works best when away from obstructures (especially metal). Despite this, the antenna worked well, and my very first contact on PSK31 was over 7,000 miles using just 30 watts. I had many other good QSOs with that antenna before I upgraded to a full size multiband vertical on top of the hill. An antenna tuner can compensate for imperfect placement to some degree.

Just an idea....what if you hung the antenna diagonally from the corners of your roof as high as you could get it (even if that was only a foot or two so it wouldn't be sitting in a puddle during rain), then stretched the ladder line out diagonally as far as possible to one of the other corners? That should reduce interactions with the roof so more of the signal would radiate out where it could do some good. Just a thought.

Good luck, and 73,

Jon, K0ARG

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  • $\begingroup$ Hi Jon, and thanks for your answer to Rich's question. Welcome to ham.stackexchange.com! $\endgroup$ – rclocher3 Aug 4 '17 at 18:15

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