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G5RV Jr. laying on roof

KC9PYV

KC9PYV

C.B. Rambo
Jun 10, 2009
25
0
11
Would a G5RV Jr. Laying on an asphalt shingled roof be ok? I would probably have one leg a few inches off of the surface of the roof ran straight , but due too the length the other leg would be laying on the roof possibly in a 40 degree "L" shape. I would be running 100 watts. I'm stuck with this option, or the attic next to my 10 meter dipole. Would the antenna on the shingles be a fire hazard? Maybe the differance of being on the roof, or in the attic will be too small to notice. My house is a small ranch with the peak of the roof at maybe 15'. I was also hoping that it would help me with all the electrical noise that I get on the attic dipole, mainly the DVR box for my Direct TV. I'm looking to get on the other bands besides 10 meters. I'm pretty much stuck with this option in this house with the combo of no trees, the wife, small lot with power lines across the back of the lot with the electric overhead into the house down the middle of the yard so low I can jump, and touch it. Thanks in advance for any input.(y)
 

You mean like this? I live in Kauai, Hawaii. Had good Australia Skips and really got out to 144 in Australia. I have the Starduster w/just the main live antenna and one ground plane element in stalled as you can see in the pix. Im getting 1.2-1.3:1 SWR and a 146GTL for base radio and a Pyramid 26Amp power supply.

It should work. As long as you dont have any metal framing along the roofing end.

IMG_0498-1.jpg
 
15minigrass said:
You mean like this? I live in Kauai, Hawaii. Had good Australia Skips and really got out to 144 in Australia. I have the Starduster w/just the main live antenna and one ground plane element in stalled as you can see in the pix. Im getting 1.2-1.3:1 SWR and a 146GTL for base radio and a Pyramid 26Amp power supply.

It should work. As long as you dont have any metal framing along the roofing end.

IMG_0498-1.jpg
Click to expand...

Thats an interesting setup with the partial Starduster. The only metal the antenna would be near would be a couple of sheet metal roof vents.
 
With a G5RV, the problem wouldn't be the sahpe of the two legs of the antenna, or even them laying on the roof. The problem will be in that section of ladder line used in the feed line. It shouldn't be touching, or near anything if possible. That 'nearness/touching' will affect the impedance match. There's no way of really predicting how the match will be affected, so that puts it sort of in the 'best guess' category, sort of.
The antenna laying on the roof is going to make some differences too. Just how much, and in what way is another one of those 'guesses'. If it were possible to sort of 'organize' it's shape, make it sort of 'regular', that tends to make those 'guesses' more uniform, if that makes any sense at all. Laying the center portion on the peak of the roof, and following that to one end, then down gives thigs a sort of 'regular' shape. One leg going down the fron part of the end of the house, then the other leg doing down the back part (sort of a flattened out 'Z'?). See where thats going? And if that doesn't give very good results, re-shape the whole mess! Lots of possibilities.
The only absolutely good advice I can think of for something like this is don't fall off of, or through the roof. After that, things vary a lot.
- 'Doc


I give up. Made more spelling mistakes than I believed possible even for me. The right letters are usually there, just in the wrong places. Not sure what'd do the most good, more coffee or booze. Think I'll try both.
 
Ok, thanks for the input guys. I think it will be some trial, and error for sure. Hopefully I can find some kind of common ground with this setup until I move. As for the ladder line feed line, I can't remember the brand of antenna I bought, but it has a flattish type feed line that doesn't look like true ladder line. I don't know if that helps me any, or not. Maybe it's not a true G5RV? This stuff is pretty new to me.
 
There are a few other wire antenna designs that be easier to get working than the g5rv. Like 'Doc said, the biggest issue will probably be the ladder line matching section. You may have no problem or you might have a big one. This is one of those deals where you're going to have to try it and see. The ladder line is supposed to be perpendicular to the wire, so I have a feeling that it's not going to work well...in other workds, you may get it to match but not be able to hear much.

How about just using a 40 meter dipole? If you can fit the G5RV Jr. on your roof, you should be able to fit that. Or even better, what about a 40 meter loop laid on the roof? You'll probably need a tuner for both of these ideas.
 
moleculo said:
There are a few other wire antenna designs that be easier to get working than the g5rv. Like 'Doc said, the biggest issue will probably be the ladder line matching section. You may have no problem or you might have a big one. This is one of those deals where you're going to have to try it and see. The ladder line is supposed to be perpendicular to the wire, so I have a feeling that it's not going to work well...in other workds, you may get it to match but not be able to hear much.

How about just using a 40 meter dipole? If you can fit the G5RV Jr. on your roof, you should be able to fit that. Or even better, what about a 40 meter loop laid on the roof? You'll probably need a tuner for both of these ideas.
Click to expand...

I bought this antenna to mainly get on 40/20. Would a 40 meter dipole be any good on 20? I already am stuck with this one for now, so I'll see how it does like this. If It gives me too much of a headache I will sell it, and start over I guess.
 
Would a 40 meter dipole work on 20 and 40 meters? Eh... not real good on 20, but probably as good as that G5RV on 40 meters, sort of. A 40 meter 1/2 wave is almost a full wave on 20 meters. So, if you wanted to have a good 40 meter antenna and a so-so one on 20, it would certainly work. Using a 75 ohm matching line with the normal 50 ohm feed line would/should get the SWR down to a reasonable match on 20 meters. It would mean swapping that matching line in/out when changing bands though, so not exactly the easiest thing in the world. If you have a tuner, forget that matching section and just use the tuner.
A 40 meter 1/2 wave dipole is right at 65 feet 5 - 6 inches long. You'd have to trim it to length for best match on 40 and just leave it as is for 20 meters. I don't know about you, but I'd certainly build my own before buying a dipole, they are not difficult at all. About 70 feet of wire, maybe three insulators, and some coax. Almost any plastic can be used for insulators so making them isn't difficult either.
I would recommend not just laying it on the roof. Doesn't have to be very high, a couple'a few inches would work. What are the chances if a couple of short boards on the ends of the roof ridge, and maybe one on the bottom corners of the eves? That's get it up off of the shingles. 1" x 1"s or 2" x 2"s for those boards, whatever size would hold the thing up. H#$$, make'em 6 feet tall and put bird houses on top of them! Whatever works, you know? "Oh, that wire? That's so they won't fall down."... amazing what neighbors will believe sometimes. (That's called community relations, by the way.)
Lots of possibilities, just takes a little imagination sometimes...
- 'Doc
 
Huh... why didn't I think of that. You stole my idea Beetle, shame on you. ;)
- 'Doc

Dang, while we're at it, why not add on a 10/11 meter?
 
Why don't you make a fan dipole using coax, that would solve the ladder line problem. you just cut one dipole for 40m and one for 20m and connect them to a center connector, this way the 40m could be in a sort of V configuration on one side of the roof and the 20m same way on the other side and the coax should give you minimal lose. shouldn't be hard to make and cheap.
 

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