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G5RV Configuration Question

Dec 20th 2013, 23:22

Steffen

Joined: Mar 9th 2012, 17:06
Total Topics: 0
Total Posts: 0
I live in an apartment building and want to put a G5RV on the roof. I have to keep the entire structure out of view from the street, and also avoid running coax on the roof surface. These restrictions necessitate my taking a bit of liberty in the placement of the G5RV.

The roof is about 60ft above ground. I do not intend to invert the G5RV, but rather support both ends by stringing them up to two convenient tie points on the roof. My main question concerns the 31ft 450 ohm ladder line matching section. I read that the ladder line should come away from the flat-top at a right angle for at least 15ft. Can I run the ladder line down the side of the apartment building brick wall and near a fire escape, or will the brick wall negatively effect the intended properties of the line? Furthermore, can the antenna be about only 5ft off the surface of the roof and still give good performance?

Thank you - KA2KNX
Dec 21st 2013, 11:40

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0

It is likely that 5 ft above the roof is an OK compromise--slightly stronger signals with better height, but you don't really have that option.

On the other hand, you really do need standoffs for the open wire line--you can expect a significant signal loss when run up against brick or concrete.

A much better option is to run a short length of open wire to an automatic antenna tuner through a good choke balun, and then coax all the way to the shack. You might need to experiment to avoid core heating/SWR drift on one or more bands.The balun is more for antenna efficiency that feedline decoupling--chances are, your feedline will be plenty decoupled by that brick and concrete.

Zack Lau W1VT
ARRL Senior Lab Engineer
Dec 21st 2013, 13:28

Steffen

Joined: Mar 9th 2012, 17:06
Total Topics: 0
Total Posts: 0
Thank you for a very complete answer. I will work on this and report back. Once again - just what I needed to know!

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