View Full Version : New GP antenna, insulate from Mast?

05-05-2013, 12:13 PM
I recently moved my radio shack from my motorhome into my house. I mounted a 4 foot piece of EMT pipe to a vent pipe on my roof and attached the antenna. The antenna is an Arrow GP 144/440. It looks like a J-pole with radials pointed down about 45 degrees. I used tie wraps to secure the RG-8X coax to the mast. My radio is a Yaesu FT-1900 mobile.
I am getting out fine to the local repeater which has perfect line of sight. Using the radio for simplex is interesting. I seem to be getting out fine except that when I check in on a Net, I am able to get a good signal from all except the Net Controller. He is about 5 miles southwest. Another station responding is another 2 miles away and also southwest. I can read him full quieting, great signal.
My question is, mounting the antenna to a metal mast that is probably grounded thru my sewer line causing me lose of signal? If so, how can I insulated it? Also, can turning the antenna with the J-pole section a certain direction help?

05-05-2013, 04:45 PM
I used PVC split in half to insulate mine. I was mounted on an inch and half pipe so I split a 2 inch piece of pvc and it works fine. The J pole may be a little directional, but probably not much. Wouldn't hurt to check it with a FS meter.

Andy N1ORK
05-05-2013, 04:48 PM
Usually the mounting of the antenna is at ground level because the ground for the coax is connected there. So, you should be ok on the vent pipe. The radials are also at ground, so there should be no problem there. Depending on what is between you, how much power you run and the net control 5 miles away may be an issue. I assume he is listening to you simplex on the input of the repeater. I don't think you should insulate it and turning the j-pole may not make any difference.
Post a photo so we can see what it looks like.
73 and good luck!

05-05-2013, 08:10 PM
Here are some photos of the antenna and pole. I spray painted the pole black.
http://im1.shutterfly.com/media/47a3db24b3127ccef35f5263524a00000030O02AZN2bZo4cMQ e3nwQ/cC/f%3D0/ls%3D00100884637220130505233616450.JPG/ps%3D50/r%3D0/rx%3D550/ry%3D400/
As you can see it looks like a small J-pole.
http://im1.shutterfly.com/media/47a3db24b3127ccef35e9bbeb31700000030O02AZN2bZo4cMQ e3nwQ/cC/f%3D0/ls%3D00100884637220130505233632770.JPG/ps%3D50/r%3D0/rx%3D550/ry%3D400/
Only running 50 watts at most. It's up about 20-25 feet off the ground. Coax runs across roof, under eaves, down exterior wall and under the house 3 feet.

05-05-2013, 09:37 PM
It's a ground-independent antenna, so insulating it from the mast, or not insulating it from the mast, ought to make exactly no difference at all.

05-05-2013, 09:54 PM
Can rotating the antenna improve signal?

Andy N1ORK
05-06-2013, 06:07 AM
Can rotating the antenna improve signal?

It may, but may not be worth the trouble. I have an Arrow 2/440 j-Pole (without radials) and it makes no difference.

05-06-2013, 08:49 AM
Thanks Andy. We don't get much lightning here where I live and I'm some what low compared to other structures. Since the antenna is attached to the vent pipe going right thru the middle of my house, I should probably install some sort of lightning protection. Any suggestions? Something not too expensive please. I can't just throw the coax out the window and it goes under the house for 3 feet and comes up in a bedroom/office.

05-06-2013, 08:54 AM
I live in the mountains of western Maine and I can tell you terrain has a LOT to do with reception. One of our repeaters is about 6 air miles from my house and I can barely get into it with a hand held yet another one is in NH 15 miles away and I have no problem with that one. I am often accused of being off freq into a distant UHF repeater because of the multipath from the mountains.

12-13-2015, 11:22 AM
Probably a terrain issue. Rotating the antenna will probably make no difference it is an omni. Your best bet is more height.

12-15-2015, 11:47 AM
A J Pole it is not (though I do admit it looks like one) J Poles do not need radials or Ground planes. Grounding the mount should, in theory, make no difference on that style of antenna.

12-15-2015, 06:47 PM
Can rotating the antenna improve signal?

Only if it's not pointing straight up (or straight down). If it is neither straight up nor straight down, then rotating it so it points straight up or down will improve the signal into other stations' vertically polarized antennas.

Not having it straight up or down will reduce the received signal strength (for each of you) by the square of the cosine of the angle by which it deviates from being parallel to the other guy's antenna. If the "other guy" is a repeater, his antenna almost always points straight up.

Ummm -- perhaps you meant rotating it about a vertical axis. No, that won't do squat.

12-15-2015, 09:44 PM
A J Pole it is not (though I do admit it looks like one) J Poles do not need radials or Ground planes. Grounding the mount should, in theory, make no difference on that style of antenna.

It certainly looks like a J-pole. Why do you say it isn't one?

The presence of 1/4-wave radials doesn't mean it isn't a J-pole. J-poles are almost never a perfect match to the feedline, and it is often useful to provide some sort of choke to prevent RF from flowing on the outside of the coax. Such a choke can be a coiled bit of the coax, or a ferrite toroid (which is what I use on my J-poles) or -- ta-da! -- quarter-wave radials.

It may not be a J-pole anyway, of course; just wondered why you seem so sure it isn't.

A closer photo would enable us to see how it's fed. Then we could tell for sure.

12-16-2015, 10:09 AM
Maybe the problem is the net controller guy! If you are using UHF it can be flaky I have a high gain VHF/UHF repeater antenna on my tower from one direction it is shaded about 50% by the house our VHF repeater and our UHF one are at the exact same location. On VHF I can hear HT's in Conway NH about 15 miles west. The UHF repeater I get about 1/2 scale the VHF full scale. If I walk outside on the other side of the house with an HT I can talk to the the UHF repeater with 5 watts and receive it full scale.

12-16-2015, 11:18 PM
... I was mounted on an inch and half pipe ...

Trying to visualize Doc mounted on a pipe. Doc, were you punished by impalement?

From The Devil's Dictionary, Ambrose Bierce, about year 1890:

Impale, v.t.
In popular usage to pierce with any weapon which remains fixed in the wound. This, however, is inaccurate; to impale is, properly, to put to death by thrusting an upright sharp stake into the body, the victim being left in a sitting position. This was a common mode of punishment among many of the nations of antiquity, and is still in high favor in China and other parts of Asia. Down to the beginning of the fifteenth century it was widely employed in "churching" heretics and schismatics. Wolecraft calls it the "stoole of repentynge," and among the common people it was jocularly known as "riding the one-legged horse." Ludwig Salzmann informs us that in Thibet impalement is considered the most appropriate punishment for crimes against religion; and although in China it is sometimes awarded for secular offences, it is most frequently adjudged in cases of sacrilege. To the person in actual experience of impalement it must be a matter of minor importance by what kind of civil or religious dissent he was made acquainted with its discomforts; but doubtless he would feel a certain satisfaction if able to contemplate himself in the character of a weather-cock on the spire of the True Church.

The historical Romanian statesman Vlad the Impaler was Bram Stoker's inspiration for his famous novel Dracula. In Romanian, the moniker Vlad the Impaler is Vlad Dracul.

But perhaps, instead, Doc meant something like this verse of The Erie Canal, a song I learned long ago, about age five, from a Burl Ives recording:

The cook she was a grand old gal,
She wore a ragged dress.
We h'isted her up on a pole
As a signal of distress.
Oh, the E-Ri-E was a-risin'.
And the gin was a-gettin' low,
And I scarcely think we'll get a drink
Till we get to Buffalo-o-o,
Till we get to Buffalo.