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1-10 of 16 messages
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Rooftop install for screwdriver antenna
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by KC7MYN on September 10, 2009
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I have antenna restrictions and would like to install a screwdriver antenna on my roof out of sight of the neighbors. Any ideas??? I saw an article once about using an old music stand and setting up radials off the stand. How many radials and how long? Another ideas welcome...Thanks...
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RE: Rooftop install for screwdriver antenna
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by KJ6AMF on September 10, 2009
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I'd try a wire antenna first, like a random wire, inverted L, or a loop. It would be a lot cheaper, easier to hide, and probably a better performer. Plus with a screw driver, you'd have to have someway to tune it for each band, either by going up the roof every time you need to tune it, or having one of the more expensive motorized screw drivers.
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RE: Rooftop install for screwdriver antenna
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by N5LRZ on September 10, 2009
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Well first off do not put it on the roof.
Make a suitable stand and put it in your back yard so that you can take it inside when you are finished. with 3 or 4 quarter wave counterpoises.
Warning, contractual agreements do not have tap backs. Consult you legal rep and have him read and consult with you on the terms of your contract in re to external antennas. Have him or her consult with you as to possible financial penalties and legal actions that the HOA and or landlord can use against you in a court of law, the least of which is a court order from the judge directing you to remove your external antenna with possible contractual manditory fines against you for breech of contract.
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RE: Rooftop install for screwdriver antenna
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by AA4PB on September 10, 2009
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For a rooftop install you will need a set (3 or 4) of 1/4 wave long radials for each band you want to operate. If your back yard is surrounded by the normal houses, sheds, trees, etc. then you'll likely find the performance a lot better on the roof provided you have the proper radial system.
For LRZ: Normally you wind up in court only after you refuse to abide by the HOA's formal request to take the antenna down.
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RE: Rooftop install for screwdriver antenna
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by N5LRZ on September 11, 2009
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Re PB....
Sooner or later some neighbor is going to bitch and file a complaint to the HOA and all hell will break loose upoon this guy. It may not be tormorrow, next week or perhaps next month or year BUT it will happen eventually.
Neighbors have a way of getting very bitchey now and then seeking justice aka revenge. And in a HOA they have contractual law and probably very severe financial penalty on their side as big sticks to 'Force' compliance.
NOT living in a HOA on the other hand the amateur op can tell the neighbor to go get screwed.
'SOMEONE' should have told this guy BEFORE he even took his test that he was going to face antenna explaining that CONTRACTUAL LAW has no tap back and hell when he got his license when it came to antennas. PERHAPS he would have thought twice about wanting one in the first place and wisely said screw amateir radio, Golf sounds better.
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RE: Rooftop install for screwdriver antenna
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by N5LRZ on September 11, 2009
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If you are asking the question in theory, the sheets of metal would have to be bonded into one large sheet of metal. Merely touching is not nearly enough. Dirt and grime would get inbetween the sheets and break any contact between the sheets over time.
Natural corrosion over the years would not only separate the sheets but also act like a dilectric causing problems as well
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RE: Rooftop install for screwdriver antenna
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by K5LXP on September 13, 2009
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N5LRZ wrote:
> put it in your back yard ... with 3 or 4 quarter wave counterpoises.
1. 4 radials for a ground mounted vertical are woefully inefficient, especially when you're starting with an already marginal antenna.
2. Radials are not resonant on the ground.
I can't believe you would recommend a solution that is not optimum.
Besides, you're leaping to the conclusion that any antenna at his residence is banned. His covenant may just preclude ones visible from the street, or above a certain height.
A roof or ground mounted screwdriver is a solution but it wouldn't be the first one I would pick. Some kind of wire antenna, even just random length fed against a counterpoise or a simple balanced fed doublet can be very efficient, effective and stealth.
Mark K5LXP
Albuquerque, NM
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RE: Rooftop install for screwdriver antenna
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by N5LRZ on September 13, 2009
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LXP...
IF you had bothered to read the test results of various independant tests conducted over the years using computer generated results you will see that quarter wave lengths on the ground are NOT intendended to be resonant. They are meant to copper plate, so to speak the earth surround the antenna. The MINIMUM effective utility lingth length for any kind of very siginficant ground losse reduction starts at a quarter wave with the longer the length of wire and the greater the number of radials the LESS the ground losses, the LOWER the angle of radiation for any ground mounted vertical AND a LOWER input impedance for the antenna. OPTIMUM length of ground radials is about a full half wave length each leg of the ground radials.
16 radials are OK. About 32 are better. 64 radials even better yet. The greater the number of full length radials the better the ground field that the vertical antenna will have to work against.
The SOLE and ONLY goal of ground radials is to effectively "Copper Plate" an area of the earth ideally 1/4 to 1/2 full wave length in all directions from the base of the antenna.
And IF possible, which unfortunately it is not, we would physically remove an entire layer of earth in a full 1/2 wave length surrounding a small dirt patch and dip it in pure copper after which it would be returned to its former position.
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RE: Rooftop install for screwdriver antenna
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by K5LXP on September 16, 2009
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> IF you had bothered to read
I can't read, I just look at the pictures.
> The MINIMUM effective utility lingth length for any
> kind of very siginficant ground losse reduction
> starts at a quarter wave
This is wrong.
With few radials (the cited quantity 4) there is little benefit beyond .1wl. You need to approach quantities of 100 radials before the quarter wave length begins to provide a benefit. The upshot is the ground losses would be so high it would be easy to attain a match to 50 ohm line.
The reason I brought up resonant is that would be the only way 4 radials would have any chance as an efficient counterpoise, as part of an elevated groundplane configuration.
> 16 radials are OK. About 32 are better. 64 radials
> even better yet.
We cam agree on that.
Seems like a lot of trouble to go through for a compromise vertical though. So for the original poster I would focus on suspended wire.
Mark K5LXP
Albuquerque, NM
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