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Author Topic: HF ant on mobile home roof -- how low can it be?  (Read 1487 times)
K1LDS
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« on: October 16, 2007, 09:45:43 PM »

I am in a real challenging situation.  The park manager is looking for any excuse to annoy residents not on his Buddy List.  He and the guy who works for him routinely troop through everyone's yard to read water meters and make sure that nobody has stuff outside (even in the back).  Worse, the lackey is a former employee of mine and lives across the street, so he has a constant view of my place.

To give you an idea about this guy, I have a service dog and he has been trying to run us out of the park because she doesn't fit the "park standards" for pets (service animals are exempt, he knows it, but still . . .).  This added attention compounds the problem of running HF.

Things like flagpoles won't work.  I wish that I could find one of the later AEA Isoloops, I could convince them that it's an outdoor UHF TV antenna.

I have some ideas:

1)  put a wire above the aluminum roof where it can't be seen from the ground.  How low can I mount, say, a 20M dipole?

2)  I have an 8 x 12 wooden shed that I could hide a loop in the roof of, but what kind of performance would I see?

3)  Shoot a dart into a nearby utility pole and run a single small-diameter wire to it from a corner of the mobile.

4)  Run a wire to a corner of the carport from the top of the air conditioner (about 40 ft), but again, there is the proximity of the metal carport roof to consider.

The really annoying part of this is that I have another place where I can run anything I like, including a Beverage, but my work has me based here for at least the next couple of years.

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ONAIR
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« Reply #1 on: October 16, 2007, 11:25:03 PM »

    I think they have to allow you to put up a TV antenna or a satellite dish.  The mast or cable running from that "antenna" can be your ham antenna!
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K1LDS
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« Reply #2 on: October 17, 2007, 04:01:55 PM »

The question is how high it has to be off the metal roof to work well?

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K5LXP
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« Reply #3 on: October 18, 2007, 06:26:06 AM »

It would be measured in feet, not inches so it probably wouldn't be as stealthy as you're looking for.

In addition to the sat dish or TV antenna with adequate "guying", what about something like a "bird feeder" on a tall pole?  Since you mentioned 20M, a quarter wave vertical for that band is only 16ft.  Counterpoise wires in the lawn are invisible.  A little bird feeder at the top completes the picture.

I think anything you put on your roof would be hard to disguise, but a stealth wire or vertical elsewhere might blend in better.  Any trees around?  How about a buried feedline to the utility pole you mentioned, with a thin wire running up it's length?

Mark K5LXP
Albuquerque, NM
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K1LDS
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« Reply #4 on: October 18, 2007, 07:19:21 AM »

No poles of any kind.  There is a tree on the lot, but once the leaves leave, a wire would be spotted.

I'm thinking that I cat run a wire from a top corner of the air conditioner (about 4 feet above the roof) to a mini sat dish on a corner (about 2 - 3 above the roof) or to my wooden shed roof.  That's why I need to know how close to the roof the wire can be and still work.

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KG4RUL
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« Reply #5 on: October 18, 2007, 10:16:49 AM »

Check out the FCC rulings - 12' above the structure is the maximum for an OTARD antenna.  By the way, OTARD stands for Over The Air RECEPTION Device, reception being the keyword here.
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N3OX
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« Reply #6 on: October 18, 2007, 03:37:23 PM »

", but once the leaves leave, a wire would be spotted. "

Not if it is insulated with dark colored wire and runs straight up the trunk on the side away from his house...

A PAR End-Fedz might be a good solution... I think they have one that does 40, 20, 10.

Or you could do a homebrew version of the same thing.  

All end fed antennas need an RF ground, but one fed at a high voltage point like that doesn't need much and generally works efficiently with just the coax shield as a single "radial"

If they're looking hard for it, they'll find it, but if you can install it stealthily they'll never notice it's there, or at least not for a really long time.

Dan

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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
K1LDS
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« Reply #7 on: October 18, 2007, 06:15:07 PM »

I say again, they go through everybody's yard, and they are looking for a reason to annoy.  I may give the tree vertical a try, but I'm hoping for a better solution.  The tree belongs to the park (though, somehow, all the leaves that fall of it are mine . . .).

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N3OX
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« Reply #8 on: October 18, 2007, 08:24:15 PM »

Is money a particular concern?  I think your instinct with the Isoloop is good...

You could build a magnetic loop that would handle a few hundred watts and do as well or better than the AEA Isoloop, and I think it would work pretty well even inside a wooden shed :

http://n3ox.net/projects/magloop/magloop1_lg.jpg

The nice thing about magloops is they do work close to the ground and they're small.  I built mine for fun because I was extremely lucky to retrieve the vacuum variable capacitor from a junked piece of equipment, and I can say with absolute certainty that if I had to stick to a 4 foot antenna, this would be the one.

The disadvantage is that it's got a $150 capacitor and probably $50+ of copper tubing in it, add on another $50 for motor, shaft accessories, hardware... starts to add up, and you haven't even added in your time to fabricate.

Without the motor, I'd go crazy trying to use one.  This one has to be retuned every 3-4kHz on 40m, maybe every 10kHz on 20m... but that makes it a more time consuming homebrew project.

But, an order to Max Gain Systems for the capacitor, a trip to a plumbing store for some copper, and you have a real working antenna in the shed.

You could even make it bigger and sacrifice the higher bands (15, probably 17) to gain 80m.

Dan







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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
K1LDS
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Posts: 20




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« Reply #9 on: October 19, 2007, 08:04:04 AM »

Money IS an object, but the problem with the Isoloop is FINDING ONE!

MFJ has a loop also (or they had one, it's on their site but not in the HRO book).

Building a mag loop isn't an option -- if it looks storebought, they will assume it's just a TV antenna, but one that I build would be questioned.  I have gone a long way here to NOT let them know I'm a ham (the antennas on my car are explained away as being there because I do disaster response).

I'm even thinking of running out to Pacificon (1500 mile round trip) in hopes that the ham swap will provide a solution (okay, okay, Pacificon wouldn't be the ONLY reason for going to California, but you get the idea).  I've never been there, though, and the last ham swap I hit was disappointingly small, so I dunno . . .



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W3LK
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« Reply #10 on: October 19, 2007, 09:45:25 AM »

<< (the antennas on my car are explained away as being there because I do disaster response). >.

Why is it any of these people's business what you have in and on your car?

73,

Lon - W3LK
Naugatuck, Connecticut
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A smoking section in a restaurant makes as much sense as a peeing section in a swimming pool.
N3OX
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« Reply #11 on: October 19, 2007, 12:36:37 PM »

Keith, I think you should put something in the shed.

If it's just a plain wooden + shingled shed it won't hinder RF much.

It gets you off the hook for storebought antennas... but I think a magloop could still be the best solution for an in-shed antenna.

8x12 isn't big enough for dipoles or "large" loop antennas to work particularly well, but a 6' diameter magloop hung vertically from the roof peak could really get out.

A quality shortened dipole could work too but any efficient short/small antenna is going to be narrow band and it's hard to motorize the dipole.  

If these guys are really trying to dig deep to find the  hidden radio transmitters in your development there, they might just look at your "UHF antenna" with binoculars and google "Isoloop" and then you're sunk.

Dan

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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
K1LDS
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Posts: 20




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« Reply #12 on: October 19, 2007, 03:54:17 PM »

It's not that they had any problem with the car, but by explaining the antennas away, I've kept people from knowing that I'm a ham.  This means that I'm not the first one they blame for TVI, flickering lights or the Heartbreak of Psoriasis.

That also means that if I put up an antenna that looks like it might be for TV, they will assume that it IS for TV.
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K1LDS
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« Reply #13 on: October 19, 2007, 04:33:31 PM »

" . . .a 6' diameter magloop hung vertically from the roof peak could really get out."

Assuming that there were room for a 6' vertical Hula Hoop (there isn't), I think that it would be masked by the adjacent mobile homes.  Perhaps horizontally-mounted would work better, and I've got room for that.

"If these guys are really trying to dig deep to find the hidden radio transmitters in your development there, they might just look at your "UHF antenna" with binoculars and google "Isoloop" and then you're sunk."

If it's painted on, I can paint it out.  If it's in raised letters, I can flip it over or tape over them.  That's just cosmetics.    

Not trying to argue, just fine-tuning the situation.

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N3OX
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« Reply #14 on: October 19, 2007, 05:32:18 PM »

"Not trying to argue, just fine-tuning the situation."

Understood... well, you know your enemy better than anyone else ;-)

So if you can find your Isoloop or MFJ version and can convince these guys that it's a TV antenna, I expect you'll be happy.

A good magloop is a pretty good antenna.

Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
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