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Author Topic: Unique hidden HF mobile antennasanyone?  (Read 925 times)
N6HBJ
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« on: November 15, 2003, 12:37:45 PM »

Hello all, I'm thinking of going mobile in my truck but I don't want an unsightly HF antenna (40 and/or 80 meters) on my truck. Has anyone come up with any unique hidden antennas like maybe stringing a wire around the inside of the bed of their truck or any other ideas?

thanks

Mike.
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KE6PKJ
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« Reply #1 on: November 15, 2003, 01:02:02 PM »

Unsightly HF antenna!? There's no such thing! All antenna's are beautiful. But seriously, I have an old QST article that had construction plans for a concealed HF antenna in the fiberglass shell of your P.U. truck. I'll do a little digging and see if I can find it for you.
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K0BG
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« Reply #2 on: November 15, 2003, 07:40:06 PM »

Beauty is in the eye of the beholder, and you may think they're ugly, but I don't.

In any case, size is important. Short, small, and hidden are all prescriptions for added inefficiency in an area of amateur radio where inefficiency is a byword.

If you don't want to see it, then go VHF or UHF where the antennas as rather small in comparison.

Alan, KØBG
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N6HBJ
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« Reply #3 on: November 15, 2003, 09:20:21 PM »

Thanks Alan K0BG (for nothing). My question was about HF not VHF antennas. Why do even bother to answer my post if you have no valuable input?
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KA7RRA
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« Reply #4 on: November 16, 2003, 01:18:09 AM »

You could look at the little tarheal ant I installed one on my chevy surburban and I have talked to Japan and South America and to Winpeg Manitobia
DAve...
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K0BG
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« Reply #5 on: November 16, 2003, 10:54:12 AM »

Mike, I could have suggested you use a dummy load as it would be a little safer than running a wire inside your camper shell. You have to understand mobile antennas are a compromise at best, and "hiding" one just makes the losses greater.

In one of Don Johnson's books (available from Worldradio) he shows an installation where the coil assembly of a screwdriver antenna is mounted horizonally inside a fiberglass pickup shell with just the whip showing on the outside. No matter what sort of DC grounding you do with this type of setup, there is not a hint of a groundplane anywhere near the base of the antenna. Thus, the ground losses are so great it might as well be a dummy load.

A typical commercial 40 meter antenna has an efficiency of about 10%. Assuming you could properly load up a wire strung around the inside of a pickup shell, I suspect the efficiency would be on the order of 1% or less. Make contracts? Sure you can as any QRP operator can tell you. But if you want to have good results, you have to do better than just a simple chunk of hidden wire.

Alan, KØBG
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N6HBJ
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« Reply #6 on: November 17, 2003, 12:39:09 PM »

Alan,

I don't have a camper shell.

I'm well aware of a mobile antenna being a compromise (I've been a ham for 21 years).

I think the metal bed of my truck would make a good "ground plane."

The military have run horizontal whips on their vehicles which act like an "NVIS"(sic?)antenna successfully.

I'm thinking of a wire with a coil to physically shorten it and strung horizontally around all 4 sides of my pickup truck bed.

Anyway, back to my question. If there is anyone out there who has experience with this, please let me know.

Thanks all

Mike N6HBJ
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K0BG
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« Reply #7 on: November 17, 2003, 04:13:49 PM »

To answer your question directly, yes I have used loops on a vehicle. They work well if you can get the away from the body far enough. Although you could use a mobile loop on 15 meters, you can't get one far enough away from metal to be of much use. On 10 meters (perhaps 12 meters too) a loop can be used successfully, but I'm not sure if it would be as good as a standard whip.

On 6 meters a loop (squalo) works well and has both horizonal and vertical components due to its proximity to the body of the vehicle.

One thing to keep in mind as AA4PB always points out. Antenna performance is recipical. If it is lossy on transmit, the same can be said for receive. Amps and preamps help, but don't solve the basic loss problems.

It's sort of like race cars; there is no substitute for cubic inches. In mobile antennas, there is no substitute for length.

Alan, KØBG
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KS4XN
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« Reply #8 on: November 17, 2003, 11:00:58 PM »

Not exactly what you're talking about but there's a new breed of small screwdrivers by tarheel antennas and others that aren't the humongous type. They work with smaller coils by being installed higher up to lessen ground losses. Good Luck, I've been having a lot of mobile hf fun and just this weekend put in a Palm Paddle. Pray for me...Smiley

73 de John, ks4xn
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K5LXP
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« Reply #9 on: November 18, 2003, 11:31:27 AM »

Before you beat K0BG up too badly, he's pretty much right.  The short answer to your question is that if it could be done that way, it would be.  In racing, "there's no replacemment for displacement", antennas follow a similar rule.  Especially for 40 and 80M, to break 10% efficiency is quite a feat.  For a real treat do a search for stories about 160M mobile antennas, their main concern is keeping from hitting low bridges with their antennas.  Yes, you can come up with antennas that aren't too obtrusive but they aren't going to work too well either.  NVIS means just that- near vertical.  The 5% of the energy not lost to inefficiency that's radiated (QRP levels) will be going mostly straight up.  OK for working locals but you just might be able to beat that effective range with a good 2M FM setup.  A pickup bed can be a good counterpoise compared to a car, if you mount your antenna in the center of it.  An optimized Hustler mast/coil setup or decent screwdriver antenna mounted there will be a reasonable performer on 40-10, and as good as most on 80M.  It's about as much as you can ask for when your antenna is one tenth it's natural resonant length.

Mark K5LXP
Albuquerque, NM
k5lxp@arrl.net
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K8TDM
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« Reply #10 on: November 25, 2003, 01:13:51 PM »

I have a new 2004 1500 RAM pickup (and a Hemi)Smiley that I had the same concerns on.  I ended up with a High Serria Sidekick screwdriver mounted on the front of the bed near the rear window.  It is black and by tucking it up new the rear window frit it is fairly well blended in to the truck.  I also tried running 4 counterpoise wires around the bed which are concealed under the tarno cover side rails. I traped them between the rail strips and the bed.  Seems to work real well and pretty darn stealthy to boot.

-Tom
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N3ZKP
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« Reply #11 on: November 25, 2003, 06:46:22 PM »

Tom,

Radials should not be necessary if you have properly bonded the truck bed to the ground side of the antenna mount.

Just be aware that the closer you mount that antenna to the cab of the truck, the poorer the performance will be due to coupling between the cam and the antenna. Not a good thing.

You might try mounting it mid-ways back between the cab and the end of the box. I think you will find the performance improved, especially on 40m and 75/80m.

Lon

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N3ZKP
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« Reply #12 on: November 26, 2003, 12:42:01 AM »

Just an addendum ...

When it comes to mobile HF antennas, especially on 40m and 75/80m, you can have stealth or you can have performance.

It's darn near impossible to have BOTH at the same time. Smiley

Personally, my HS1800pro on my minivan is a thing of beauty!

Lon
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N8IWK
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« Reply #13 on: November 26, 2003, 12:21:04 PM »

How about a random length long wire?
Assuming you have a tuner to tune it, just drag the wire behind the vehicle, tie some tin cans to it and put a "Just Married" sign on the back of the vehicle. No one would ever suspect you are operating an HF mobile station.

PS: Just make sure the XYL or YL is in the vehicle with you, to make it look legit...Smiley
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N3ZKP
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Posts: 2008




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« Reply #14 on: November 26, 2003, 02:47:34 PM »

Too low to the ground to radiate well.

Now attached to a helium balloon ... <gg>
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