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Author Topic: mobile vhf antenna  (Read 1096 times)
AA4PB
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« on: July 01, 2003, 06:40:01 PM »

"works" is the key word here. Lots of things "work", some better than others. A rubber duck on an HT inside the car "works". So does a dummy load if you don't expect too much range. If you want it to work well then get out the drill and do a proper installation in the center of the roof. If you can't bring yourself to do that then you'll have to make some compromises and trade off "working well" for "ease of installation".
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KG4LJF
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« Reply #1 on: July 01, 2003, 07:05:34 PM »

Back in my early ham days, I had a old hy-gain 1/4 wave magnet mount antenna on the cab of my truck. Worked just fine for repeaters. Best I got was a machine that was about 40 miles away on 2 meters. wasn't a bad set up at all. Looked a lil' gawky, but who cares what it looks like, long as it talks good!
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AA4PB
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« Reply #2 on: July 01, 2003, 06:42:58 PM »

By the way, take a look at "Eek! Drilling holes! (follow-up)" a few posts down the list.
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KD4KNR
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« Reply #3 on: July 01, 2003, 05:00:02 PM »

I'm looking for a good 2 meter ant for my truck. I don't want to drill.
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WA4MJF
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« Reply #4 on: July 01, 2003, 05:28:21 PM »

Well, that is kinda mutually exclusive.

No good metal to metal contact and
all you have is compromise!

Once you realize this, I prefer a 1/4
wave whip, NMO mount, dead center of roof.

73 de Ronnie
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W4TYU
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Posts: 518




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« Reply #5 on: July 01, 2003, 05:57:53 PM »

An old timers theory is that any antenna that works is a good antenna.

That said. A magnetic mount whip in the center of the roof of the cab.
OR
a droopy ground plane mounted on a short mast on the rear bumper.
OR

A whip on a mirror mount (if you have the large mirrors)

Ole man JEAN
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K6ZZZ
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« Reply #6 on: July 01, 2003, 10:49:20 PM »

I bought a truck, last Saturday, that I mounted a 2m radio in...I have used mag-mounts for 7 or 8 years and this time I want to "plant" an antenna...right thru the roof of this truck, but discreetly hide the coax...you know, I want to DO IT RIGHT!!! I am wanting a tilt over type...and a VHF only antenna. Does anyone have any suggestions on brands/models that are relatively inexpensive ($50-$60 or so for EVERYTHING)? Or am I going to have to fork out the cash?

John / K6ZZZ
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N6AJR
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« Reply #7 on: July 02, 2003, 12:18:07 AM »

drill the hole in the back drivers side rail and run the coax behind the tailite.  works good and a pl-259 to 3/8 X 24 mount is $5 ..

other than that, they make a rubber plug that fits in the stake holes in the bed and you tighten up the bolt and it squeezes out and holds tight and has a plate on which you mount the antenna.. no holes.
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KD7EVS
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« Reply #8 on: July 02, 2003, 12:33:11 AM »

don't spend 40$ for a stake mount. go to walmart get a stake hole ancor ($2.50) go to home depot get a sturdy 2inch wide piece of metal about 4 inches long. drill two holes in it. one of which 1/2 inch  (to which you add a $4 pl259 to 3/8x24tpi mount)  then take the ancor apart add one washer to the anchor bolt put the piece of metal on, add the other washer, put the anchor back togehter. put it in the stake hole. tighten it (no holes). attatch the antenna and a short ground strap.

I spend a total of 7 dollars on my stake hole mount. don't pay 40$ plus shipping when less than ten bucks and a half hour you can custom build one.

73
zeb
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W9WHE
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Posts: 254




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« Reply #9 on: July 02, 2003, 10:21:51 AM »

Ignore those that say you MUST drill. They likely own junk so they don't care!

Find a "lip" on the hood, hatch or other place and use a lip mount from diamond. Buy any of their 1/2 or 5/8 wave antennas. Look in the AES catalog, they carry bed-rail mounts and bed-hole mounts. ALL will work well.
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K5LXP
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« Reply #10 on: July 02, 2003, 11:35:19 AM »

W9WHE wrote:

> Ignore those that say you MUST drill. They likely
> own junk so they don't care!

Go to http://www.qsl.net/k5lxp/mobile/mobilemain.html and look and the junk I've drilled holes in.

I've drilled more holes in more cars, trucks and heavy equipment than most hams will in a lifetime.  From a performance point of view there's no other option.  Other posters have pointed out that "everything works", but correctly observe that temporary mounts provide compromised performance, or even damage to the vehicle.  Reading Alan KØBG's articles here on eHam on antenna mounting can be enlightening, seems hole drilling is second only to the no-code debate.

If you get performance acceptable to you with a temporary mount, and are willing to accept the potential damage they can inflict, that's fine.  More often than not however, most hams eventually "upgrade" to a through-hole antenna mount because it looks and works better than temporary mounts.

Mark K5LXP
Albuquerque, NM
k5lxp@arrl.net

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W0FM
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« Reply #11 on: July 02, 2003, 01:21:11 PM »

For W9WHE.....

A copy of an excerpt from my post to an eHam Article a few weeks back on drilling holes.  Some pretty nice junk!:

"When I worked for Motorola's Cellular Group in 1984, we installed thousands of cell phones (trunked mounted transceivers with front mounted control heads) in luxury cars of all types (and prices) including August Busch's (the beer guy) Porsche, a hotel developer's Rolls Royce Silver Cloud and Barbara Streisand's Bentley. EVERY VEHICLE got a hole drilled in the center of the roof or center of the trunk lid for the antenna. If you didn't want the hole, you didn't get the cell phone. Right or wrong, that was the stance that Motorola took and it was strictly to optimize the transceiver's performance."

It's not just junkers that get holes drilled.

73,

Terry, WØFM
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W9WHE
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Posts: 254




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« Reply #12 on: July 02, 2003, 04:58:28 PM »

HOW ABOUT SOME FACTS. A Single "S" unit difference in signal requires a 6 Db change, or a QUADRUPLING of your power (i.e. from 50 to 200 watts). Two "S" units would require going from 50 to 800 watts. Do you think drilling a hole will be equal to quadrupling your power?  Moreover, even if it were true, is a single "S" unit worth drilling a hole? You decide.

Ask those "drill a hole" guys to show you ACTUAL scientific test data (not unscientific - anectdotal nonsence) demonstrating a 6 Db (or greater) difference at VHF between lip and hole mounting the same antenna. It doesn't exist!

Anyone that says you "must" drill a hole to get excellent VHF performance is wrong. A 1/2 or 5/8 wave on a lip mount will give excellent performance (ask any of 50,000 hams) ESPECIALLY, if elevated above ground on a truck! The set screws on a lip mount (4 on the larger lip mounts) will make good electrical contact to the metal body for the counterpoise.

Before you drill ANY holes, go with a lip, luggage rack, bed rail, bed hole, or even a magnetic mount. If you do, you will not see a need to drill any holes.

Drilling holes is VASTLY over-rated.



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W9WHE
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Posts: 254




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« Reply #13 on: July 02, 2003, 05:28:50 PM »

K5LXP writes:

"Reading Alan KØBG's articles here on eHam on antenna mounting can be enlightening, seems hole drilling is second only to the no-code debate".

Actually, its NOT.

K0BG writes about HF (that's 1.8-30 Mhz) where ground is FAR more difficult and FAR more important than at VHF.

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WB2WIK
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« Reply #14 on: July 02, 2003, 06:15:18 PM »

W9WHE, what axe have you to grind in the "drilling hole" debate?  I don't get it.

I guess when I punched a hole in the roof of my new Jaguar XJ6, purchased new in 1984, it was a junker.  Same probably went for my 1997 Lexus LS400 -- another junker.  

As for scientific evidence, I wrote a fairly comprehensive article for the "VHF" column in CQ magazine in 1985 on this subject, using a beachfront location at the Jersey shore (flat as a pancake, virtually reflection-free) as a test range and quantifying data to within about +/- 0.2 dB; there was *far* greater than 6dB difference not only between antenna vehicular mounting locations, but also between various antenna models at identical mounting locations.

The Larsen Kulrod NMO-150 5/8-wave whip mounted in the center of the vehicle roof (a Volvo station wagon) blew away everything else, with regard to both model and location.

I did not try to qualify the reason for this, just provided a great deal of actual test data.  Data was accumulated using tunable, calibrated, sensitive FS meter (actual 2m FM receiver with limiter voltage output lab calibrated in 0.2 dB increments over a 20 dB range, and switchable, calibrated attenuator in antenna line), using multiple signal sources while driving the vehicle in a fixed circular pattern 100' in diameter (15 wavelengths) over a flat surface adjacent to the Atlantic Ocean, and repeating the same series of tests using multiple antennas and mounting locations.  Helper KT2B was on hand to assist and verify data.

Anyone who thinks there's not 6 dB difference between mounting locations for a 2m mobile whip hasn't tried this test.

(BTW, the Larsen Kulrod "mag mount" base was also the very best tested at the time, and outperformed everything from Antenna Specialists, Hy-Gain, Cushcraft, et al, for some reason.  While still being 3-4 dB down from the thru-hole NMO base at the same location on the vehicle, the Larsen rectangular-shaped magnetic base was simply more efficient at 146 MHz.  Never determined why.)

WB2WIK/6
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