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6m antenna options

This forum is dedicated to helping people with questions about installing radio equipment in vehicles. This can include antenna installs, electrical wiring questions/problems, and mounting systems. Pictures of installs are welcome.

Note: Discussions regarding lighting, sirens, and other equipment now has its own forum in the 'off-topic' section below.

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K4RXR
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6m antenna options

Postby K4RXR » Tue Nov 21, 2006 2:05 pm

[Potentially Off-topic]

I'm considering various antenna options for 6m FM and I'd like the group's opinions. The vehicle in quesiton is a Ford Expedition so it has lots of roof surface and I'm not concerned about drilling holes.

Here's what I see as possibilities:

1. A full-size quarter-wave on a ball mount on a rear fender. The problem I see with this is that roughly half of the antenna will be below the roof line alongside the rear cargo area. Will the presence of the roof and the D-pillar appreciably degrade the antenna's performance? Another issue is that the fuel filler is on the left side so that might steer me towards putting the ball mount on the right side, but the AM-FM broadcast antenna is imbedded in the right rear side window which might cause even more headaches.

2. Use a base-loaded quarter-wave, ala Larsen NMO50, mounted on the roof. The base load will reduce the antenna's efficiency a bit, but the antenna would have virtually no obstructions. The antenna would, of course, be an obstruction because of its height, but I already have a 5/8-wave for VHF up there.

3. Some sort of multi-band antenna along the lines of a Diamond CR627. That thing is 5 feet tall and it has some stiffness (unlike the flexible Larsen whips), so it would definitely pose some mounting problems. I suppose I could fabricate a bracket to mount it somewhere above the rear taillight.

4. What else?

Thanks for your thoughts.

Bob...

fineshot1
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Postby fineshot1 » Tue Nov 21, 2006 3:38 pm

I picked up a used Comet SB14 & triplexer and it works great on 6 & 440. I dont use 2 mtrs enough to evaluate it there. Gain = 2/6/440 - unity/3.5/6dBi and power rating is 120Watts. Length = 1.08meters. I have compared it on 6 meters to the Larsen 6 meter nmo mount and its about equal to it. Thats not bad for a multiband antenna.
fineshot1
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jhooten
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Postby jhooten » Tue Nov 21, 2006 4:34 pm

An NMO150 cut to 2 meters is 49 inches long. An NMOQ52 cut to 6 meters is 52 inches. I have one of each on the roof of my 1 ton and have no problems.

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kb0nly
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Postby kb0nly » Wed Nov 22, 2006 5:22 am

I have an SB15 triband antenna on my mobile, works great! Just use a diplexer or triplexer, to combine all the radios to one antenna.

I was running three X9000's through a triplexer to this antenna before i switched to my FT-8900.
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Max-trac
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Postby Max-trac » Wed Nov 22, 2006 7:19 am

NMO in the middle of the roof!
There are many antennas that are good, Maxrad, Larsen and the Motorola Spectrum....

You can experiment with multiband that way also, if you like.
We have had good luck with the Maldol that covers 6m Ham.

With your setup, the ballmount would have unpredictable results. Any metal within a wavelength or so can screw things up.
The WORST thing is a HF multiband that also covers 6.

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Postby gws » Wed Nov 22, 2006 7:32 am

If your just trying to work local repeaters and locals simplex location is of minimal issue. most police depth side mount there VHF low and live with the directionality it gives

Who you trying to work?
Gary N8EMR

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kb0nly
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Postby kb0nly » Wed Nov 22, 2006 7:50 am

Max-trac wrote:NMO in the middle of the roof!
There are many antennas that are good, Maxrad, Larsen and the Motorola Spectrum....

You can experiment with multiband that way also, if you like.
We have had good luck with the Maldol that covers 6m Ham.

With your setup, the ballmount would have unpredictable results. Any metal within a wavelength or so can screw things up.
The WORST thing is a HF multiband that also covers 6.


The HF multiband antennas on 6m are ok as long as your goal is SSB use. Almost all of them will only cover the lower end of the band. But since you most likely want FM use then yes, they do suck there.

I used to have a Huster MO-3 mast, which is 54", on a ball mount on my old van, that's an effective 1/4 wave on 6. I added a 10m resonator to the top and after a bit of tweaking i was able to get the antenna effective across the entire range of the lowband X9000 that i was using. Not perfect mind you, but good enough for local work.
Duct tape is like the force, it has a dark side and a light side and it holds the universe together.



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Pj
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Postby Pj » Wed Nov 22, 2006 9:27 pm

My last two mounts were "L" brackets on the front fender/hood. Comtelco cut to 52 and works really well from 42-54 (X9000 and Orion).

Previously was on top of a S10 Blazer (NMO in the rear) and worked really well there too (all at 100watts).

I guess I have been lucky.
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Birken Vogt
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Postby Birken Vogt » Thu Nov 23, 2006 12:00 pm

I use a NMO Antenex C47 on 52 MC with two turns of coil removed to bring the freq up a little bit. A friend just removes all the coils and puts the wire straight from the contact to the whip and uses a full quarter wave whip on the C47 base, however he has a smaller car. As far as performance goes a full quarter on top is best obviously, a quarter on a ball mount is almost as good (though large and ugly) and then a base loaded shorter antenna is a compromise (though not bad). I use a base load because it's a full size truck and I am afraid I would wipe it off in the woods somewhere though.

Birken

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007
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Postby 007 » Fri Nov 24, 2006 2:41 pm

I'll fly the ball mount flag :D Long live the lowband ball mount.

That said, a ball mount whip cut for 52 MHz is only something like 5" taller than a base loaded NMO50B, so you really don't gain much other than 4 big holes in the fender.

Go with a base loaded 1/4w NMO antenna on the roof.
Do not make Sig angry...he'll just keep ringing the bell.

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apco25
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Postby apco25 » Sun Nov 26, 2006 6:45 pm

Unless you're like my ride and the whip ends up being about 9 feet to the tip when on the roof....

Ball mounts just look wrong mounted on the right side rear fender.

Even worse is the front brush guard mount the aussies use all the time.

Jim,

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"Some men just don't know their limitations"
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K4RXR
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Postby K4RXR » Tue Nov 28, 2006 9:28 am

Thanks for the replies and suggestions. I'm going to go with a Larsen NMO50 or something similar mounted at pretty much the center of the roof in both directions. The hole was drilled, the mount installed, and the feedline routed last weekend. Maybe this weekend, I'll get the antenna mounted and tuned. This has been an on-going project for about 16 months, so I'm in no hurry.

Bob...

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motorola_otaku
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Postby motorola_otaku » Tue Nov 28, 2006 9:52 am

The 6m FM guys around here use these. They have one for 50-54, but Tessco isn't turning it up in a search. I have personally seen that antenna and a 110w Maratrac work Mexico City from southeast Texas on 52.525.

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apco25
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Postby apco25 » Tue Nov 28, 2006 10:17 am

They do have them. I have one of each for 29-33 and 50-54. Due to the coil size the 50-54 is actually taller than the 29-33 cut.
"Some men just don't know their limitations"

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mike m
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Postby mike m » Wed Nov 29, 2006 9:36 am

Just get a suitable diplexer and use your 2 meter 5/8 wave antenna as a dual bander.

It will work as a 1/4 wave on 6 FM and as it's intended design on 2 meters.

Mike

WB5ITT
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Postby WB5ITT » Sat Feb 10, 2007 8:08 am

K4RXR wrote:Thanks for the replies and suggestions. I'm going to go with a Larsen NMO50 or something similar mounted at pretty much the center of the roof in both directions. The hole was drilled, the mount installed, and the feedline routed last weekend. Maybe this weekend, I'll get the antenna mounted and tuned. This has been an on-going project for about 16 months, so I'm in no hurry.

Bob...


Put a NMO150 there instead....you can use it on both 6 and 2 and it radiates better than the NMO50...been there, did it 30 years ago...still running NMO150s on 6 ;)
Chris
WB5ITT

Jim202
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Postby Jim202 » Sun Feb 11, 2007 12:20 pm

If you only want to use this antenna for 6 meters, then go with
the Larson NMO-Q base. Put a W540 on top of the base. They
work just fine. Never had to do any tuning on the FM portion
of the band when using this combination and 100 watt
transmitters.

This uses the standard NMO mount. If by some chance you hit
a low tree limb, the Larson base will crack and save the roof.

If you use that big coil from Tessco, I think that uses the ASP
mount that has the large teeth that are on the underside of the
roof. If that coil takes a hit, it tears up the roof in a big way.

Used the Larson base coils on large trucks and cement
mixers. They never had to repair another roof after switching
to the Larson bases. The coils were by far cheaper to replace
than the body work on the roof from an ASP type mount.

Jim


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