Antenna Placement - Spacing.... how much for what bands...

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alex
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Antenna Placement - Spacing.... how much for what bands...

Post by alex »

Alrighty -

Monday the truck is getting some holes drilled in the roof, and it's finally getting it's permanent whiskers...

I have:

VHF (110w Astro Spectra)
UHF (25w MCS2000 - though might eventually get upgraded for more power)
800 (MCS2000 35w)
V/U Dual band antenna (essentailly a 4th spot for future expansion, scanner, other projects)

I'm wondering what would be ultimate spacing plan?

Make a square out of the antenna's? Straight Line? maybe the 800/uhf in a row and dualband + VHF at the same level?

Being installed on a 4 door explorer...

IIRC - you want around 19" for VHF - but what can you get away with interms of spacing and still have it all work in harmony...

Ideas/Suggestions?

I'm not personally doing the drilling - I'm leaving that to the guy with insurance :)

-Alex
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007
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Post by 007 »

Since this is on a 4 door Explorer, space them either in a row dow the center with 20-22" in between, or put them in a rectangle on the rear 2/3 of the roof, with 20-22" in between them from left to right, and 20-22" of space front to back on each side.

It works good and looks good, especially with 1/4w antennas.

Look at Apco25's install pics...I just saw this in person yesterday, and looks great. If he didn't have the callsign plates, it'd be a total fed install.
Do not make Sig angry...he'll just keep ringing the bell.
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jim
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Post by jim »

I space them evenly. I have never once experienced and interference/intermod. I always try to do them in a straigh row, since I think that side-by-side or square patterns look like crapola.
Sometimes you'll have to give or take several inches if there's a crossmember in the roof.

If you have two of the same band, just keep them physically far apart.
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Pj
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Post by Pj »

My old S10 Blazer had UHF, VHF, Lowband x9000 100 watt suckers all with roof mount antenna's. I want to say they were spaced about 18" from each other. If I can find a ruler, I will go outside and measure since my brother owns the truck now.

Never had any cross-band interfearance.
Lowband radio. The original and non-complicated wide area interoperable communications system
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apco25
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Post by apco25 »

When I had the Yukon I had all the antennas in the center as a single row.

The Suburban antennas are spaced 22 inches apart in a square pattern in the rear 2/3 thirds of the roof. Part of the choice to do it this way was due to the headliner being split into two pieces. I also ended up with m ore room to space out same band antennas or add more in the future.

Besides it looks better this way and less like a mohawk from the 80's!

If you do it all in a row and you end up with say two antenna same band try to space them at oposite ends of the row. Only problem is this tends to goof up an spatial considerations that were made in planning what antennas goes where.

We tend to line up objects in ascending height when it comes to antennas.
"Some men just don't know their limitations"
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wa2zdy
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Post by wa2zdy »

The standard rule is they should be at least a quarter wave apart. That of course means the greatest spacing should be around the lowest frequency antenna. A high band and a UHF antenna should be 19 inches apart - the quarter wave at high band.

As for the layout - whatever looks pretty to you. Just the keep the spacing in mind.

I had my Syntor X on 2m putting out 135 watts and my GM300 on 440 with the antennas on the trunk lid about 2 feet apart. There was absolutely no interaction at at all. I did extensive testing and there was zero desense to either caused by the other.

I'd be careful about having a scanner mixed in there though. That broadband front end is likely to get fried by RF from close by.
Chris,
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Wesley Chapel, Pasco County, Florida
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commtek
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Post by commtek »

I agree with Jim. Space them evenly as you can in straight line 12 inches or more apart. Never seen a problem with this method, assuming the antennas are grounded and tuned appropriately.
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apco25
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Post by apco25 »

Ideally the rule is space them 1/4 wave apart at your lowest operating frequency.

using the square pattern you can place UHF and 800/900 bands closes to the outside edges since they need a smaller ground plane.
"Some men just don't know their limitations"
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central150
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Post by central150 »

On my Sportage', I have them in a row, about 10 inches apart, starting with the 800, then uhf, then vhf. Works well for me..

-Tony
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alex
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Post by alex »

Here's what I ended up doing on the truck:

UHF Comtelco Antenna
Image

VHF and Dual Band Antenna (VHF has the large coil at the bottom of it.)
Image

(from Back to front):

DUAL BAND -------------------VHF

-------------------800

-------------------UHF

(dash's are just stupid place holders since it won't insert spaces where I want them :))

Image


Part No's:

VHF - A1511A
UHF - A1842
800 - A1183B
DB - 1131B


Sorry for the poor Image Quality, but whatcha goon do with a crappy camera at 12:30am after finishing the install...

:)

The Antenna's came from:

Electrocomm West
Larry Feiggee
1-800-262-3478

Mention Stan (USPSS)'s name to Larry, and he'll take good care of you.

Thanks to both Stan and Larry (and the guy with insurance who did the drilling for me...).

-Alex
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WK9F
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Re: Antenna Placement - Spacing.... how much for what bands.

Post by WK9F »

alex wrote:I'm not personally doing the drilling - I'm leaving that to the guy with insurance :)

-Alex
Chicken! :wink:

You're not a radio nut until you've drilled a few holes in a new vehicle.

Jerry
I am a bomb technician......If you see me running, try to keep up.

This space for rent....E-mail for details
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Tom in D.C.
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Drilling holes in vehicles...

Post by Tom in D.C. »

Non-pros, like me, should limit their drilling to trunks and hoods, drill a 3/8" pilot hole, then finish with a Greenlee 3/4" punch.

People who do it for a living can take down the headliners and then drill the roofs, as far as I'm concerned.

I can patch/make do with anything EXCEPT a ripped headliner.
Tom in D.C.
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WK9F
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Post by WK9F »

I hear 'ya.

I have the special 3/4" hole saw with the depth stop on it. All I do is loosen the headliner near the edge then shove a 1x4 in between it and the roof, just to make sure the pilot bit doesn't accidently contact the liner. The depth stop will contact the roof before the saw can push it's way through to the liner.

BTW - Alex, The install looks great.

Jerry
I am a bomb technician......If you see me running, try to keep up.

This space for rent....E-mail for details
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USPSS
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Post by USPSS »

Don't anyone feel stupid, I was at a shop in Northern VA a few weeks ago and a new tech was installimg a GOVT. truck, he was drilling the roof and he was using a antenna hole saw, he was on the roof putting all the pressure he could muster telling his boss that this thing sucks, it won't go through. We laughed then he went and explined the way the world works, then they pushed the roof back into shape since it was caved a little.
Stan Glass


Government & Entertainment Division Manager (Kenwood)
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