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Low band antenna placement

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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kens
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Joined: Mon Sep 10, 2001 4:00 pm

Low band antenna placement

Postby kens » Sat Jun 10, 2006 10:26 am

I have been mounting antennas for a local utility co. on 37mhz. They do not want holes in the vehicle roof (hitting trees in the area cause cracks in the ant. mount hole) so we usually mount to the pickup pipe rack with an L-bracket and nmo mount (Antenex base load antenna) with a ground strap to the body.
Their latest pickup is a GM midsize and does not have a rack so they fabricated a pipe and flange and bolted it to the bed for the antenna. I mounted to this but cannot match the antenna. The only places that seem to be a match are: center of the cab roof and center of the hood.
Please send your suggestions. Thank you.
Kens

Rayjk110
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Postby Rayjk110 » Sat Jun 10, 2006 12:15 pm

You could try infront of the windsheild, on the far left or right, where the AM/FM antenna is (obviously opposite to where it is installed if installed that way).

I'm not sure if alternator whine/enginge interference would be a problem, but it may work OK there. Give it a shot. Or you could try a ball/spring mount on the side of the truck (like what some of the state troopers do on their cars) or on the bumper as well.

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007
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What radios do you own?: W7 FPP lowband MaraTrac w/AES

Postby 007 » Sat Jun 10, 2006 12:32 pm

What type of "midsize" truck? A Colorado?
Do not make Sig angry...he'll just keep ringing the bell.

Birken Vogt
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Postby Birken Vogt » Sat Jun 10, 2006 2:28 pm

Not sure if this is any help but when I get an antenna that is a pain to match or unknown, I look at it with a network analyzer and transmission/reflection test set. By viewing the return loss, I can see what the best SWR is going to be, and if the antenna system is going to work at all.

We have one company that still uses 45 MC extensively here, and I second the idea of using a ball mount and 1/4 wave whip if height will allow. Nothing beats a full size antenna. However we are having to look long and hard for ball mount springs that have a braided strap inside them any more believe it or not! Cheap Chinese imports do not have the strap a lot of times and it causes all sorts of havoc with the match.

Other than that the obvious: is the antenna mount that they made well bonded to the truck box.

If you have any questions ask, we still deal with a lot of low band at my shop.

Birken

niagara16
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What radios do you own?: motoola

Postby niagara16 » Wed Feb 07, 2007 7:44 pm

we have a utility company that wants the same absolutly no holes in there trucks. we had a special bracket fabricated for them and they mnt on the hood hing. i'll get a pic of it for you

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HLA
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Postby HLA » Thu Feb 08, 2007 5:22 pm

your biggest problem is going to be the ground plane area, you can run all the ground straps you want but it's not the same as the surface area and low band needs the biggest ground plane. all you can do is try several places with a meter on it and see what kind of rejection you're getting.
HLA
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Jim202
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Postby Jim202 » Fri Feb 09, 2007 5:22 am

Many utilities get their vehicles under a lease program. This is
where the no holes stand comes from. It may be a fabrication,
but they are the customer.

As was already stated, low band antennas want to have a
ground plane under them. In many cases this is hard if not almost
impossible to obtain.

It will take some playing around till you find a spot and antenna
that will work.

Jim

WB5ITT
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Postby WB5ITT » Fri Feb 09, 2007 6:50 pm

Jim202 wrote:Many utilities get their vehicles under a lease program. This is
where the no holes stand comes from. It may be a fabrication,
but they are the customer.

As was already stated, low band antennas want to have a
ground plane under them. In many cases this is hard if not almost
impossible to obtain.

It will take some playing around till you find a spot and antenna
that will work.

Jim


Worked for GSU before and after Entergy took over..our system was 48MHz lowband with leased vehicles...ONCE, our garage wanted us to quit drilling holes..We made our own test range and did measurements (roof mounted, L bracket mounted, even glass mounted!!)...and sure enough, there was as much as a 20db difference in radiation (the glass mounts fell off the glass after a minute of 100watts...a dummy load was almost as good a radiator!)...btw we even tried the DDRR lowband antennas..I mean WE tested EVERY possibility...the roof mounted 1/4 base loaded (NMO style) was best overall...the 1/4wave whip and ball mount was a close second (overall pattern was NOT as clean as the roof mount). THEN we found out after 150,000 miles, one antenna hole meant NOTHING at auction, etc....
NOW I work for another utility...we lease all our vehicles...and yes, I DRILL holes for roof mounted antennas (UHF this time ;) Entergy also drills and mounts NMO 800 MHz antennas...(we went 800MHz trunking in 95 and I left Entergy in 96).
A hole in the roof for a 1/4wave base loaded? Do it if you can! anything else is not worth the effort or worry...

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HLA
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Postby HLA » Sat Feb 10, 2007 6:58 pm

maybe a very very very heavy duty magnet mount and you can still get it on the roof in the middle with a good ground plane? i've seen some that have 3 separate magnets in a triangel with the antennae in the middle. it's a hard call to make, either drill holes and save the wear on the radios or a ghetto mount and damage the output stage of the radio?
HLA
I never check PM's so don't bother, just email me.
I won't reply to a hotmail, gmail, aol or any other generic free address, if you want me to reply use a real address.
STOP ASKING ME FOR SOFTWARE OR FIRMWARE, I JUST FORWARD ALL OF THE REQUESTS TO THE MODERATORS

k2hz
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Postby k2hz » Sun Feb 11, 2007 10:21 am

I am very amused by this discussion. I retired from a utility a few years ago and I thought it was only our fleet supervisor that had this no antenna holes obsession.

His mechanics were allowed to hack a ragged hole, run wires with no grommet and plug the hole with duxseal for light bar wiring and employees were allowed to install their own broadcast radios and antennas but we had to mount our 2-way antennas on ladder racks, etc.

I could respect the need for some no-hole solutions on leased passenger cars but the no-hole policy applied to company owned line trucks, vans and construction vehicles that were run until the body rusted out.

I had to attend a high level meeting to address employee compliants of poor radio coverage in some vehicles. I expressed my opinion that we could make a dramatic improvement at little cost if we were allowed to do proper antenna installations. The transporation supervisor immediately went ballistic and said that holes from radio antennas reduced the trade in value of a vehicle by 2000 to 5000 dollars! I said that in my 40 years in 2-way service I found that an antenna was either a non-issue at trade in time or could be fixed for about $100 worth of minor body work. I also said a well installed NMO mount on a commercial vehicle could be an asset not a liability. I immediately got shot down by the supervisors VP who said I has no right to question their expert on vehicles. My VP asked to see documentation of the effect on trade in. The transportation people got a letter from a dealer that said a recent trade was $2000 below book due to "the condition of the vehicle", no mention of the antenna.

The other problem we had with the transportation people is that they said they could not wait for us to remove a radio when a vehilcle was being traded in. I made a promise to have a radio tech remove the radio the same day we were notified but they continued to not call us and just give us the trunk mount unit and control head minus the mountings and with the cables cut. They could not even be bothered to unplug the connectors.

So, this meant we had to buy hundreds of dollars of new cables and accessories to reuse the radio. But, management thought this was less important than the alleged "damage" we would cause by properly installing antennas.

I thought it was just my former employer with these weird ideas but it must be something more prevalent in the utility industry.

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Paul
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What radios do you own?: You can't imagine!...

Postby Paul » Tue Feb 13, 2007 11:27 am

Nice to see that people around the globe face the same problems with you.
I also thought that this no-hole-antenna-mounting was a local fetish!
Favorites hear are some el-cheapo nickel plated lip mounts.
Thanks god, the cable is always damaged on the bend; not bad to ask for $150 to replace the PA module.
(I earn money by selling Motos & servicing Icoms!)
It is curious that they never complain about the rust that develops under the mount...
There are 10 kind of people: Those who understand binary and those who don't.

StanComm
Posts: 40
Joined: Fri Oct 26, 2001 4:00 pm

Lo-Band antenna choices.

Postby StanComm » Fri Mar 23, 2007 8:48 pm

Hello all:

Once had to install a 47meg radio in a Mack tow truck. The whole cab was fiberglass with some metal reinforcement. But, no metal where it counted.
Tried the ground strap idea... NG!
Tried several brands of antennas; Antenex "C" coil, Motorola Spectrum, Cushcraft Signals... The Antenex came the closest to a usable match.
Finally had to add a single wire counterpoise attached to the base of the antenna on the ground side of the NMO mount. Curiously, the wire did NOT have to be extended, it wound up being put into a 6" coil up on the roof of the cab, right inder the light bar.... works to this day.

Stan

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Bat2way
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Postby Bat2way » Mon Mar 26, 2007 8:28 am

On the same note...a customer's employee who was an "expert" CB'er, expected a low band whip to be welded to the bumper for "better coverage". I didn't even ask what about the hatch and tailgate.........

niagara16
Posts: 30
Joined: Fri Feb 02, 2007 4:06 pm
What radios do you own?: motoola

Re: Low band antenna placement

Postby niagara16 » Sun Dec 30, 2007 8:22 pm

Here is a gound question for antenna placement. I am doing a install on a 2008 freightliner dump truck using a lowband radio at 36mghz. have any ideas where to place the antenna's? the mounts for the mirror's are plastic and the compnay wants no holes drilled into the vehicle. the rest of the body is fiberglass...

StanComm
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Re: Low band antenna placement

Postby StanComm » Mon Dec 31, 2007 12:05 am

Boy, they don't want too much, do they?
If the whole cab is fiberglass I'd be worried about the signal, whatever might actually get out of the antenna, getting into the vehicle's wiring. Even the Diesel engines are just about fully computer controlled. Saw a 40 watt uhf radio get into the "water in the fuel" sensor. Turned out the sensor was defective... but still...
Might be wise to talk to the folks they got it from. See what they recommend, or see if they have a tech department which can say more than just, "No way, it can't be done!"
As per my last post on this subject, you'll need at least one counterpoise wire, no matter where you do manage to mount the whip. Otherwise tuning it will be near impossible.
What comes to mind... and it's not pretty, would be to find some sort of clamp arrangement and mount the whip, a full quarter wave guy, on the end of the front bumper... assuming that when the hood is tipped open, it doesn't completely cover up all of the bumper. Naw, that puts the engine wiring right in the near field... bad idea! (Was up to the Hill Country today and the Mountain Cedar pollen is dense... so now I'm high on Benedryl.)
Best bet is to bracket mount it near the top of the cab's rear vertical wall, assuming that the dump box doesn't interfere. Four small holes, three for the screws and one for the cable. If you can get to the inside of the fiberglass back, make use of some body washers on the nuts n' bolts, to keep cracking to a minimum. Connect your counterpoise to one of them. That will apply to a mirror mount too.

Stan

niagara16
Posts: 30
Joined: Fri Feb 02, 2007 4:06 pm
What radios do you own?: motoola

Re: Low band antenna placement

Postby niagara16 » Thu Jan 03, 2008 8:29 pm

Thanks foir the input, but i mounted the antenna up by the windshield on the passenger side found some metal and took angle bracket and mounted it nicely wasnt able to get it tuned perfectly but got it down to reflective of 4 with 75 out.


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