Help with mounting VHF 1/4 wave on trunk.

[scanner1]

At work, we recently moved to a VHF repeater from lowband and we had all vehicles outfitted with 1/4 wave 18" antennas. I was wondering if there is an opinion here on where the proper location for a 1/4 VHF ship should be on a rear trunk.

The reason I ask? Some of the cars have the antenna mounted on the front of the trunk, near the rear windshield. These vehicles I have found to have horrible reception, both TX and RX.

The rest of the fleet has the antennas mounted more towards the rear of the trunk and away from rear window. I have found these vehicles have excellent reception.

Radio tech is saying it doesn't matter where they are mounted.

I thinks he's wrongs, what does everyone else think??

[gewecke]

If these antennas were tuned properly to the frequency your repeater is on,then it would make very little difference if they're at the center of the trunk or near the center of the rear window. If they are all measured at 18" exactly then I suspect your tech just slapped these on? You may want find out if these antennas were tuned.
N9ZAS

[RadioDaze]

Q to antenna gurus: Can its proximity to a rear window defroster grid have any effect on it? (Assuming that the defroster is turned off.)

I ask this because the defroster grid is not simply grounded metal, but also coupled to the positive wiring, esp. when it's running.

[prcguy]

Yes the rear window defroster wires can interfere a bit with the pattern but it should not be drastic. Are the antennas like 6" away and the rear window is mostly vertical or is it a foot away and the window slants a lot? Is the range good with the car facing away from the repeater and bad the other way or is it bad in all directions?
prcguy

[scanner1]

The fleet are crown vic's with both defrost and am/fm elements in the rear window. I know that the cars with the VHF antennas mounted closest to the window have horrible reception, where the cars with the VHF antennas mounted near the rear of the trunk have excellent reception.

Im thinking the cars with bad reception either need to get 1/2 or 5/8 wave antennas, or simply have the antennas moved to the rear of the trunk.

The coax is new with new NMO mounts, so I don't really think that would be a factor.

[jim202]

There have been threads on just this topic for many years. Some of the radio techs have found out
from playing around with the fleets they maintain, that mounting the antenna right in the center of
the trunk lip up against the rear window was not the ideal location. Moving the lip mount antenna to
one side corner of the trunk lip worked much better.

Second best location is to drill a hole in the trunk and mount it right in the center of the trunk.

Best location is up on the center of the roof of the vehicle. If there is a light bar, make sure your
at least a 1/4 wave away from the bar on the roof. Do not mount it right up close to the bar.
Have seen some of the shops mount the antenna up on the top of the light bar on the metal
center piece. However, this might limit the servicing of the light bar. Depends on how it was
constructed. Plus you don't get enough of a ground plane under a VHF antenna on the light bar.

Another good point to keep in mind, some of the solid state power supplies used on the strobe
lights cause a good deal of noise to some radios. So I am not a supporter of the antenna and
light bar being common partners.

Just my 2 cents and the radio techs will do as they please anyway.

Jim

Originally Posted by scanner1

At work, we recently moved to a VHF repeater from lowband and we had all vehicles outfitted with 1/4 wave 18" antennas. I was wondering if there is an opinion here on where the proper location for a 1/4 VHF ship should be on a rear trunk.

The reason I ask? Some of the cars have the antenna mounted on the front of the trunk, near the rear windshield. These vehicles I have found to have horrible reception, both TX and RX.

The rest of the fleet has the antennas mounted more towards the rear of the trunk and away from rear window. I have found these vehicles have excellent reception.

Radio tech is saying it doesn't matter where they are mounted.

I thinks he's wrongs, what does everyone else think??

[gewecke]

Originally Posted by RadioDaze

Q to antenna gurus: Can its proximity to a rear window defroster grid have any effect on it? (Assuming that the defroster is turned off.)

I ask this because the defroster grid is not simply grounded metal, but also coupled to the positive wiring, esp. when it's running.

That's a really good question. I never thought about it,but then I've mostly driven trucks where that's not a problem.
N9ZAS