I have a Antennax 1/4 wave on my police cruiser with a trunk lip mount. Our system is VHF 155. I am not getting the range I like, so I would like to go to a taller antenna. Can I use my existing mount and just order a longer antenna? If I do, is there anthing I need to check or set? Is it as simply as switching them? ( I am guessing not )
VHF antenna question
- Thread starter k9gunner
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mjthomas59
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- Nov 29, 2006
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It depends on if you have a standard nmo trunk lip mount or not. If you do then all you need to do is buy a 5/8 wave vhf antenna and it will come with instructions on how to cut it for the frequencies you plan on transmitting on.
I would also suggest using a swr meter to ensure that the antenna is cut properly and that you aren't risking any damage to your radio.
I personally use a Larsen 5/8 wave antenna and it works awesome, but honestly the tram, and many other manufacturers antennas are probably just as good.
I would also suggest using a swr meter to ensure that the antenna is cut properly and that you aren't risking any damage to your radio.
I personally use a Larsen 5/8 wave antenna and it works awesome, but honestly the tram, and many other manufacturers antennas are probably just as good.
k9gunner said:
It's not that simple.
Gain and radiation pattern are two different things.
If your VHF system uses repeaters that have any type of elevation, then the 1/4 wave antenna with it's higher radiation pattern is more appropriate.
If your system is simplex, or you're in the mid-west where it's really FLAT, then a 1/2 or 5/8 wave antenna is more appropriate because it keeps more signal at the horizon.
i had the opposite problem on my fire engines. They were city hand-me-downs with 5/8 wave antennas.
I had to swap them out for 1/4 waves because we operate rural with high-level repeaters and I needed the higher angle of radiation.
YMMV
We are on all repeater channels, and in Ohio there are some hills. I work in a fairly rural county, and our city sits somewhat low compared to the rest of the county. I just notice that as soon as I get out of the county I loose RX. I have not tested the TX, but TX does no good if i cant recieve.
hoser147
Member
K9 does your Dept have a radio service contractor that does your radio work? Most do you might want to consult them on this issue..........Hoser147
RayK
Member
If you use a mag mount behind the lightbar it will affect the radiation pattern, would probably make things worse. Try to see if you can mount the antenna on the lightbar??
RayK said:
Which is usually aluminum (ours are) and poorly grounded.
Also a bad idea.
The cheapest fixes to test are:
Buy and cut a 5/8 wave vhf antenna. Any good quality like Maxrad or Antennex.
Buy a COMMERCIAL quality mag mount with decent coax and try it on your roof.
The antennas on my fire trucks are mounted aft of the lightbar, nmo mount
drilled through the roof.
California Highway Patrol runs the same setup on low band. Aft of the lightbar
nmo drilled through the roof.
Sounds like you are mostly rural and want to keep your signal near the horizon.
Go for a 1/2 wave or 5/8 wave gain antenna first and give it a try.
I've gotten some surplus Antennex stock on Ebay pretty cheaply. New in box. You just
have to set up a search.
Trunk mounts suck for pattern.
BTW what are you using for a radio ?
RayK
Member
I would never recommend using a lightbar or even a roofrack for a grounding point. One reasion the trunk lip mount is used is that many PD lease thier fleet and the lease doesn't allow for permant mount of other than factory installed equiptment. Many times the trunk lip mount is used to easily remove the antenna & radios when a the fleet of autos are replaced
k9gunner said:
You really do NOT want to run a magmount with a high power radio.
Try an antennex or maxrad 1/2 wave or 5/8 wave NMO antenna on your
current trunk lip mount and see how it works.
Also make sure that mount is properly grounded (no rust), and that the trunk
has a ground strap from trunk lid to frame.
Sorry, but I guess that is what I get for living in CA. I have NEVER heard of
a PD leasing a vehicle before.
They drill so many holes for equipment here, they look like swiss cheese when they
go to auction.
If a magmount is your only option to get the antenna in the center of your roof then I agree with the others, using it on a 110w radio is asking for trouble. Your best bet for improvement would be the 5/8 wave gain antenna on the trunk lip mount behind the center of the windshield. If you can find a way to get a an NMO mount drilled in the center of the trunk, that would be even better. It's not hard to drill a trunk and you only leave a small hole plug when it's removed.
PS - Like Trooperdude, I guess I had it good working in California, where we had a radio shop that did everything we need ( some things we didn't need
). You really need to talk to your chief about this issue. A street cop shouldn't have to be figuring out what kind of antenna or radio to use.
PS - Like Trooperdude, I guess I had it good working in California, where we had a radio shop that did everything we need ( some things we didn't need
). You really need to talk to your chief about this issue. A street cop shouldn't have to be figuring out what kind of antenna or radio to use.- Status
