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Low Profile Mobile Antenna Help

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Wackodrumr

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I'm getting a car that's going to have low profiles mounted on the roof. I'll mostly be operating on the commercial VHF/UHF bands for work. But for fun, I'm planning on programming in the ham 2m/7cm bands into my radio as well (yes I'm a licensed ham).

Since I'm limited to having low profiles, which most only operate in the 150 mhz and 450 mhz range, will it hurt my radio to transmit in the ham bands using the commercial band antennas?

We mostly use the Laird Phantoms for low profile antenna to give you an idea on what I'll be using.
 

mmckenna

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"Hurting" your radio depends on a number of things. Some radios will automatically throttle back the RF power to protect it, some will not.

I can tell you that the low profile VHF antennas are VERY narrow banded. If you are going to use it at 150MHz for work, that's likely where it will be tuned. It's going to have high SWR on the 2 meter amateur band.
High SWR will cause issues.

The issue is that it's very difficult to hide a 1/4 wavelength VHF of antenna in something the size of a soup can. It's a bit easier on UHF, so you may get favorable results, you may not.

The VHF low profile antennas are, as I said, very narrow banded and not capable of handling a lot of power. Everyone (and I -do- mean everyone) I know who has tried on of these low profile VHF antennas has used it for a little while, and quickly replaced it with a 1/4 wave. I've been offered a few of them for free.
Where they do work is on single or very closely spaced frequencies at reasonable power levels and over short distances.

I'd also challenge the "low profile" claim. I haven't seen a VHF "low profile" antenna that was very low profile. Always looks like someone painted a tin can and stuck it on their vehicle. I've found a 1/4 wave antenna is a lot less noticeable and they have the benefit of being very wide band. I've put standard $9.00 VHF quarter waves on antenna analyzers and with a proper ground plane they'll do 2:1 or less from 144MHz well up past 160MHz.

If it's not too late, see if you can get them to install standard 1/4 wave antennas on the vehicle.
 

12dbsinad

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I am one of those people who have tried a phantom and quickly replaced it with a quarter wave. mmckenna hits the nail on the head in regards to these antenna's.
 

prcguy

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I have a couple of Laird Phantoms and they are really terrible antennas. They will not even cover the FM part of the 2m band without going off the VSWR charts. They cover about 1MHz then its off the cliff.

Going from a 1/4 wave whip to a Phantom is like night and day in performance, its like where did all the 2m repeaters go? I cut one open and its a piece of roughly 1/8" thick fiberglass circuit board about the width and length of the housing with a spiral trace that goes around the board. I should post a picture, its really cheesy.
prcguy
 

N0ZQR

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The laws of physics can't be broken now matter how the ad people try!

Ron
 

AK9R

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A black 1/4 wave VHF whip mounted on a trunk lid, while not the ideal position on the vehicle, can still be pretty stealthy.
 

N4KVE

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I use the Laird/Antennex version for UHF. Sits in the middle of my trunk lid. They make them in the 430-450 for hams, & the 450-470 range for commercial use. I use both, but one radio I need for GMRS, & ham, so that radio gets the 450-470 antenna. I haven't measured SWR, but transmitting at 447 on the 450-470 antenna seem to work just fine, & when I travel to Miami, I can get into the Delray repeater 60 miles away just fine. Similar results on 900 with their 900 antenna. I have no VHF equipment, so I can't comment on the VHF antenna.
 

n3obl

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Phantoms work fine for uhf and higher freqs. VHF and low profile don't go together. Best thing for vhf that's low profile is a thin whip quarter wave antenna. Now they make dual band antennas that are around that length and can work well.
 

Rred

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To keep your employer and your radio happy (you don't get a vote) you could contact the antenna maker, or ask the radio shop if they have specs, to see what SWR that antenna will product on the ham bands. Then check your radio maker to see how the radio will tolerate it.

Or, buy a $35 SWR meter, hook it up to your radio, then the antenna, and see what it has to say about SWR.

As to your vote? You're rolling the dice if you just hook up and see what happens. If the SWR is too much for the radio and the finals blow, your first hint of that will be the dead radio.

Just saying.
 

AI7PM

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I use this with an NMO mount: PCTEL 136-174 1/4 Wave Antenna w/ Spring, Black (BMWV1365S) from Solid Signal

It is a broadband VHF antenna, which facilitates my CAP and ham operations, and if I want then I can take the spring whip part off and just use the bottom part which is simply a low-profile VHF Part 90 antenna like you stated you have with an attachment point for the whip.
OK, I looked at the specs on that antenna. Seems to me, if you remove the whip and spring, all that's left is the base mount. No resonant (by design) parts. Please correct me if I'm wrong.
 

K4RMN

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OK, I looked at the specs on that antenna. Seems to me, if you remove the whip and spring, all that's left is the base mount. No resonant (by design) parts. Please correct me if I'm wrong.
I'll have to look at the packaging for the one I have, must be slightly different then because I've used it with just the base on VHF Part 90 frequencies perfectly fine.
 

FFPM571

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OK, I looked at the specs on that antenna. Seems to me, if you remove the whip and spring, all that's left is the base mount. No resonant (by design) parts. Please correct me if I'm wrong.
You would be correct. That antenna by design is not supposed to have the spring or whip removed.
 
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Black antennas blend in better for stealthier installs (I've never had chrome antennas on my vehicles because…well my professional opinion of the auto industry is that chrome has become the herpes of the industry).

PCTEL makes a wideband UHF knob…430-480 MHz. You'll never notice the difference between it and a UHF 1/4 wave antenna (if you are still going for the LP thing).

I'm very fond of the Sti-Co Flexiwhip for VHF installs…especially when you know you will potentially be hitting things…but a .100" diameter black NMO antenna will work just as well if you aren't planning on hitting anything (and is a fraction of the price).

One thing to keep in mind about Low Profile knobs…unlike 1/4 wave NMO antennas (of the original Motorola design) they do not bend. So if you are aiming for LP for an SUV to fit into an older home's garage or something like that…measure that thing at least twice before you drive in. Know a guy who's roof needed replacing after he missed judged by 1/2" and drove into the garage…
 

lmrtek

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"Compactenna" claims 400- 500mhz coverage with their 4 inch tall antenna

Universal Radio sells them
 
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