Motorola XTL2500 - Very poor quality TX

envoy_to_the_stars · Dec 22, 2015

Hello everyone,

I'm new to RadioReference. I tried searching for previous chats about my issue, but I couldn't find anything that caught my eye, so here I go making a new thread.

I have a Motorola XTL2500 380-470 MHZ UHF installed in my Fire Department POV (Chevy Tahoe). It is hooked up to a Laird Phantom 450-512 MHZ UHF antenna. The antenna is hidden behind the plastic cover of the D-Pillar on the Tahoe, to avoid drilling holes in the roof.

Our primary channels run from 451-465 MHZ. I can receive calls from Dispatch fine. When I try to transmit to Dispatch, they can barely understand me through the static. When I transmit on my department issued 5W Kenwood handheld within territory, they receive my message clearly. The Motorola is a 45W radio....so it should be just fine!

I have the code I pulled from the plug, but I do not want to post it publicly. Can anyone offer any ideas as to why I might be getting such poor transmission performance out of the radio? Perhaps mismatched antenna/radio ranges? Could being mounted behind a plastic beam really kill my signal so much that I can't call dispatch from within our territory?

sfd119 · Dec 23, 2015

Your radio antenna is inside your vehicle. It should be outside your vehicle. That would fix your problem.

If you don't want to drill, find a fender type mount.

Thunderknight · Dec 23, 2015

Try temporarily locating the antenna outside the vehicle, with a proper ground plane too. If the problem still exists, then the problem is elsewhere.
But if you have it against the D pillar, it's by metal, it's being detuned. And if you don't have a ground plane under it, it has a poor match as well.

Does the portable work okay from inside the vehicle?

N1GTL · Dec 23, 2015

The other replies are right.

Your running 45 watts into what is not that great of an antenna, right next to a steel pillar? What is the antenna mounted to? Ground plane? Did you check your SWR?

Put a 1/4 wave mag mount on your roof and test it.

jeepsandradios · Dec 23, 2015

Antenna location sucks. Is this a department owned vehicle ? If so drill a hole period. If it is your own and you took the responsibility of being an officer you should be installing the radio properly. Being the antenna is behind the plastic in between the metal structure of the vehicle and the plastic this is to be expected.

radioman2001 · Dec 23, 2015

If you indeed mounted the radio antenna next to the D pillar I suspect you are getting at the very least 50% of you power reflected which can play havoc on any electronic system. Including your cars PCM, air bags system, anti-lock braking system as well as the radio itself, plus also being that close to that much RF is unhealthy, much like being inside a microwave oven. You need to relocate your antenna OUTSIDE the vehicle passenger compartment. All operating parameters of those radios are rated for the antenna to be mounted on the roof or elsewhere not inside the vehicle.

envoy_to_the_stars · Dec 23, 2015

Thanks to everyone for the responses so far. To clarify, the antenna is mounted below the plastic pillar cover highlighted in yellow below. The antenna is mounted on a horizontal metal brace 3/4 of the way up the pillar. It's outside of the body sheet metal, but still very close to it. I have always had a hunch that having such a small antenna trapped next to a metal pillar on 2 sides and a plastic cover on the other two would ruin my performance.

http://i.imgur.com/TbXeXHA.jpg

I believe some of my department's Communications Officers are on RR, so maybe they'll be able to chime in as well. It's my personal vehicle, and while I'm not opposed to drilling holes in the roof, I'd prefer not to. If it comes down to "drill a hole or don't transmit," then I'll start cutting!

Someone mentioned a fender type mount....what is that?

N1GTL · Dec 23, 2015

You have everything going against you. The Phantom antennas are little more than low profile dummy loads that really do not radiate that well. Put it next to the metal body, inside a vehicle...... see where I am going?

Did you test SWR? If not, see if a local ham or communications officer can help with that.

Assuming an NMO mount, can you get a magnetic NMO mount, put your existing Phantom on that and test with it on the center of your vehicle?

The radio is a 45 watt radio you said. How do you know the finals aren't blown and its putting on 50mw?

I'm not giving you a hard time, just saying that there are a lot of variables that need to be explored..... then get a drill out!

KG4INW · Dec 23, 2015

envoy_to_the_stars said:
Someone mentioned a fender type mount....what is that?

This is one, but I'm not sure how well that antenna would work on it, with the lack of ground plane: CVANTPF Instructions found from here: NCG Antenna Mounts

rescue161 · Dec 23, 2015

Why the hesitation? It looks like an ex-police interceptor, so it probably already has holes in the roof. Just look for the rubber plugs. Plus, the vehicle already has a hole in the A-pillar on the driver's side for the spot light. Another hole is not going to affect the value of that vehicle one bit.

kayn1n32008 · Dec 23, 2015

envoy_to_the_stars said:
Can anyone offer any ideas as to why I might be getting such poor transmission performance out of the radio?

Yup. The fact that you have a crappy antenna, mounted inside your vehicle, against the D pillar.

envoy_to_the_stars said:
Perhaps mismatched antenna/radio ranges?

This is possible. AFAIK the Phantom antennas need to be tuned to the segment of the band you are operating in. I would find out what the rated bandwidth of the antenna is for 1.5:1 VSWR.

envoy_to_the_stars said:
Could being mounted behind a plastic beam really kill my signal so much that I can't call dispatch from within our territory?

The plastic is not the problem, the fact that the antenna is on the inside of your SUV, right up against the D pillar is the issue.

Most mobile antennas want lots of free space around them. Any metal that is above the bottom of the antenna, close by, will affect the performance and tuning of the antenna.

Depending on how long this has been going on, you possibly have caused damage to the radio. Get an antenna on the outside of the SUV, properly installed, and check both forward(should be around 45w) and reflected(as close to 0w as you can get it) power.

If you are dead set on not drilling, use a magmount and feed the coax through a door you will not use a whole lot. Another option is to look for a vehicle specific 'L' bracket for the fender. Do not use a friction mount like a lip mount. They are crap.

A fender mount It will be semi directional due to the missing half of the ground plane, and the A pillars/roof being above the antenna, but it will work a whole lot better than what you have going on right now.

Roof mounted, with a minimum 1/4 wave of metal on all sides of the antenna is ideal.

Sent from my iPad using Tapatalk

hitechRadio · Dec 23, 2015

Personally I would go through the roof with a black quarter wave. would look good on that black truck and would be kind of covert, too.

If you ever sold the vehicle they make 3/4 hole plugs.

Not trying to be rude, please don't take it that way....... But since you thought that installing the antenna in that location would work. It makes me wonder if there are other issues also.
You might also let us know how you wired power up to the radio?
To the battery???, fuse box???, How did you ground the radio??? Did you install any splices in the power cable???........Etc.

cmdrwill · Dec 23, 2015

Not to mention, but I will, all that RF getting into your eyes and body..

Motorola XTL2500 - Very poor quality TX

envoy_to_the_stars

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sfd119

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Thunderknight

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N1GTL

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jeepsandradios

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envoy_to_the_stars

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N1GTL

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KG4INW

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rescue161

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