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XTL2500 Problems and more!!

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emtunderwood

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Hello,

I'm installing a Motorola XTL2500 VHF in a 2002 Pierce Dash Fire truck and have ran into some problems. This will be lengthy but should give you the information that you need hopefully to help us at the department out.

We purchased this truck and it had XTL2500 remote system installed but was removed before we received the truck, the old system was a 800MHz system we are VHF. Now mind you when they removed the old system they basically cut everything and left it hang what they couldn't reach. We have identified the 3 antenna mounts in the truck and placed antenna accordingly even replaced the coax to be on the safe side and made sure there is no resistance on the lines and new connectors. We have 2 systems in this truck. One being a VHF remote mount 110w and a UHF single unit 55w, and spaced the antennas one on one side of the cab and one on the other about 96in. apart.

The problem we have ran into is on the VHF with the truck off everything works great, crystal clear and even the setcom system is crystal clear. When we start the truck the setcom system is crystal clear in cab but when we transmit on the radio we get a loud hum and no voice. So we re-ran all the power and ground cables again, put a in-line filter on the power and still the same problem. We contacted pierce and motorola both and went through the wiring again. Pierce has dedicated places to hook up the power to the radio, power to control head and ignition power. The radio first was wired the way they said to wire it, radio to direct power, control head to switched power and ignition sense power to ignition lug and ground to ground. Ok, that worked until the truck was started. Then the same thing occurred just a hum. We checked the regulator on the alternator and was putting out the right voltage idling and at high idle around 1500rpm. We did find that 4 of the 6 batteries were bad and they have been replaced all 6 of them. Still wiring the radio up the way motorola and pierce both said to wire the radio into their wiring housing we still get the hum when the truck is running.

So called motorola and piece back and advised the same thing and they stated they system can be ran directly off the batteries. We done that, wired the radio directly to the power and control heads to the switch and ignition to ignition. Ok, fired the truck up transmit and it works with all lights and sirens running its great. However, heres another problem, the radio itself is warm constantly. I understand its getting power constantly from the batteries. Is that ok?

But even more problems the radio is set to 110w transmit we are only getting about 85-88w with a reflective power of 20-26w fluctuating wether the truck is running or the batteries are on its the same. I don't know what is causing this. We checked with a ac/dc power box and it reads 109w output with still 20-26w reflected. checked the coax and mount and ground and still 20-26w reflected.

I know this isn't right. I've called local radio shops and they have said they have no clue what could be causing this even if the power is ran directly from the batteries and has 10g wire for hot and grounds, new coax and antenna and no resistance on the antenna, we shouldn't have the VSWR that we have and we should be getting the full power.

I don't know what to do to fix this. I even took the radio to the shop and they bench tested the radio and it tests out actually higher than normal so it is a good working radio. Motorola wanted the codeplug so they can make sure everything is right on that end. So got a all clear from them on that, everything is programmed correctly.

I just don't know what else to try to fix this power problem or to rewire the power and ground and the VSWR issue, if I need to put some sort of filter on the antenna and coax. We already have a line filter on both radios, control heads and even filtered the grounds to both radios.

Does anyone have any idea how to remedy this problem? If you need more information shoot me a message and I'll get back to you..

Thanks
 

cmdrwill

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radio is set to 110w transmit we are only getting about 85-88w with a reflective power of 20-26w fluctuating "
That seems to be a bad or incorrect antenna. That reflected power is way too much, and could be causing your problem. Did you test the radio into a known good dummy load?
 

FedFyrGuy

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Coax and connectors replaced. I agree with cmdrwill - try a different antenna. A simple 1/4 wave cut to frequency will do....
I found a UHF XTL in a fire truck a couple of years ago that was connected to a VHF antenna and it was still working though....go figure.
 

mmckenna

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Coax and connectors replaced. I agree with cmdrwill - try a different antenna. A simple 1/4 wave cut to frequency will do....
I found a UHF XTL in a fire truck a couple of years ago that was connected to a VHF antenna and it was still working though....go figure.
A 1/4 wave VHF antenna is 3/4 wave on UHF, and while they'll have a funky radiation pattern on the UHF band, they'll tune up quite nicely. I used a 1/4 wave VHF antenna for years on a dual band amateur radio. When looking at SWR, it was actually lower on the UHF band than it was on VHF.

The radiation pattern you get with a 3/4 wave is directed pretty high above the horizon. Not ideal, but it does work.
 

mmckenna

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Has the antenna been properly tuned for your operating frequency?
Your reflected power is pretty high. It's close to 3:1 which is bad. That will cause the radio to heat up when transmitting.
If you are getting enough RF bounced back towards the radio, that can cause issues like you are experiencing.
High SWR can be caused by a number of things:
Improperly tuned antenna
Too close to another antenna or reflective source
damaged coax or connector

I think you need to trouble shoot your antenna system before you do anything else. That is an obvious issue.

Next, you need to make sure everything is properly grounded. Do not rely on the negative power lead or antenna mount ground as the primary ground for your radio. Install a ground wire from the radio chassis to a nearby body ground. Keep this lead as short as possible.

Make sure all your DC power connections are good. Do not rely on old wiring unless it's been fully checked out.
 

emtunderwood

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Ok. On the top of this truck there are 3 antennas.. The one above the driver is the VHF, center antenna mount is empty, has a cap, coax is rolled up and tucked in the headrest, passenger side is UHF.

VHF antenna - Laird QWB152 (my mistake from earlier) cannot cut it.
UHF antenna - PCTEL Maxrad BMWU4002S 380-470Mhz

Both are spaced 24in apart. The mounting locations are factory from pierce.

Installed new antenna and connector. No kinks or cuts. and total run is 14ft.

The radio is on a rubber mat. Motorola and pierce both said not to run a ground from radio chassis to master ground or chassis mount, said something about creating a ground loop that would cause interference. But I'll try it. Only other option I could do is take the regular coax cut the PL connector off and put a mini uhf on there instead of using a PL-259 to mini-UHF jumper.
 

mmckenna

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VHF antenna - Laird QWB152 (my mistake from earlier) cannot cut it.
It can be cut.
While a wide band antenna should be fine if your frequencies are within it's designed operating area, it should still be checked and cut. The amount of reflected power you are getting is WAY too high. Usually you want it below 2:1, and much closer to 1:1 if at all possible. Yours is close to 3:1 which indicates a major problem. You should not be operating the radio with the SWR that high. There is something wrong and it needs to be fixed.
These sorts of issues are not easy to fix with just an SWR meter. Ideally you need someone with an antenna analyzer to look at the antenna system to find the fault.
Might be that the center pin of the NMO is not making good contact. If the mount was not installed correctly or there is an issue with the antenna base, this could be the issue.
If the antenna was not assembled well, is damaged, etc. that could be the issue.
Whatever is wrong, it needs to be addressed before you do any more transmitting. What you have now is not acceptable.

I'll add that it is important that the truck is out of the bay when you do the testing, if it's in the bay, there can be enough reflection to cause issues.


Installed new antenna and connector. No kinks or cuts. and total run is 14ft.
OK, 14 feet, not an issue. What I would suggest is removing the antenna off the mount. Disconnect the connector off the back of the radio.
Using a multimeter, check for continuity between the center pin of the coax connector and the outer shield, there should NOT be continuity. If there is, there is a short circuit somewhere and that needs to be fixed.
Using the meter again, check the following:
Check center pin of the coax to the center pin on the NMO mount. There should be continuity.
Check the outer shield of the coax connector to the outer ring of the NMO mount, there should be continuity.


The radio is on a rubber mat. Motorola and pierce both said not to run a ground from radio chassis to master ground or chassis mount, said something about creating a ground loop that would cause interference. But I'll try it. Only other option I could do is take the regular coax cut the PL connector off and put a mini uhf on there instead of using a PL-259 to mini-UHF jumper.
No, this doesn't make sense. Grounding is important to radio equipment. Ideally everything needs to be at the same ground potential. Isolating the radio from ground doesn't make sense. But, I think your issue is with antenna.
 

emtunderwood

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Ok. I'll check that. Our frequencies are RX: 156.105 and TX: 159.525 and when new radio system goes in it will be 159.000. What antenna do you recommend? Also, on the new mount the inside portion of the mount is flush with the outside cab and primer has been sanded down on the inside and it is seated well, there's no play it's good and solid. The ring that fits down to secure it to the outside roof is good and snug. I looked under the cover and everything seems to soldered correctly. I will check the continuity here shortly. And I will go ahead and run a short ground from the radio chassis a master ground site behind the passenger seat its only about 18in. from the radio.
 

FFPM571

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Also the PL259 to mini UHF can cause issues. We always change to the correct connector My shop gets plenty of Used emergency vehicles that we refurbish and reinstall equipment
 

mmckenna

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Ok. I'll check that. Our frequencies are RX: 156.105 and TX: 159.525 and when new radio system goes in it will be 159.000. What antenna do you recommend? Also, on the new mount the inside portion of the mount is flush with the outside cab and primer has been sanded down on the inside and it is seated well, there's no play it's good and solid. The ring that fits down to secure it to the outside roof is good and snug. I looked under the cover and everything seems to soldered correctly. I will check the continuity here shortly. And I will go ahead and run a short ground from the radio chassis a master ground site behind the passenger seat its only about 18in. from the radio.
That should be a good antenna. If I was going to recommend one for fire service, a good wide band quarter wave is what it would be.

For those frequencies, that antenna should be correct if it's the right length. Quarter wave, even non wide band ones, are very broad banded. I have a basic Larsen quarter wave on top of my pickup. I put it on my analyzer at work and it's got 2.0:1 SWR all the way across the VHF high band, from 144 to 174.
Unless your antenna is the wrong length, or there it is damaged, it should be giving you good results.

What I found when I did an install on a Pierce engine many years ago was that the wrong NMO mount had been installed, that was the fault of the installer, not anyone else. Anyway it wasn't allowing the center pin of the antenna to make contact with the base. From what you described, the outer ring being flush with the center, that should be OK.
One test you can do is to leave the antenna on the mount, and check for continuity from the whip to the center pin of the coax connector. There should be continuity. If there isn't, I'd suspect the base of the antenna isn't allowing the center pin/tab of the antenna base to make contact. You can sometimes fix this by taking the gasket off the antenna base. If that doesn't fix it, try another 1/4 wave antenna or get a "thick mount" NMO.
 

mmckenna

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Also the PL259 to mini UHF can cause issues. We always change to the correct connector My shop gets plenty of Used emergency vehicles that we refurbish and reinstall equipment
Yeah, good point. You are not using any adapters, are you?
Those mini-UHF adapters can cause issues. They'll put a lot of strain on the antenna connector of the radio. Ideally you want the mini-UHF connector on the coax to match up with the radio. Avoid any adapters, if you can.
 

emtunderwood

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There was a PL-259 to mini-uhf adapter in the box when we received the radio thats what we used. I have some mini-uhf connectors I will put one of them on.
 

mmckenna

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I think that would be a good idea.
I've seen more Motorola radios with busted off mini-UHF antenna jacks from people using adapters. I seem to remember Motorola specifically warning against this. In fact, they sell an adapter cable that is the recommended means (after using the right connector) It's basically a 6 inch length of coaxial cable with a mini-UHF male connector on one end and either a female N or female UHF on the end.
This takes the strain off the antenna connector.
 

N4KVE

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I think that would be a good idea.
I've seen more Motorola radios with busted off mini-UHF antenna jacks from people using adapters. I seem to remember Motorola specifically warning against this. In fact, they sell an adapter cable that is the recommended means (after using the right connector) It's basically a 6 inch length of coaxial cable with a mini-UHF male connector on one end and either a female N or female UHF on the end.
This takes the strain off the antenna connector.
In my car, I use NMO/coax assemblies that have mini UHF connectors from the factory. But in the base, I use the above mentioned adapters. Moto part # HKN9557A. They can be found on E-Bay.
 

emtunderwood

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So Far So Good

Ok, checked the continuity of the coax on the ground, sheath and center pin, All Good. Checked the VSWR outside with everything running, lights and all got a Ratio of 2.49:1 Changed the jumper from PL-259 to mini-uhf and re-crimped on a mini-uhf and rechecked continuity all good. Now have a VSWR of 1.86:1. And I will be changing the antenna to a better antenna.

Does this sound acceptable?

What recommendations for a antenna would you suggest?
 
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