Help with issue, possibly antenna

[Jfox642]

Hope someone can help me here. I have an Motorola xtl5000. My antenna is a liard 55” whip mounted on the headache rack of my truck. When I ordered the antenna is was advertised at “no ground plane” and “pretuned”.

First, I use this for fire/ems. We are VHF conventional analog and digital frequencies ranging from 154-158 “ish”.

My issue is receiving and transmitting. I have no idea what my issue may be. Unless I’m with in a few miles of the main repeater site it is choppy and static and I can’t hear crap. I switched to a glass mount antenna like my wife has on her Durango (which works amazingly well and clear 30+ from the repeater) and had no improvement. So I switched back to the 55” antenna.

The radio in my wife’s Durango is a Motorola Astro Spectra. I checked programming with her radio vs my radio and all is same.

Does someone out there have any ideas for me, cause I’m stumped.

 

[mmckenna]

Mounting any antenna on the headache rack is likely to be an issue. While the antenna does not -require- a ground plane, it will work better with one. Having the antenna mounted there is going to give it a very lopsided ground plane and thus a lopsided radiation pattern.

I would not trust "Pre-tuned". Tuning will change slightly depending on how/where it is mounted. SWR being a bit high isn't going to be a huge problem and probably not the cause of your issue.

The glass mount working 30 miles on your wife's car means that the repeater is probably OK and your wifes setup is good.

I would start looking at your entire installation carefully:
-Make sure radio power is getting good clean 12 volts.
-Positive power lead needs to go directly to the positive terminal on the battery with a fuse installed as close to the battery as you can reasonably get it. Any other power source (cigarette lighter, tapped fuse, etc) is all going to give you problems.
-Negative lead should be grounded to the vehicle chassis close to the radio. Don't run it all the way back to the battery, as that will bypass the sensor on the negative lead and will confuse the power management in the newer trucks. It also gives you a good local ground.
-I would really, strongly, suggest having the antenna permanently installed dead center of the cab roof. This will give you a proper ground plane, proper ground connection, and much better performance.
-Running coax through doors/windows, or however you got from the cab to the headache rack might be an issue. Cable getting pinched/damaged will cause problems.

Hard to troubleshoot this stuff over the internet. There's obviously something wrong, and a good tech can track it down pretty quick. I'd also not rule out the radio. The XTL line is getting old enough to vote, and if it hasn't had a visit to a shop for a trip on the service monitor, then it should. Public safety should not rely on a radio that old with a compromise antenna installation.

 

[Jfox642]

Mounting any antenna on the headache rack is likely to be an issue. While the antenna does not -require- a ground plane, it will work better with one. Having the antenna mounted there is going to give it a very lopsided ground plane and thus a lopsided radiation pattern.

I would not trust "Pre-tuned". Tuning will change slightly depending on how/where it is mounted. SWR being a bit high isn't going to be a huge problem and probably not the cause of your issue.

The glass mount working 30 miles on your wife's car means that the repeater is probably OK and your wifes setup is good.

I would start looking at your entire installation carefully:
-Make sure radio power is getting good clean 12 volts.
-Positive power lead needs to go directly to the positive terminal on the battery with a fuse installed as close to the battery as you can reasonably get it. Any other power source (cigarette lighter, tapped fuse, etc) is all going to give you problems.
-Negative lead should be grounded to the vehicle chassis close to the radio. Don't run it all the way back to the battery, as that will bypass the sensor on the negative lead and will confuse the power management in the newer trucks. It also gives you a good local ground.
-I would really, strongly, suggest having the antenna permanently installed dead center of the cab roof. This will give you a proper ground plane, proper ground connection, and much better performance.
-Running coax through doors/windows, or however you got from the cab to the headache rack might be an issue. Cable getting pinched/damaged will cause problems.

Hard to troubleshoot this stuff over the internet. There's obviously something wrong, and a good tech can track it down pretty quick. I'd also not rule out the radio. The XTL line is getting old enough to vote, and if it hasn't had a visit to a shop for a trip on the service monitor, then it should. Public safety should not rely on a radio that old with a compromise antenna installation.

I plan on going to mobilecomm Monday and having a tech look it over. Everything was installed by our county guy that does most the installs here. So I would assume all is good with that part of it. But doesn’t mean something isn’t wrong. My last resort was putting a hole in my roof, but if that becomes the issue I guess I’ll have to do that. Either way I appreciate the input! And I agree on the age of the radio, but we buy what we can afford unfortunately.

 

[ramal121]

My nemesis these days for VHF are car chargers. Anything plugged into a power port or USB port to charge up can possibly throw out so much static and noise from its power supply that your receive is completely wrecked. Easy enough to pull plugs or fuses and look for an improvement.

If you go by the shop the tech can test for this with a service monitor and if it is the case, how bad it is.

 

[ofd8001]

I'm sure this might be open to debate. . .

On my truck I use a trunk lip antenna mount on the hood. It's for an 800 digital TRS, so there isn't a tremendous RF power involved. Seems to work ok. I also use a vehicle specific fender mount antenna (opposite side) for my VHF radio, but it is more listening than transmitting.

 

[tvengr]

My last resort was putting a hole in my roof, but if that becomes the issue I guess I’ll have to do that.

A quarter wave VHF antenna in the center of your cab roof will give you good omnidirectional coverage and minimize overhead clearance problems.

 

[FKimble]

A 55 inch VHF antenna is most likely a 5/8s wave. I would suggest a 1/4 wave on the roof! The radiation pattern of the 5/8s may not be high enough to hit the repeater if its on high location or tower.

Frank

 

[Jfox642]

Help is requested with an issue using a Motorola xtl5000. It is installed in my 2015 Ram 1500. It is remote head, so radio is under my back seat and the head in my console. I use this for fire/ems on vhf.

The issue is, there is some major interference that totally cuts out my receive capabilities. But only when the truck is on. The County radio guy has looked at it and all grounding and power and coaix cable are tight and in good working order. He also put a few of those “clip on” interference reduction things in various places with no change or improvement.

I will also mention that I took the radio to a local and major well known Motorola dealer, mobilecomm in Cincinnati and had the radio tested and tuned. So radio is solid as well.

I have attached a video for your viewing pleasure of the issue. Any and all suggestions and help is much appreciated!

Disregard that. Apparently I cat upload a video. If you would like to see/hear the video, let me know and I’ll figure out a way to send it somehow. Thanks again!

 

[AK9R]

Do you have anything plugged into the cigarette lighter sockets? Cell phone charger, for example? I have found that some of them generate a lot RF hash on VHF.

Any other non-OEM electrical accessories?

 

[K6GBW]

Antennas on headache racks often have problems with a bad ground. Putting the antenna..pretty much anywhere else is better. The idea presented above of a 1/4 wave on the roof is excellent. Also, 5/8 wave antennas produce a lot of gain and that might be causing a problem. Sometimes, less gain is actually better if your radio site is at a higher altitude. Does your truck have LED lighting? They can cause noise issues. Finally, have you checked the coax for continuity? It may be something as simple as a bad coax or a faulty antenna coil. Simple way to figure that out is to put a magmount VHF quarter wave on the truck and drive around to test it. If the magmount antenna works then you know you have a problem with the 5/8 wave. The comms guy that installed it probably has one laying around and he can loan it to you for the test.

 

[FKimble]

"But only when the truck is on"
Let's clarify "on": do you mean cranked up and engine running or just turning ign switch to on to provide power to electrical items??

Had to re-read the thread a couple times before I noticed this little tidbit in one of your last replies. Sounds like something in the truck ignition, fuel delivery or charging system is most likely generating the noise/interference that is causing your problem. If you have any led lights that could also be the problem. Anything else in your truck that uses 12vDC that did not come factory installed??????????

Frank

 

[madrabbitt]

Simple way to figure that out is to put a magmount VHF quarter wave on the truck and drive around to test it.

This is exactly what i was going to suggest.
This immediately rules out issues with your existing coax, antenna and antenna ground.

If this solves your issue, its time to re-examine your antenna. If it doesnt solve the issue you can lead towards the radio or outside interference. And if it was me, radio would be the last thing to look at.