Interference with MotoTrbo on MTR3000 VHF

[cgaines78]

I have exceeded my knowledge level. My FD runs a VHF MTR3000 in Trbo mode and we are having problems.

We changed to Trbo then soon after replaced heliax and antenna due to water tower sandblast an repaint and a 25+ year old antenna. We cover a city of 4 Sq miles and have been having connection issues with our handhelds. Our Police Dept and various volunteer FDs around us cover large areas using Trbo repeaters with no issues at all! We try to key up repeater an either get the ”Bonk” of no connect or it chirps like connected but audio doesn’t go out to any other radio. We can then key up again an it work fine Sometimes. This is not just in certain areas of the city but randomly in time and place But only on handhelds. (XPR3500 & 7550s) Our dealer came and checked the repeater inside an out and all was well, transmit power, receiver and reflected power all well in limits.

I am at my wits end. We installed Motorola’s TrboWatch server software on their 9 day trial an see numerous instances of interference almost like when repeater sits an keys up after a time the second leg of traffic shows interference just before the key up. See attached pic or PDF. This does not show up in our PDs repeater which is a newer version Motorola Trbo repeater but at same site as ours.

I’m truly pulling out my little remaining hair and have a bunch of upset firefighter cause they can’t trust their handhelds to work and a Chief wanting to know what we need to do to fix it!


Any and all help is appreciated.



Sincerely,

Chris Gaines
cgaines78@yahoo.com
Malvern FD
Malvern,Arkansas

 

[RFI-EMI-GUY]

Has anyone tested the repeater for desense , transmitter noise, receiver degradation (TNRD) and effective sensitivity?

 

[12dbsinad]

Clearly your dealer isn't sending true radio techs. There could be nothing wrong with the equipment itself, could be external interference. It's VHF, so that's very easly possible. They should be able to figure it out. Try another dealer.

 

[RFI-EMI-GUY]

Yes, someone needs to at least put an ear to the repeater input frequency. Sounds like all they did was a "bench check".

VHF has no set of rules regarding repeater pairing for Part 90. The FCC and industry IDIOTS clearly lost an opportunity to fix the VHF band during the narrowbanding mandate.

Another thing to check is that the handhelds might be set to inhibit TX if there is an on channel interferer on the repeater output channel. That might explain the BONKS.

 

[TampaTyron]

Another thing is to check the repeater programming, specifically the channel RSSI threshold. If it is set to anything weaker than -80 (like -90 or -100), the repeater may be disabling itself due to rf noise (real or imagined). Additionally,the handhelds may be programmed for what is called Channel Free with a -124 threshold. This would result in similar behavior where the radio will not key up because it believes there are other users on the channel already. Change this setting to Polite to Own Color Code (or similar,not Channel Free and Not Always). If these fail, you likely have an RF plumbing issue duplexer, jumpers, coax, antenna). TT

 

[cgaines78]

@RFI-EMI-GUY - I don't know what all tests he did but it did appear like a "bench test" as someone stated.

@TampaTyron The RSSI Threshold is set to -100. Do I need to change this and if so what to? I need to study more on RSSI.
The handhelds are set to Always I think but I get a beep when it thinks channel is busy vs a solid tone when it can't hit repeater and like I said sometimes it chirps fine like it went through but no audio goes to other radios.

Our PD has an old 8550 I think that I'm gonna program to our stuff and try out so that will prove it is the repeater somehow.

Thanks for all the help.

 

[TampaTyron]

Change repeater to -50 for testing. I typically set it around -80 for production. Make sure radios are set to polite or always (but the fact that you are getting a bonk when the repeater does not answer the subscriber indicates RF issue like improper RSSI threshold, high rf site noise, mis-tuned duplexer, RF interf, etc). TT

 

[MTS2000des]

@RFI-EMI-GUY - I don't know what all tests he did but it did appear like a "bench test" as someone stated.

any repeater and filter (duplexer, combiner, multicoupler, etc) needs to be vetted ON SITE. If this wasn't done, the "bench test" is the equivalent of pissing into a fan.
The site itself needs to be checked with a spectrum analyzer through the antenna to check the noise floor once the filtering is ruled out and proper TX/RX isolation is verified.
Not trying to sound harsh, but if the local shop is just throwing the repeater in a rack and connecting cables without doing any performance testing, their incompetent.

This is why duplexed systems need to be planned, tested and optimized by qualified persons. Good luck.

 

[N1GTL]

I have run into these issues. Plug a usb a-to-b into the repeater and look at the noise floor. I have seen noise floors at -95 forcing me to set the repeater to -92 or so just so subscribers can get in. As a side note, any "duplexer" that is pass-only without reject tuning is junk. Make sure you have a READ PASS-REJECT duplexer.

 

[cgaines78]

@N1GTL - I have cable and CPS how do I see Noise Floor? I have small rack mount duplexers but unsure if they are READ PASS-REJECT and unsure how to tell.

As you can tell most of my experience is just programming subscriber units for mine and other fire departments in the area.

 

[TampaTyron]

Use RDAC program and click Read RSSI. You will want to keep clicking it many times and keeping an idea of the noise floor where there is no one talking on either slot.

Once that is done, do the same thing but instead have a user key up a specific slot, preferably a good distance from the RF site. When the repeater keys up, did the RSSI noise floor go up on the unoccupied slot?

TT

 

[N1GTL]

If they are the small duplexers chances are you are dealing with notch only. True duplexers are pass and notch and to tune them right you need a return loss bridge. If you get one of those tuned right, you're looking at 105 db isolation or more.

 

[cgaines78]

@N1GTL - I have a full size set of cans from the previous repeater. Would it help to use those instead of the small ones??

 

[RadioGuy7268]

Why was the old "Full size set of cans" changed out? Did you change frequencies? What was the spec of the new Duplexer vs. the old one? Generally speaking, bigger is better when it comes to VHF.

Do you have the ability to tune or check the tuning of a can? It would be a pretty easy check to do a back to back test with the old vs. the new duplexer if the frequencies you're using are still the same. Make sure the jumper cables are good.

 

[cgaines78]

@RadioGuy7268 - We just got a new set with the new repeater when we narrow banded. Kept old set and old repeater though the repeater would only be good for HAM now I guess.

 

[celltech25]

My suggestion instead of getting on a Forum and searching for the Golden Spoon Fix get a qualified Radio Tech to come look at it

 

[MTS2000des]

My suggestion instead of getting on a Forum and searching for the Golden Spoon Fix get a qualified Radio Tech to come look at it

This is really sound advice.

Not to belittle the O/P, but there is a huge difference in skill sets and needed equipment used in programming subscriber radios and implementing and optimizing infrastructure.

As this system is a public safety radio system and not a ham or GMRS repeater, it really is best practice to get a qualified person(s) involved to do a baseline and come up with a plan to get reliable system performance in place.

 

[cgaines78]

@celltech25 & @MTS2000des - Thanks for the advice, I thought I already had a qualified Radio Tech come out but apparently all he did was a bench test. I have someone else coming next week with a device to check the heliax and antenna and replace a bad connection on another heliax in the same building. I was hoping I wasn't the first to have this issue and someone would have already figured it out but apparently I'm the first. I've told my radio shop either get it fixed or we will be forced to use another vendor from further away because this is a major safety issue now. We have implemented procedures to automatically goto our TAC channel (Simpex) on any working fire so interior crews will always be able to communicate to I/C.

I do have a XPR 8300 that PD isn't using anymore since they upgraded to do AVL through system. I'm thinking of programming it and hooking to our old cans and see if that fixes issue. Problem is it so random I just have to let it run till we get a long call with lots of radio traffic.


Thanks Again,
Chris

 

[celltech25]

@celltech25 & @MTS2000des - Thanks for the advice, I thought I already had a qualified Radio Tech come out but apparently all he did was a bench test. I have someone else coming next week with a device to check the heliax and antenna and replace a bad connection on another heliax in the same building. I was hoping I wasn't the first to have this issue and someone would have already figured it out but apparently I'm the first. I've told my radio shop either get it fixed or we will be forced to use another vendor from further away because this is a major safety issue now. We have implemented procedures to automatically goto our TAC channel (Simpex) on any working fire so interior crews will always be able to communicate to I/C.

I do have a XPR 8300 that PD isn't using anymore since they upgraded to do AVL through system. I'm thinking of programming it and hooking to our old cans and see if that fixes issue. Problem is it so random I just have to let it run till we get a long call with lots of radio traffic.


Thanks Again,
Chris

Yeah, I would start with putting the Repeater in Analog mode and testing the Duplexer/Repeater Combo and Cabling for Decense, then sweep the antenna line and antenna system, Check RSSI, Power out Reflected and go from there.

Also we put a system in a couple years ago TRBO Cap+ for a local power company worked great the first day, then day 2 it went to crap, went back out and found that the Transformer that fed the buidling next door to the tower was bad and throwing trash all over the place and causing the rptrs to shut down unless the RSSI was setto -40

 

[cgaines78]

Yeah, I would start with putting the Repeater in Analog mode and testing the Duplexer/Repeater Combo and Cabling for Decense, then sweep the antenna line and antenna system, Check RSSI, Power out Reflected and go from there.

Also we put a system in a couple years ago TRBO Cap+ for a local power company worked great the first day, then day 2 it went to crap, went back out and found that the Transformer that fed the buidling next door to the tower was bad and throwing trash all over the place and causing the rptrs to shut down unless the RSSI was setto -40

Thanks @celltech25, The "tech" had to program in analog to connect to a box for some test, also power out is 90 Watts and reflected was good at ~300 MiliWatts. I'm going tomorrow with laptop and RDAC to check RSSI and have tower people coming to sweep the heliax and antenna next week.

Thanks Again. I'll figure it out or it will all be replaced, that's my Chief's attitude now.