MTR2000 TX PL Problems

mark102 · Post by **mark102** » Mon Dec 06, 2004 9:16 am

We've installed 2 new MTR2000 UHF 100w repeaters and have had a couple of problems. One that has not been resolved is the apparent loss of TX PL during transmissions. This is intermittent and is only for a brief period. There is no break in TX or audio, but seems to be PL only. This causes an audio "hole". Listening with CSQ is OK, only with PL decode is there a problem. Anyone have a similar problem ???

RKG · Post by **RKG** » Mon Dec 06, 2004 2:18 pm

Check the PL tone deviation level. Should be on the order of 750 Hz for a 25 kHz channel. However, it is often quite a bit lower, which will work most of the time, but if it is at the low end, the tone can be masked by the deviation of the voice signal.

Post by **wavetar** » Mon Dec 06, 2004 2:29 pm

Are you getting the same problem on both repeaters? Weird if you are. Are they set for CSQ & are simply passing the PL tone through, or are they programmed to decode the tone, strip it, then encode onto the tx audio? Have you verified tone level with a service monitor, have you seen the tone disappear on a service monitor as well? Have you tried a different PL or DPL to see if it acts any differently?

Todd

mark102 · Post by **mark102** » Fri Apr 15, 2005 5:42 am

OK. After much delay, Motorola said to turn off "Analog Boost" to see if this helps. Also, the squelch was 100 out of 127. Reset this to 25. All else checks OK with PL decode & encode and deviation. We've found this problem to be with all 4 of our MTR2000s not just the 2 new ones but 2 that are about 2 years old as well. Going to try this for a few days to see what happens. If no better, we will change the drop out to 1 second and try that.

Post by **wavetar** » Wed Apr 20, 2005 1:49 pm

The only time we have had to disable analog boost was when using the repeaters in trunked configuration with MTX850 portable field radios. In our case, the RX audio in the portables was driven to the point of distortion with it enabled. I have never seen it make any difference with PL encode. Mind you, I've never seen the PL drop out for any reason, other than using the Aux TX input on the rear of the MTR2000.

The squelch setting at 100 is factory standard (don't ask me why). I have found setting it any lower than about 35-40 causes the receiver to always be unsquelched. This will cause you to activate the TX soley on PL/DPL (since carrier is always activated)...which may or may not work out for you. To set it for exactly 0.25uV (-119 dBm), a setting of 45-50 is usually what works.

Todd

Dan562 · Post by **Dan562** » Wed Apr 20, 2005 7:51 pm

Two questions:

What type of Subscriber units are you using in your system?

What are the Dispatchers, mostly Male or Female voices?

Dan

mark102 · Post by **mark102** » Thu Apr 21, 2005 4:57 am

The PL dropping out only seemed to occur with mobile and portable units which are CDM1550s and MT2000s. Turning off analog boost has cured the problem of the PL dropping out but we are still having problems with portables getting into the repeater. It's as if the sensitivity is not good. It checks OK, however. No problems with the old MSR2000s and the antennas & transmission lines check good. The PL drop outs occurred with mobiles and portables with both male and female voices. Also didn't matter if the signal strength was good or poor. I almost would like to have my MSR2000s back. They worked for 20 years with little problem.

Post by **xmo** » Thu Apr 21, 2005 5:33 am

Perhaps there is a source of noise near your site that is impairing your receivers. You should rule this out by having your effective sensitivity tested.

Here is one write-up on how to do it:

http://www.repeater-builder.com/tech-in ... esens.html

Dan562 · Post by **Dan562** » Thu Apr 21, 2005 2:36 pm

Lets assume you ordered the MTR2000 from the /\/\ factory.

Did you order the X265 High Performance Preselector Option with the Base Station?

Did you order the X182 Standard 6 Cavity Duplexer Option included and tuned at the /\/\ factory?

On the Mobile Subscriber units being CDM1550s, which RF Power Output Level are these units capable of, 25 or 40 Watts?

On the MT2000 Portable Subscriber units, they have the Low 1 W or High 4 W RF Power Output selection. How do your users have the RF Power level selected?

Post by **wavetar** » Fri Apr 22, 2005 5:00 am

I'd like to see a copy of one of your codeplugs, for curiosity's sake. I have replaced many MSR2000 with MTR2000, and in my experience the MTR blows them away coverage-wise, especially in UHF. Are the frequencies for the MTRs the same as the old MSRs?

Todd

mark102 · Post by **mark102** » Mon Apr 25, 2005 9:20 am

The mobiles are CDM1550s @ 40w, portables are MT2000s @ 4w. Freqs & tones are the same as the old MSR2000s. Antennas & feedline check OK. A temp repeater was put into service with no problems. We have 2 older MTR2000s, about 1 year older, that exhibit the same problems. No receiver desense found. Repeaters are actually at 3 different sites. One site has no other equipment. The repeater was ordered as follows:

T5544 MTR2000 Analog Repeater
X540 100 Watt UHF w/Internal Circulator
X597 Conventional Analog Operation
X580 Repeater Operation
X265 Narrow Preselector
X182 Duplexer
X84 Omit Wireline Control
X52 30 inch Indoor Cabinet
X121 DC Only Operation
DQLSRM25BB 28v 25A Power Supply

The older MTRs are 30w instead of 100w.

Post by **wavetar** » Tue Apr 26, 2005 12:07 pm

I notice the DC only option was ordered. What are you using to supply the 24vdc to the MTR's?

Todd

mark102 · Post by **mark102** » Tue Apr 26, 2005 1:10 pm

An Astron power supply with battery back-up. We have 8 more of these in 12v both on repeaters and control stations with no problems.

Dan562 · Post by **Dan562** » Tue Apr 26, 2005 7:31 pm

Hello Mark,

May I suggest as an experiment removing the Astron Power Supply completely out of the circuit so the MTR2000 is operating strictly off the batteries and nothing else. Then allow the repeater to operate as normal under this mode and see if the portable subscriber units transmit signals are able to access the repeater's receiver under this condition.

There's also one other item to consider between the 40 W mobiles and the 4 W portables and this is a minimum of 10 dBm signal difference between the two type of units.

You may want to review an earlier post by Wavetar using MCS2000 Control Bases and Astron Power Supplies .... it seems they are not everything they're touted to be.

Dan

Post by **wavetar** » Wed Apr 27, 2005 5:12 am

Dan562 wrote:
You may want to review an earlier post by Wavetar using MCS2000 Control Bases and Astron Power Supplies .... it seems they are not everything they're touted to be.

Dan

Yeah, those were the HPN4002 switching power supplies, made by Astron for Motorola. It sounds like he's using RS20A-BB or a similar linear power supply.

Mark, you didn't actually specify what the voltage of your power supply was. For a 100 watt MTR it needs to be 24/28 volts. I just wanted to make sure it wasn't as simple as the station only running on 12 volts or something. I'd check the voltage under load, as well, to make sure it isn't dropping & causing issues.

Todd

mark102 · Post by **mark102** » Wed Apr 27, 2005 5:43 am

The power supplies are Astron LSRM-25-M-BB. 25A 28v DC w/battery back-up. No problems with power supply output. As part of our looking into these problems, we've checked for spurs, receiver troubles, and any other problem we could think of that would cause the receiver to be poor. Nothing found so far. We are going back on Friday to look again. We've checked areas where there used to be no problems getting into the repeater with a portable and now we have trouble. I have wav files of some of the transmissions if anyone would like to listen to them.

mark102 · Post by **mark102** » Thu Apr 28, 2005 9:05 am

OK. We re-checked everything with one of the repeaters and found no apparent problems. RX checks excellent. No desense. RF noise level low. No spurs on TX. Squelch opens at about 7 or 8, reset to 15 & works good. We did reset the hang time from 0 to 1 second to see what that does. Also did checks with & without the power supply. All OK. Going to wait & see the results of this before reprogramming any of the others.

Thanks to everyone for their help.

Mark

mark102 · Post by **mark102** » Mon May 02, 2005 4:38 am

After the re-programming the repeater seems to be operating "better". Changing the drop-out time to 1 second has helped as weaker signals were causing the repeater to drop all the way out and then back up when set to 0. With 2 repeaters this is causing some other problems as some units are on different repeaters at times and talk before the repeater drops out.

The MTR has a "noise canceller" feature which enables the "flutter fighter". I've seen noise blankers on low band and a similar option for 900 MHz but not UHF. I've been told this might eliminate the pops and cracks from portables. Anyone have any experience with this on UHF ???

Thanks.