MT2000 UHF PL/CTCSS Deviation

[kb5udf]

Hi all,

I have a UHF MT2000 in amateur and GMRS service. Friends have advised (and I confirmed) that when transmitting a PL, I have some type of humming noise, low and in the background on my audio. One of the friends works in commercial radio, and said it sounds like my PL deviation is too high. The noise is not overly strong, and doesn't interfere with communication but it is present when transmitting a PL, but not present without.

I read a service manual indicating the PL deviation should be >500 and <1000. Where/how do I adjust this? My plan is to just gradually reduce until the offending
noise goes away.

Thanks

JB

 

[Ubbe]

Could it be that you normally do not make use of the PL feature and you have your set to a high frequency like 250Hz, that will bleed thru in the audio filters of most receivers, and others use a lower tone like 100Hz that receivers filter out with ease? Maybe it is the TX modulator that have some distorsion at low audio frequencies and it needs to be tuned to produce a cleaner sinus wave?

As far as I remember the PL modulation level are fixed and cannot be changed using normal service software.

/Ubbe

 

[RBMTS]

Deviation alignment can be accomplished in the service setting of your RSS programming software. However if you have never accessed it before, be very careful about what you modify. You can quickly make the radio unusable. You really should have a service monitor and frequency counter to see if the radio TX might be slightly off frequency or what the deviation is at or being changed to. If you belong to a radio club I'd suggest you ask other members if they know of a local person that can align Motorola MT radios.

 

[kb5udf]

Thanks guys but I've accessed service mode many times before. I am specifically looking for PL deviation, as referenced in the service manual, but I can't seem to find such a setting. I just keep seeing what looks like t/x deviation.

Thx Ubbe but its not an incorrect PL. I am familiar with the low hum bass that makes, and this is higher pitched, because people with small ht's can hear it.

 

[Ubbe]

I think low frequencies like PL tones are phase modulated and higher audio frequencies are FM modulated. There's some adjustments that can be done to get a cleaner PL modulation without any multiples in higher frequencies that you get if it's not a perfect sinusodial wave from the PL tone. It's probably extremly difficult to do anything, without the proper instrumentation, that wouldn't mess up the voice audio.

/Ubbe

 

[MTS2000des]

Transmit on a mode programmed for carrier squelch. If you still here a hum/warble, this is typical of some Jedi RF boards with VCOs coming out of lock and/or RF shielding issues. Remember these radios are 20 years old, hardware went through many revisions. The RF boards made in the mid 1990s (1994-1996) were the worst.

 

[kb5udf]

Transmit on a mode programmed for carrier squelch. If you still here a hum/warble, this is typical of some Jedi RF boards with VCOs coming out of lock and/or RF shielding issues. Remember these radios are 20 years old, hardware went through many revisions. The RF boards made in the mid 1990s (1994-1996) were the worst.

Thanks, that was the first test I tried; no noise present with TX CSQ. But yes, I do realize this is an antique

 

[cmdrwill]

So, radio needs alignment and calibration. And one needs a service monitor and scope to do the deviation align/cal.

We still work on these fine antique's.

 

[kb5udf]

I have access to all that. That question remains does anyone know where to access Pl deviation in the service menu if it exists as a separate setting?

 

[cmdrwill]

You should try to find the Service manual FIRST. Transmitter alignment. Deviation Compensation.