PL Tones on CM300 Radios

[JimNorth]

Recently we have started to use cm300 vhf radios in our rental fleet. We have set them up with PL tones to utilize the frequency to its fullest. The radios have started to come back with the RX always breaking squelch - have taken off the tone and checked the squelch stteing this is fine(-120dBm) as soon as I put a PL tone on the channels with it the radio starts breaking squelch at -130 dBm. The channel will always be on if I put 8oo hz PL tone even at -130 dBm. Should i put the PL tone down to 500 hz then it still breaks at approx. -125 dBm. It will only break squelch properly at -120dBm when the PL tone is down to about 200-300 hz. Anyone have any ideas didn't want to mess with the RSSI settings as I don't know if it would correct it or not. Maybe the front end is just not of a good enough quality to support different PL tones on the same frequency, as these are notr a top of the line Motorola radio. Anyone have any ideas I would appreciate it.

Cheers;
Jim

[Al]

I guess I'm unclear on several points in your post:
1. The highest EIA PL frequency is 259.1 Hz, so I don't know how or why you're trying to use 500 and 800 Hz frequencies - they don't even fall within the bandwidth of the lowpass filters in the CM300 used for tone coded squelch, so there's no way they're going to pass a 5 or 800 Hz tone to the tone decoding input of the uP in the radio.
2. Two things to check if you agree that tones between 67.0 Hz and 259.1 Hz are needed to use the TPL squelch feature of the CM300:
a. TPL is only active when the hook input pin on the radio's mic connector is at low level, i.e. when the two hook contacts on the back of the mic are connected - or in other words, when the mic is on hook.
b. In the CPS, be sure the box labelled "off hook PL override" or some similar phrase is unchecked under the "general" tab.

[wavetar]

With the "expert" settings enabled, make sure to change the default 'Unmute/Mute Rule' from "Std Unmuting/Std Muting" to "And Unmuting/Or Muting". That should bring the squelch back down to -120 or so.

Todd

[jackhackett]

I believe when he says he's putting the PL at 500 or 800 Hz he means the deviation, not frequency.

[Bat2way]

Maybe the front end is just not of a good enough quality to support different PL tones on the same frequency, as these are notr a top of the line Motorola radio. Anyone have any ideas I would appreciate it.
Cheers;
Jim

Your quote doesn't make sense to a technician. Sounds like you have something amiss in your programming as we have had absolutely ZERO problems with this unit using PL or DPL. Do you know computers and VHF radio receivers don't get along at times due to the computer RF spray interfering with the IF freqs and the radio TX messing up monitors?

You can just program the check box to mute the radio to only open with PL. Also have never had a problem with the squelch being programmed to "Std Unmuting/Std Muting". Please advise what you find out.

[wavetar]

You can just program the check box to mute the radio to only open with PL. Also have never had a problem with the squelch being programmed to "Std Unmuting/Std Muting". Please advise what you find out.

You may not have run into a problem, but we have. Both the commercial & professional series using the "std" setting we found to be far too sensitive to use in close proximity to another radio on a channel within 200KHz or so with the same PL...they would unmute for the co-channel interference. Testing with a monitor showed exactly what Jim described...you couldn't make the radio mute going down to -130. Changing it to the "and/or" setting solved all the issues.

Todd

[JimNorth]

Thanks to Todd for the fix. Changing the setting from "std" to "and" did indeed fix the problem. Also sorry for not being more precise in my question I thought it would be taken for granted that I was talking deviation of the PL tones when I said 800hz 500hz etc. Also just because a fault has not been seen does not mean it dosen't exist. Nuff said.
Cheers;
Jimnorth

[wavetar]

Happy to see it worked for you. Thanks for reporting back.

Todd