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Author Topic: Hearing PL tones......but only on one linked system???  (Read 1129 times)

W5OT

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Hearing PL tones......but only on one linked system???
« on: January 14, 2019, 04:28:29 PM »

My ARC has a couple of 2 meter repeaters linked with a couple of 440 repeaters in town.  When I check into the weekly net on sunday nights, I can hear the PL tone in the background on my Icom 746 Pro.  Doesn't matter which 2 meter repeater I'm on, I hear it on both.  I've searched the forums and the only other references to this issue seem to point to a radio that doesn't filter the tones out very well.

I'd think this would be my issue IF I heard it on ANY of the other linked repeater networks in town............but I don't.  I don't hear any background tones on ANY OTHER 2M REPEATER.......and there are over a dozen.

Should I say something to the repeater coordinator at the next club meeting or am I making something out of nothing??
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K5LXP

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RE: Hearing PL tones......but only on one linked system???
« Reply #1 on: January 15, 2019, 04:15:47 AM »


First thing I'd try is to hook the radio up to a scope or audio analyzer software on a PC and see if it's really a PL tone (i.e. the expected PL tone frequency) and also to see if it's sinusoidal.  What I've encountered in the past is sometimes it's either just 60Hz buzz that gets through a link or coupled somewhere into the controller audio or if it's PL, it's overdriven somewhere and what you're hearing are the harmonics of the tone.  You can make sure the 746 isn't adding it's own distortion by transmitting on frequency with a tone from a local radio or signal generator then comparing that to what you're monitoring over the air.

Mark K5LXP
Albuquerque, NM
 
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WB8VLC

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RE: Hearing PL tones......but only on one linked system???
« Reply #2 on: January 15, 2019, 08:40:16 AM »

Does that model have flat, dc to 3 KHz, receive audio frequency response in FM?

A quick test is to just turn the receive TONE SQUELCH on and select the proper receive ctcss tone?

That should strip away anything below 300hz on receive.
« Last Edit: January 15, 2019, 08:43:02 AM by WB8VLC »
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KD4UPL

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RE: Hearing PL tones......but only on one linked system???
« Reply #3 on: January 19, 2019, 06:14:07 PM »

What is the frequency of the PL those repeaters use? The higher frequencies, like up in the 200 Hz range, are a lot closer to the audio pass band of your radio than the lower tones (like down around 70 Hz). It may just be that your radio passes really low frequencies. Do you have a DSP or something you could adjust?
Or, it could be those repeaters are transmitting tones "louder" than other repeaters.
I guess you could say something to the control ops about. Approach it as a question and a learning opportunity. Don't come across like there's something wrong with their repeater and they need to fix it for you. Remember, they are just fellow hams providing a repeater for others to use out of the kindness of their hearts. Repeater ownership is time consuming and expensive.
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