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Low Frequency Paging Tones and PL Interference?

This forum is focused on discussing Digital and Voice paging equipment, protocol's, infrastructure, and Motorola specific hardware used. Please refrain from discussing different ways to monitor the digital paging systems due to the legalities of such.

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Birken Vogt
Posts: 262
Joined: Thu Nov 10, 2005 7:53 pm

Low Frequency Paging Tones and PL Interference?

Postby Birken Vogt » Tue Dec 01, 2015 6:16 pm

Newish customer. Got a complaint that one department with a ~330 Hz B tone is not decoding reliably. PL tone is ~131 on this setup. They may have been running no output PL on the repeater in the past. Levels and waveforms have been checked and rechecked.

One theory that has been postulated is that the paging tone being so low is almost similar to a PL tone and they are not playing well together. Is this a valid idea?

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Joined: Tue Sep 04, 2001 4:00 pm

Re: Low Frequency Paging Tones and PL Interference?

Postby Al » Tue Dec 01, 2015 8:21 pm

If the repeater's PL deviation is correct assuming 12.5 Khz operation, the B paging tone should be a lot higher in level than the PL. Only reason that I can think of for any problems would be a nonlinearity in the audio portion of the repeater that might generate audio intermods. Then the audio limiter or IDC in the repeater would reduce the overall deviation to 2.2-2.4 Khz. Have you tried looking at the flat output of a test receiver with an audio spectrum analyzer to see if the PL and the B tone are clean and at about the right relative levels?

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Re: Low Frequency Paging Tones and PL Interference?

Postby RFguy » Wed Dec 02, 2015 6:36 am

As Al suggested, look for distorted tones. It's common with low frequency tones. We run PL on paging all the time, no problem, but low tones can be an issue if levels are not correct and tones are distorted. Good suggestion to scope the discriminator (flat audio) to see the quality of the tones.

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