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Adjacent PL Tones on same frequency?



Recently I had an issue with another repeater using the same pair as mine. This repeater was unknown to anyone in our area (not listed here or on Repeaterbook). Another operator was located between my site and the other site, and he could communicate clearly with me and the other repeater owner. I could only catch part of the distant repeater output. The distant machine was using 136.5 and I use 141.3. Is the fact that these PL Tones are so close to each other explain why each repeater was receiving the other's output (at low levels)?

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I'd be looking at the equipment used also - on both sides, in addition to a full Preventive Maintenance check as suggested above - on both systems. PL tones that are "drifting" (not holding steady to the actual tone frequency) can cause what you're describing. 


There's alignment that needs to take place between the transmitters and the receivers - ie: a transmitter that isn't steady is going to have trouble with talking into a repeater receiver that is too "tight" and doesn't allow for any leeway to either side of the desired tone.  A receiver that is too loose is going to have the trouble you're describing - it's going to open up even when the actual PL is outside the normal "window" of desired operation.


If you want to get deep into the Tone PL theory - Repeater-builder has a bunch of good write-ups on PL and DPL/DCS : http://www.repeater-builder.com/tech-info/ctcss/ctcss-overview.html


The good news is, most of this was all worked out 40+ years ago, and if you're using quality equipment, it's mostly built-in. Zetron has a pretty good write up of all the details for "tuning" for proper PL decoding in the back of their Model 38 manual - copies of that manual are available online. The only times I ever spent time tuning for PL was when I was using an External Tone Panel to decode user tones.

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