> >Do you assume multiple frequency operation? > Yes. I never much cared to adapt the design to multi frequency aps but it was done. Most all the repeaters in our area use the same 127.3 ctcss tone. We did use a common 2 pole 6 position radio shack source rotary switch to select different adjustable pots (controls). It worked pretty well where needed.
> Well, I did in every case. Not surprising, as there's a lot of odd > harmonic content within a square wave; I suppose the lack of a > 2nd harmonic helps your LPF design a little. Plus if you're > feeding a phase modulator, you've got another 6 dB/octave working > against you. Perhaps you were feeding direct FM modulators & > using higher CTCSS freqs.? Just various older radios with the "modulator of the day" circuit. We used the lpf shown with some circuits by nature of their design also adding to the harmonic attenuation. > Perhaps it's a difference of perception. Back in the day, there > was a rather high emphasis (pun quasi-intended) on PL tone purity. You are right... I remember when I would have never thought to use a 555 as a tone generator. I have a number of pre-555 design, op amp ctcss circuits that never seemed to be really reliable... ie stable. Those darn feedback circuits with a mini light bulb installed. But the 555 circuit was/is always a winner... it works darn well for what it is. > If your encoder had any harmonic content others let you know. > In addition, some of the repeaters around here seemed to > 'emphasize' the PL harmonics for some reason, as they sounded > worse through the repeater than when heard directly. I would suspect the way both receiver ctcss & voice audio is or is not properly handled is the key. I seem to find a lot of repeaters don't remove or reduce the received ctcss before sending the audio along... Any heavy audio compression just seems to make the ignored ctcss blow-through and harmonic problems much worse. Less we also forget how most current Amateur Radios arrive with smokin' hot deviation. I'm often surprised some of the circuits I run into even work as well as they appear to... > Looking at the drift specs, it looks like all my drift problems > with the XR2206 were likely limited to the Rs & Cs used, as > even a 50 °C change would only result in a typical 0.1 Hz > drift @ 100.0 Hz (due only to the chip). > > Bob NO6B The Network RC Parts are most often the biggest sinner. Cheap caps and resistors keep the show moving along even if you don't want to travel that road. cheers Bob, s. ps: when we get done talking about the 555 ctcss encoder I've got a less popular 567 ctcss encoder/decoder circuit available.
