Lee Williams wrote: > > Please explain how the lack of a high pass filter in a ham grade rig > affects tone decoding on a repeater?
Sure, Lee. Commercial radios have high pass filters that make sure no CTCSS components from the voice make it through the transmitter. Of course, this is one reason why some hams think the commercial stuff sounds like crap - audio below 300 Hz or so is severely attenuated. This is done on purpose. Anyway, back on track. Since many ham rigs do not have high pass filters, CTCSS components from the user's voice DO make it through the transmitter, and can actually compete with the CTCSS encoder as the 'dominant' tone. This problem is much more pronounced when the repeater is CSQ, as there is no encoder on the user's TX and the repeater tone panel will accept 'any old tone' it sees on the voice as a valid CTCSS tone. Believe it or not, I've actually accessed repeaters by humming the right CTCSS tone. I could never master talking while humming, though. Note, this was using a ham rig, not a commercial radio. > Most ham grade radios dont have > high pass filters on their RECEIVERS,hence the annoying hum heard on > their speakers. Yep - also true on most scanners (recent offerings have been much better). I've often used the tone to identify who is talking. (decoding the CTCSS by ear) > The most common problem I see is that most ham grade > radios have their tone deviation set too high and some have crappy > looking waveforms full of harmonics which can drive these panels > crazy. That's another factor, but can (usually) be fixed. The missing high pass filter cannot. Of course, the reason they don't have them is cost. It's much cheaper to skip it and makes the radio sound more natural. Joe M. Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
