[aprssig] ***SPAM*** Re: APRS freq spec questions

Stephen H. Smith wa8lmf2 at aol.com
Sun Mar 29 01:53:44 EDT 2015

On 3/28/2015 11:16 PM, Kenneth Finnegan wrote:
> To answer one of my own questions on this, testing the T vs C access
> commands with K4JH on his THD72a, it appears that I guessed correctly.
> T100 will configure your radio to only encode a PL of 100Hz, where
> C100 configures your radio to both encode and decode 100Hz. I would be
> interested in seeing how radios respond to both at once ("T100 C127").

"T" refers to "Transmit".    "C" refers to "CTCSS" (Continuous Tone Coded 
Subaudible Squelch) a.k.a. "PL" (Private Line) which is a Motorola Trademark.

Note the word "SQUELCH" in CTCSS; i.e. focusing on guarding the receiver, 
rather than encoding a tone on the transmitter side.  In practice the "CTCSS" 
setting normally enables tone coding on both receiver AND transmit.

In ham usage, it is most common to use tone on the transmit side only (to 
activate a given repeater), but have the users' receivers running on carrier 
squelch only on the repeater's output channel.

In commercial land-mobile use, it is far more common to tone-squelch the users' 
receivers since most land-mobile frequencies will have multiple unrelated 
businesses or government agencies sharing the RF channel, that don't want to 
hear each other.

In ham use, tone-squelching the user's receiver is most often done by related 
family members (husband/wife pairs, etc) that are both hams, so that one 
partner only interested in the other doesn't have to listen to all the other 
chatter on the local repeater.

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