Re: [Hamlib-developer] Tone -vs- CTCSS

[Nate B. <n0...@ne...>]

* Dale E. Edmons <de...@w-...> [2002 Jul 06 21:24 -0500]:
> Chuck,
> 
> That sounds quite like actual operation.  I've only read
> bits and pieces.  After keying up a repeater and getting
> on the air I haven't spent much time on it.  It also explains
> why repeaters wouldn't key-up with CTCSS on.
> 
> However it works is fine.  As long as hamlib works as expected
> all is well.  I'll have to do more reading on this soon.

Perhaps I shall take a stab at this.

CTCSS, Continuous Tone Coded Squelch System, is the generic name for the
subaudible tone frequencies ( < 300 Hz) used to minimize co-channel
interference.  This system went under a number of trade names including
Motorola's Private Line (this is why you'll see CTCSS also referenced as
PL tones) and GE's Channel Guard.  Regardless of the name there are a
number of "standard" and a number more non-standard tone frequencies.

Normally, in a commercial setup, all the radios for a given group will
transmit (encode) the same tone and the associated receivers will
unsquelch only when an FM carrier with the proper tone is received
(decode).  To facilitate more than one group of users on a repeater,
each group will be assigned a CTCSS tone by the repeater operater and
the repeater will use a "shared tone panel" that is programmed to
respond to the various tones in use.  Each transceiver has a monitor
function so that when the microphone is removed from its hanger the
receiver now will operate in carrier squelch mode and receive everything
on frequency.  This is to prevent "doubling" or "talking over" another
station.

We hams tend to use CTCSS only for two reasons.  In the early days it
was a crude means to operating a "closed" repeater as few radios had
CTCSS capability and adding it was often expensive.  The most common
reason we use CTCSS is to avoid the repeater from keying up due to
receiver intermodulation products or from distant stations not intending
to use the local machine during band openings.

Most ham rigs support the following three states:

encode off, decode off
encode on, decode off
encode on, decode on

Encode always applies to the transmitter and decode to the receiver.

It appears from your note above the TS2K supports a fourth state, encode
off, decode on.  None of my Yaesu gear will do this and it seems to be
of dubious value to me, but whatever.

So now, following along with your threads, it appears there is a
seperate command to set the TS2K to encode "ON" or "OFF" and another to
set the decode in either state and both are independent of the other.

Keep in mind that "tone", "CTCSS", "Subaudible tone", "PL tone" are
references to the same thing, a steady tone modulated on the FM carrier
for the purpose of allowing a receiver expecting that tone to be present 
to unsquelch and receive your transmission.  Nothing more.

DCS, Digital Coded Squelch, is a variation on the same theme, however,
instead of a steady tone the FM carrier is modulated by a data stream.
The datastream contains a multidigit code programmed into the radio.
The system works the same way except many more codes are available, thus
a DCS system is harder to "crack".

"Tone burst" refers to the system in use in Europe when at the beginning
of a transmission a short 1750 Hz tone is transmitted and the repeater's
receiver will unsqelch and the repeater can be used.  This system is
seldom used in North America.

I hope this helps to clarify some of the terms and their operation.

With regard to Hamlib, it seems to me that the CTCSS routines in rig.c
ought just be mapped to the correct command codes in the ts2k backend to
enable/disable encode/decode.  Is it not this simple (I haven't read any
of the ts2k code)?

73, de Nate >>

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