[FedCom] Re: Unknown Frequencies (J Doe) - Is that your real name?

[tvsjr]

> repeaters
> are opened with a brief preamble ( the short "chirp-chirp" sound before
> the
> encrypted voice). The preamble is accompanied by the correct PL tone, so

The chirp-chirp you hear is an MDC1200 ID and is not an inherent component
of Securenet. Two different technologies.

Quants can be configured to only repeat traffic having certain MDC pre-IDs,
but this is not a requirement.

The chirp-chirp is not heard on ASTRO traffic because the IDing is imbedded
into the datastream.

> the
> repeater opens and stays open for the length of the transmission.

The repeater stays hot because it's a Motorola Quantar which understands
Securenet. A Quant is not a simple passive repeater - it actually
understands the data being sent to it (Securenet, ASTRO in later firmware
revs) and munches on that data on the way through. Thus, it knows when the
incoming signal is a digital flavor to be repeated and does so.

> NAC's are used with the P-25 transmission modes.

Correct. The NAC is a twelve-bit value in the range 0x000h to 0xFFFh.
Certain NACs have special meanings (0xF7Eh for "CSQ", 0x293h being the APCO
25 interop standard), but, in general, pretty much all are available for
use.

> So it is possible to use CTCSS tones with a DES encrypted transmission,
> but
> your repeater has to be able to deal with it...

Wrong. 12K CVSD Securenet is already pushing the 5KHz channel to its limits
as far as information capacity is concerned. Chopping off the bottom 300Hz
for PL/DPL to pass means there's not enough bandwidth left to pass the
digital data through.

This is also while you'll see a PL decoder false occasionally when looking
at a DES transmission.