[FedCom] Fedcom DCS

Wed, 17 Dec 2003 04:21:03 -0500

If Ruff is using a BC250D(or 785/796) he should be able lockout an interfering
analog signal IF it has a subaudible tone on it. Cant say if this inlcude the
Mexican signals. Unfortunately none of the current crop of P25 scanners have
the ability to selectively monitor certain P25 sigs based on their NACs. I
suspect this ability as a feature may be some time in coming as many(most)(non
Fed) P25 systems currently in use are also trunked systems. However where I
live in NH, this is something of an issue as cept for one city w/ an 800 Moto
system, all of the P25 systems used by the State, Counties and several cities
are all conventional VHF systems.

Two possible solutions. One  is a simple mod we have come up w/ that prevents
the BC250, and likely 785/796(?) from unsquelching on anything but a valid P25
signal. The main drawback is that its an all(CH) or nothing. However you can
bypass it by whenever the P25 card is disabled. Another woudl be to get a
Motorola radio such as an XTS3000 and set the various freq/CH "personalities"
for (generic) "digital squelch". I cant recall the specific programming command
right now, but this will cause the radio to unmute only when it receives a
valid P25 signal, regardless of the NAC. However if you know the NAC for a
given dept/agency so much the better,,. Does anyone know of any NACs for
agencies using P25 currently??

Shameless plug: If you want a quick intro to P25 NACs, take a look at my column
in the Dec issue of Scanning USA.
Steve

Chris Parris wrote:

> >>>
> Does anyone know what DCS ( digital control squelch??) is being used on
> these new 100% digital channels that agencies like Customs, Border Patrol &
>
> FBI are using? Thanks / Ruff
> <<<
>
> Ruff,
>
> DCS (Digital coded squelch) is not used on the digital radio systems,
> despite the sound of it. DCS is used on analog radio systems in the same
> way that CTCSS, or subaudible tone squelch is used. Most newer scanners
> will do DCS as well as CTCSS tone squelch...
>
> The APCO digital systems utilize what is called a Network Access Code or
> NAC. That is a way to let only radios with the same NAC talk to each other.
> There is no consumer level radios that will do anything with the NAC yet.
> That may be an option at some time in the future, I suppose...
>
> As far was what Customs and Border Security units are using for their NAC,
> I have no clue.
>
> I am assuming that you wish to put in some sort of tone squelch to keep out
> the Mexican interference. I have not tried putting a tone squelch value in
> the BC-250D to see if the digital traffic will still come through or not.
> I'll experiment and see. I know that the PRO-96 will not allow you to have
> a tone or DCS squelch on a digital channel...
>
> - Chris
>
>  --
>  Chris Parris
>  Beaverton, OR
>  [email protected]
>  www.groups.yahoo.com/group/pdxmilcom
>  www.live365.com/stations/cparris2
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