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  Digital Selective Calling (DSC) VHF

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Author Topic:   Digital Selective Calling (DSC) VHF
triblet posted 05-21-2001 09:03 PM ET (US)   Profile for triblet   Send Email to triblet  
I finally got a chance to play with the
DSC on my Standard Horizon Spectrum at the
SF Rendezvous this weekend. I like it.

DSC allows two VHF radios to communicate
digitally. All new VHF console-mount radio
designs have to be DSC-capable, and most of
the $180 and up units are already. Over time,
the cheaper units and the handhelds will also
become DSC capable. You have to register
your boat at http://www.boatus.com/mmsi/
(it's free) to get your MMSI(Marine Mobile
Service Identity). This is your boat's
nine-digit "telephone number".

The most important function of DSC is a
one-button digital MAYDAY (we didn't try
that). The Coasties aren't, in general,
setup for it yet, but it's coming soon. And
any DSC radio with in range copy the Mayday.
If you GPS is wired to your radio, the
digital Mayday will include your position.

You can also use DSC to call your buddies. You
set the working channel, push a couple of
buttons, and the other radio rings and is set
to the right working channel. You both just
key the mike and start talking when it rings.
Hoop and I used this to good advantage on
several occasions at the rendezvous.

Chuck

Hoop posted 05-21-2001 11:40 PM ET (US)     Profile for Hoop  Send Email to Hoop     
Yup. DSC works pretty well. It's like ringing someone up on the telephone; only they know that you are calling, although everyone would of course hear your conversation on VHF.

I did find that, with today's technology, the access of the DSC feature has a ways to go. Entry of the MMSI numbers isn't that convenient; you couldn't very easily do it on the fly. Scrolling through screens to use the feature was easier, though not where it might be in the future. You almost need a bigger VHF screen.

Still, when you're dialed in, its great to know that the person you are calling with DSC will absolutely know that you are calling. The "ringing" sound is quite distinctive, and most definitely insistent!

Hoop

jimh posted 05-22-2001 12:37 AM ET (US)     Profile for jimh  Send Email to jimh     
I haven't made a thorough study of DSC yet, but I was under the impression that the tranmission was not altered, that is, it is not "digital", but rather the receiver squelch circuit is changed so that it only responds to transmissions which are coded with the proper digital identification.

The radio still transmits in 15F3 frequency modulation, but with a digital number encoded in the modulation, right?

triblet posted 05-22-2001 10:13 AM ET (US)     Profile for triblet  Send Email to triblet     
No, I don't think it's squelch coded like
the FRS radios.

There's definately a modem that modulates the
digital messaging on Ch 70 to get the initial
connection dialed up. After that, it's just
VHF-FM voice comms on the selected working
frequency.

Chuck

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