N00b to Astro and digital in general..

poser · Post by **poser** » Thu Jan 26, 2006 9:27 pm

What exactly does digital offer? (D Star, APCO 25 and Astro?) Sorry, I don't even know enough to ask about the options. Thanks

515 · Post by **515** » Fri Jan 27, 2006 7:39 am

For APCO Project 25 digital conventional, on properly programmed/flashed radios:

Unit ID transmission/display that works much better than any MDC1200 or DTMF pre/post scheme.

Unit-to-unit (selective calling) that works much better than any MDC1200 or DTMF scheme.

Emergency alert that works much better than any MDC1200/DTMF scheme.

Busy Channel Lockout ("Smart PTT - On Correct NAC") that works well to greatly reduce the chances of users "doubling" with eachother, even on repeaters with a long hang time. On the newer P25 radios, the P25 status symbols can be used to prevent transmission on a busy channel, but still allow transmission to a full-duplex console or phone patch.

Conventional Network ID's (NAC's) and talkgroups allow great flexibility in separating groups of users on the same channel, simplex or repeater. Talkgroup 65535 can be used as an "ALL CALL" talkgroup.

More efficient phone patch dialing (Quantar/DIU setup) than DTMF. There's less chance for dialing errors, and you can send over 30 digits in a 90 msec burst of data.

Voice and data/AVL comms can share a channel more seamlessly than analog.

More consistent audio levels than analog if "Digital AGC" is used on all system radios. Although the 4kbps IMBE vocoder is far from perfect, I usually prefer it over analog narrowband.

Any P25 encryption sounds much better than any 12 kbps DES, DES-XL, or DVP etc... And the key ID is transmitted with each frame, so a radio that stops scanning in the middle of on an encrypted transmission can decrypt it with the proper key.

And there's probably a few more that I can't think of right now...

Post by Pj » Fri Jan 27, 2006 2:48 pm

Think of the swtich from analog to digital cell phones... More options and uses/feature can be accomplished due to the "digital" nature.

poser · Post by **poser** » Fri Jan 27, 2006 5:39 pm

Thanks! BTW: what do users hear when they scan into digital unencrypted transmissions?

RESCUE161 · Post by **RESCUE161** » Fri Jan 27, 2006 10:25 pm

It depends on what they're using to scan with. If they have a digital scanner, then they'll hear the transmission in the clear. If it's an analog scanner, then they'll hear a digital sound, kind of like an EDACS control channel on crack.

poser · Post by **poser** » Sat Jan 28, 2006 5:54 am

Thanks!

poser · Post by **poser** » Sat Jan 28, 2006 5:58 am

So the D Star Icom U82 isn't truely digital then, since the signal is still analog?

RESCUE161 · Post by **RESCUE161** » Sat Jan 28, 2006 8:00 am

I think it is AMBE, not IMBE.

poser · Post by **poser** » Sat Jan 28, 2006 10:45 am

I'm sorry, what is the difference between these protocols?

kd5wyu · Post by **kd5wyu** » Sat Jan 28, 2006 10:49 am

The Icom D-Star Radios are digital, they just use a different codec than the ASTRO radios do, so they won't decode on P25 radios or P25 capable scanners.

It is an open format, so the scanner manufacturers could build that into their receivers (unlike M*/*** P********)

(Advanced Multi Band Excitation on Icom vs Improved Multi Band Excitation on the Moto ASTRO gear)

If you are listening to IMBE on an analog radio, it will sound like this
(D-star sounds rather similar)

http://www.kb9ukd.com/digital/astro-imbe.wav

This page also has a whole bunch of other digital mode samples on it that are useful for audibly identifying "what the &#&# is that awful noise I just heard on my scanner / HF receiver?"

-b-