National messaging system

[dubose at texas.net]

Curt Wrote:
> On Tue, 18 Jan 2005 dubose at texas.net wrote:
> If you look at page 17 of KN6KB's SCAMP presnetation to the DCC, you see that
> he shows Pactor III and SCAMP at less than 200 WPM at a -5dB SNR on a poor
> CCIR channel.  And if you look at G4HPE's DCC paper on MT63, you see that it
> has 200 WPM at a -5dB SNR on a poor CCIR channel.  Part of what I hear from
> the League is that Pactor III and some other users is Ok under good signal
> conditions but isn't very good under poor conditions.

    I know I'm rehashing some stuff that's been discussed before, but I
    don't have the old messages in front of me at the moment:  Isn't
    Pactor-III the really wideband mode where you might get one
    connection at a time going on one frequency, but we don't have much
    more room available on 30M or other bands for much else?

   Pactor III is 2.4 KHz wide and has a thoughtput of close to 200 WPM at a 
   -5dB SNR on a poor CCIR channel.

   MT63 has a 2 KHz mode that provides 200 WPM throughput and will provide 
   this throughput down at -5dB SNR on a poor CCIR channel.

   Rick's, KN6KB, SCAMP is about 2.4 KHz wide (maybe 2.7) and has a 
   throughput averaged multi-path poor CCIR channel and -5dB SNR about the   
   same as PIII

   The advantage of MT63 is it runs on a soundcard not proprietary hardware.

   Sure a lot of Pactor III and MT63 2 KHz signals on 30M is going to crowd 
   the band...but I've never heard 30M crowded.  I may just have missed the 
   pileups. Hi Hi.


Isn't it comparing apples and oranges between the narrow and the
wideband signals?

      Sure, but Pactor III, SCAMP and MT63 are  all wideband 
      signals...between 2 and 3 KHz.

It seemed from earlier discussions that Pactor-III was going to have
limited uses except perhaps in emergency situations where of course
they could take priority on the bands (where the emissions are
authorized) to get traffic through.

   I think that the WinLink folks and the ARRL expect it to be running all
   the time.  The limiting factor is that Pactor II and III require an 
   expensive controller and Pactor I doesn't...that is if the KAM controller
   isn't considered expensive.  Pactor I can also be run using a PK-323 that
   has been upgraded.

If we can use narrow signals or perhaps multiple narrow signals we
might be able to use the system much more, on more bands (frequency
agile depending on MUF and distance of QSO), and get more practice
during non-emergency times with the system.

   Maybe but right now the the wider the bandwidth the more data you can
   push though.  If you have several narrow signals, you will have overhead
   with each one so put the overhead on just one signal.

Let me know if I'm all wet here.  I'm near Seattle so I'm used to
it.

   Its been raining in CAlifornia and Texas...and cold in Texas.


> probably considers robustness to be around -5dB SNR on a poor CCIR channel and
> that something at or above 200 WPM is the minimum throughput.
>
> Right now all is relative and I admit a guess (SWAG perhaps) and will remain
> so until the League comes out with some specs for a highspeed, robust HF mode.

A reasonable WAG (is that an oxymoron?).

    SWAG...we want to be scientific here.

73,

Walt/K5YFW

--
Curt, WE7U.   APRS Client Comparisons: http://www.eskimo.com/~archer
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