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[aprssig] Igates Are A Fair Weather Solution (was: "Finito")

Jim Lux jimlux at earthlink.net
Mon Aug 29 18:03:24 UTC 2005


>
>Message: 8
>Date: Sun, 28 Aug 2005 17:52:50 -0700
>From: "Ray McKnight" <shortsheep at worldnet.att.net>
>Subject: Re: [aprssig] Igates Are A Fair Weather Solution (was:
>         "Finito")
>To: "TAPR APRS Mailing List" <aprssig at lists.tapr.org>
>Message-ID: <005a01c5ac33$fbf64ee0$0fa8a8a8 at bigserver>
>Content-Type: text/plain;       charset="iso-8859-1"
>
>I don't disagree with these arguements.
>But you make a few assumptions that I feel should be addressed.
>
>How many people have said "gee, I never even considered using HF"!
>Yes,  the perfect tool for reaching beyond your local area, especially
>out to 400-500 miles!  Plus, you have virtually UNLIMITED frequencies
>at your disposal to set up small, specialized nets for specific traffic or 
>between
>two users needing to pass high volumes of traffic.  PACTOR is PERFECT for 
>this as it can *reliably* maintain a connected link with error correction 
>down to -18db BELOW the noise floor!

Which version of PACTOR?  I doubt that PACTOR I (which is what low end 
modems support) would fit the bill.
And, I've seen that -18dB claim (in the context of Pactor III) a number of 
places, but find it hard to believe. (Shannon and all that) How is "noise 
floor" defined here?  The total power in a 3kHz SSB channel?  Pushing a few 
hundred bits/second through a 3kHz wide channel with negative overall SNR 
is certainly possible.

Pactor III is expensive enough that it's beyond the "casual experimenter" 
(figure about $800-$1000 or so, by the time you get a SCS modem, cables, etc.)


>Even VOICE would be a better solution in most cases for the long haul vs APRS.

Indeed... no special hardware required, makes optimum use of context 
sensitive error correction, minimal training of operators required.

One might find the experience of the HFPACK folks useful. They're into 
minimalist portable systems (Pedestrian Mobile, etc.)


>Message: 9
>Date: Sun, 28 Aug 2005 22:30:43 -0500
>From: Patrick Green <pagreen at gmail.com>
>Subject: Re: [aprssig] Igates Are A Fair Weather Solution (was:
>         "Finito")
>To: TAPR APRS Mailing List <aprssig at lists.tapr.org>
>Message-ID: <54e5072305082820307706cd74 at mail.gmail.com>
>Content-Type: text/plain; charset=ISO-8859-1
>
>APRS relies heavily on infrastructure.  In an emergency,
>infrastructure will probably not be available.  HF is good because you
>rely on your HF radio and an antenna system, both of which you can
>have on the ready.  Having an APRS network on the ready is harder but
>not impossible but don't rely on your local digi to get you out.  I
>have a digi setup here in town but it isn't on power backup.  For my
>shoe string budget, it would be costly to get UPS backup for the digi.
>  So when that disaster strikes, you can count the intown digi probably
>won't be there.


And remember that antenna tuner.. When you throw that wire up over the 
wreckage to use as an antenna, you're going to want a tuner.



Jim Lux, W6RMK 






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