[OZAPRS] FW: [Fwd: 70 cm APRS frequencies]

Bob Bruninga bruninga at usna.edu
Fri Nov 21 10:29:50 EST 2003


On Wed, 19 Nov 2003, Richard Hoskin wrote:

> When this subject came up a year or two ago John Martin/Peter Hallgarten
> suggested we use 439.100Mhz for a National UHF APRS frequency but due to
> the other issues the WIA never ratified this in the band plan.

WB4APR's 2 cents for what its worth...

1) APRS is a SINGLE frequency tactical system for end users.  There is no
need or desire (in general) for other than one freq.  Everyone wants and
needs to be "where the local action is"...  (If everyone is not on the
same channel, then everyone is not seeing the same tactical information)
and you dont have a real-time tactical system...

2) UHF for single UI mobile packets is MUCH WORSE than VHF due to
triple the mobile flutter rate and 9 dB worse path loss dipole to dipole
and 7 dB worse modem detection...

3) APRS needs  UHF backbones to tie the long haul packets between end
users on local LANS operating on the single national frequency.  These
cross links and backbones CANNOT all operate on a common UHF frequency
(hence, there is no need for a "common APRS UHF frequency))...

4) Mobiles (think Kenwooods and HAM-HUDS) have NO NEED for LOTS of
incoming megabytes of positions from anywhere but their local area.  They
cannnot display it and the driver cannot ABSORB IT.  THus there is NO NEED
for UHF or 9600 baud to imporve the SPAM rate to mobiles...

5) CONVERSLY, those with full displays and PC's are usually fixed.  THey
DO WANT TO SEE lots of stuff.  But they are FIXED and LOCAL and so they
have no problem "remembering" their local UHF backbone or LINK.  Again,
there is no need for a common (mutually interferring) high speed UHF
backbone frequency.  For best integration, it is desired that all high
speed UHF feeds use DIFFERENT channels to completely avoid the mutual
interfere3ce and to give dedicated full time access.

So my conclusion after looking at this for YEARS, is that there is just no
need for a single coordinated UHF APRS channel.  But there is a need for
EVERY local APRS lan to coordinate a LOCAL UHF channel (different from
their 4 neighboring LANS) to feed high speed data to the LAN...

Just my two cents...
de WB4APR, Bob


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