[aprssig] Cross-Band Digi or Gate?
Robert Bruninga
bruninga at usna.edu
Mon Apr 5 21:26:11 EDT 2010
> ... what the proper approach is for gating
> (or is it digipeating?) HF traffic onto local
> VHF frequencies? Is this an ok thing to
> do, or just gate the received packets to APRS-IS and be done
with it?
It was OK back when we first started in the 1990's. Im not sure
about now. With internet connectivity available to everyone,
I'm not sure I see the value in adding QRM to local VHF nets...
> Are there any good (read: current) guidance on paths
> for HF APRS?
The original www.aprs.org/APRS-docs/HF.TXT
But maybe I need to update it to recommend against gating HF
back to VHF? But for SURE, VHF gating to HF is strictly
verboten...
Bob, WB4aPR
>
> HF propagation is constantly changing and erratic. You
> normally will only have a reliable path between any two
> specific locations (like two stations trying to converse with
> each other) for a few hours a day. On the other hand, the
> band is open to SOMEWHERE hundreds or throusands of miles
> away virually 24/7. Digipeating on HF (i.e. between HF
> stations) is severely discouraged since WHERE you would be
> digipeated to is completely unpredictable.
>
> Because of the erratic nature of digipeating on bands where
> propagation is constantly changing, the success rate to reach
> a given station is very low. In an interactive messaging
> scenario, you wind up with endless missed acks and
> re-transmissions that will reduce the already-low 300 baud
> throughput of the shared channel even more. You can easily
> have 8-10 transmissions to get a single message string from
> station A to station B on HF. [Bear in mind that when you
> transmit on HF, you are potentially occupying the channel
> over HALF OF NORTH AMERICA at once!]
>
> The KAM TNCs treat the crossband digipeat as a normal digi
> hop triggered by the name "GATE" in the path. A typical HF
> path would be something like:
>
> WA8LMF > APRS,GATE,WIDE2-1
>
>
> This would use NO digis on HF, cross over to VHF at various
> random and unknown locations over an area of potentially 2000
> miles radius or more (depending on propagation) and then do a
> normal one-hop home station VHF path in each of those
locations.
>
>
> The real question, though, is: Will the locals in these
> various remote VHF areas appreciate having random "DX"
> stations from hundreds (or thousands) of miles away suddenly
> appearing on their local 2-meter channel???
>
> Given that HF is far more suited to one-way beaconing from
> remote locations to random fixed station igates (rather than
> interactive two-way communications between specific users;
> i.e. messaging) , probably just gating HF receive into the
> Internet would be more useful than retransmitting HF posits
> onto VHF. This causes HF fixed stations anywhere to
> become part of an enormous diversity receiving system,
> ensuring that mobile posits from anywhere will always hit the
> APRS-IS regardless of propagation or band conditions. (Since
> you don't care WHAT station injected you into the Internet
> system; only that you got to the Internet.)
>
>
> See my discussion on HF APRS at:
>
> <http://wa8lmf.net/aprs/HF_APRS_Notes.htm>
> <http://wa8lmf.net/aprs/HF_APRS_Notes.htm>
>
>
> for more details on HF operations.
>
>
> ________________________________
>
>
> --
>
> Stephen H. Smith wa8lmf (at) aol.com
> EchoLink Node: WA8LMF or 14400 [Think bottom of the
2M band]
> Skype: WA8LMF
> Home Page: http://wa8lmf.net
>
> NEW! Universal HF/VHF/UHF Antenna Mounting System
> http://wa8lmf.net/mobile/UniversalAntMountSystem.htm
>
> "APRS 101" Explanation of APRS Path Selection & Digipeating
> http://wa8lmf.net/DigiPaths
>
> Updated "Rev H" APRS http://wa8lmf.net/aprs
> Symbols Set for UI-View,
> UIpoint and APRSplus:
>
>
>
>
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