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[aprssig] Cross-Band Digi or Gate?

Robert Bruninga bruninga at usna.edu
Tue Apr 6 01:26:11 UTC 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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