[aprssig] Digi Hops to Gate

Stephen H. Smith wa8lmf2 at aol.com
Mon Dec 23 16:56:45 EST 2019

On 12/23/2019 3:22 PM, Matthew Chambers via aprssig wrote:
> In theory how many hops should a packet with *ideal* coverage and digi/igate 
> setups need to find an igate?

1)  There IS NO way to say!  It depends totally on how many igates and 
digipeaters are in the area, and the nature of the terrain.

In California, where digipeaters and igates are on 4-5-6 thousand foot mountain 
tops, the great majority of packets reach the Internet in only one digipeat, or 
even direct.     In the flatlands of the midwest, where it's a REALLY BIG DEAL 
to get a fixed station antenna up 100 feet, the coverage of individual igates 
and digis will be far far less. Even three digi-hops may not reach an 
igate.     Since the incidence of hams (who volunteer to put up digipeaters and 
igates) tends to follow the density of population in general, APRS coverage 
tends to be far better in major population centers.   In most of the mid-west, 
APRS coverage tends to be islands of coverage around large and medium-sized 
cities with large gaps in between.

2)   What you see on APRS.fi, findu.com or any other Internet-based APRS 
display doesn't tell you anything except that you reached the Internet.   You 
may have reached other igates over fewer hops, but if they REACH THE INTERNET 
later (slow Internet connection, ???) you won't see any evidence of them.  [The 
APRS Internet System rejects duplicates of the same packet -- "first man in 
wins!"]     You CAN NOT study APRS RF propagation via Internet results.

> I have my tracker set with proportional pathing thinking I'd be helping with 
> traffic congestion if that were ever a problem here. But only the packets 
> with Wide1-1,Wide2-2 paths ever find an igate and I only know 1 or 2 of the 
> hops since it appears that most of the digis here are not inserting their 
> callsign into the path along the way.

3)   Digis inserting or not inserting their callsign has no effect on the 
number of hops used.  You have to look at the final path used.    Hops of the 
path used up are denoted in the string with an asterisk.

If the final path looks like
    WIDE1-1*,WIDE2-2       then only one digi hop was used to reach the igate
    WIDE1-1*,WIDE2-1       then two hops were used to reach the igate
    WIDE1-1*,WIDE2-0*     then all three potential hops were used to reach the 
    (This last one may show as WIDE1-1*,WIDE2* instead, depending on the 
software used.

regardless of how many calls were added to the path.

> I'm in Central Missouri and packets have to go to Louisburg KS or 
> Edwardsville IL before they get to an igate which means it looks on APRS.fi 
> like I'm driving as the crow flys to the post office and walmart even though 
> i'm certain I made some hundred or so turns along the way.

4)   The straight line you see on APRS.fi DOES NOT denote your track line. It 
only serves to call attention to the Internet entry point for  your 
transmission.  The string of red dots connected by cyan lines is your track line

> I'm contemplating turning off proportional pathing to see if that makes a 
> difference,

5)   "Proportional Pathing" is the alternating of long paths occasionally, and 
short (or direct paths) frequently.    The primary purpose of APRS is NOT to be 
seen on the Internet.  The primary purpose is   (or at least is supposed to be) 
   to be seen by stations on RF.  Normally these would be relatively close to 
you; i.e. in your city or county rather than in a city hundreds of miles away.  
The assumption is that you need fewer (or no digi hops; i.e. heard direct) to 
be seen by these users.  These short or direct paths can be repeated more 
frequently, without congesting the channel for users at the other end of the 

Turning off these short- or no-path beacons is NOT going to make you reach 
distant cities on long paths any more reliably.

> and would more igates make a difference?

6)   YES!!     Having one or more igates in your own local area will ensure 
that even the single-hop short paths  get heard and passed to the Internet.


   Stephen H. Smith    wa8lmf (at) aol.com
Skype:        WA8LMF
EchoLink:  Node #  14400  [Think bottom of the 2-meter band]
Home Page:          http://wa8lmf.net

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