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[aprssig] PHG part II

Heikki Hannikainen hessu at hes.iki.fi
Tue Jan 13 13:47:27 UTC 2009


   Hi,

On Tue, 13 Jan 2009, Dave Baxter wrote:

> Having tried to add PHG to my beacon text, both Findu and APRS.fi are 
> not showing any range circles. (Digi Call = G8KBV)

   At least aprs.fi is showing it nicely, you just need to enable the 
circles, they're disabled by default. Click on the "circles" icon in the 
top right corner, third one from the top.

> What I have as the Beacon Comment text in UiView is "PHG2134/ 5W WIDE1-1 
> Digi." no quotes.  On both Findu and ARPS.fi, the / is showing as part 
> of the comment.

   That seems right. Maybe I should strip the "/ " from the beginning of 
the comment to clean it up.

> Err..  4W?   Feeder loss?

   The values are encoded in the PHG extension in a fairly low resolution. 
Power steps are 0, 1, 4, 9W, 16W... see the specification at:

ftp://ftp.tapr.org/aprssig/aprsspec/spec/aprs101/APRS101.pdf page 28 (PDF 
page 38), Chapter 7: APRS Data Extensions.

   There's also Bob's "mobile range" document at:

   http://aprs.org/symbols/PHGmobile.txt

> And the actual range is a darn site more than 5 miles, that I know for sure.

The range calculation formula is in the specification. It's nowhere near 
reality, and it's not trying to be, it's simply impossible to get it 
truely right with such a little bit of inaccurate information. You'd need 
information about the other station's antennas and power, and take into 
account the terrain and buildings around your station. It just gives a 
very rough idea which digi is supposed to have somewhat larger coverage.

If you know (from looking at the list of heard mobile stations) the true 
range is different than what was calculated from PHG, it's a good idea to 
increase or decrease the antenna gain in your PHG transmission to 
compensate for this.

   - Hessu, OH7LZB




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