[aprssig] PHG in APRS and Xastir?

[Robert Bruninga]

> just how useful is the PHG data that a station 
>beacons? I find it more "interesting" than useful...

PHG is intended to show RELATIVE performance in
the RF domain which is what ham radio is all about.

There is a 1000-to-1 difference between the 
coverage area of a 5W station with a 10' antenna
and a 50W station on a hill with 300' height above
surrounding terrain.  PHG plots are intended to show
this big difference.

RF is a very varried thing.  PHG should not be
interpreted as RF lines on a map.   We need to get 
people to view them as intended and that is to show 
RELATIVE performance.

>I would take the PHG data from ANY station with 
>a large grain of  salt.

Yes, I agree.

>...the spec doesn't specify if the gain of the antenna 
>is compared to isotropic  or what. 

The 2 dB difference is not all that significant (in what
PHG is trying to do), but it was supposed to be isotropic.
There are many greater errors and  greater discriminants
 in quantifying radio range that are more important.

>To top it off, most people seem to have a difficult 
>time deciding  (or understanding) what their height 
>above average terrain is...

The hams that are unfamiliar with the difference in radio
range  between being on a hill or in a valley, need to learn
more about their hobby.  We need to help educate them.  
And letting them see the effect of height in their PHG 
circle is a great way of helping them visualize it.

>PHG sounds good in theory, but just doesn't seem 
>to come anywhere close to reflecting real world 
>coverage.

We need to change those expectations and guide them
toward what PHG is supposed to do.  It does do an 
*excellent* job at showing the relative difference in 
performance of the variety of stations we have on APRS.
There are big differences of 10, 100, 1000, & 10,000-to-1 
differences in performance of stations on APRS.   Omitting 
the PHG information does a disservice to the RF dimension 
of APRS.

> Maybe PHG should be just that... power / 
>height / gain and not be fudged to reflect real world 
>coverage.

I think you are on to something here.   And this
recommendation is probably a good idea.   Because
the inference to "tweak them to performance" does
imply a greater degree of "precision" that we both
agree does not exist.

> Would your recommendation be to use "per the 
>book" PHG figures or fudge them...

If you can point me to where I had preciously suggested
"tweaking" them, I will be  happy to go back and
change them, because I agree, it is getting people on
the wrong track here...

Thanks
Bob, WB4APR