[aprssig] PHG in APRS and Xastir?

[VE7GDH]

Bob WB4APR wrote...

> I was surprised to see an Xastir station without any
> PHG data.  I thought UIview was the only software
> that omitted this fundamental dimension to APRS?

Given that we are "told" to fudge the PHG figures to try and make it look 
like the real-world coverage, just how useful is the PHG data that a station 
beacons? I find it more "interesting" than useful, but I'm not using it for 
DFing. I would take the PHG data from ANY station with a large grain of 
salt. I just can't see how you can consider it really meaningful when real 
"per the book" PHG figures aren't usually used and just don't come anywhere 
close to accurately showing the coverage area of a station. Besides, the 
spec doesn't specify if the gain of the antenna is compared to isotropic 
(not too many people have one of those), to a quarter wave, to a half wave 
or what. To top it off, most people seem to have a difficult time deciding 
(or understanding) what their height above average terrain is... unless they 
live on a prairie.

Re fudging... any chance the PHG algorithm is fundamentally flawed? PHG 
sounds good in theory, but just doesn't seem to come anywhere close to 
reflecting real world coverage. Maybe PHG should be just that... power / 
height / gain and not be fudged to reflect real world coverage. Would your 
recommendation be to use "per the book" PHG figures or fudge them when the 
"by the book" PHG shows a ridiculously small PHG circle compared to real 
world coverage? If you or someone else were re-writing the APRS spec from 
the ground up, would you do anything different with PHG second time 
around... or should PHG figures just not be fudged?

> We are trying to track down a CPU Voice signal on
> 144.39 using the APRS Omni-Signal Strength technique
> and I find that almost all home stations in the area are
> not showing any PHG data and so without this fundamental
> APRS data that should be in every position beacon,
> we are having to do a painfuly slow collection of manual
> PHG data.

Good luck tracking it down. I hope PHG data isn't the only tool in your 
arsenal.

> This is a royal pain for something that was supposed to
> be fundamentally included in APRS all the time. Can
> the Xastir authors consider making users enter their PHG
> data at the same time they do their initial set up of callsign,
> lat and long?

My opinion would that it would be far more useful to just use a topo map or 
have a topo map underlay and use my own judgement for the probable coverage 
of a station. Real world example... there is a high elevation digi about 155 
kM east of me. I accidentally bumped the power button and turned my TNC off 
he other day. That digi disappeared from the APRS-IS for a couple of hours 
or so until I turned it back on. The digi is at the east end of an east-west 
valley with a fair number of other digis between it and a bunch of IGates 
off to its west. I'm SW of the digi and even further away with just as 
"clear" a shot at it as everyone else in between. The "missing" digi showed 
up to the rest of the world via my IGate after my TNC was powered back up... 
with just a quarter wave antenna on my end. My PHG data is fudged to reflect 
realistic coverage. However, whether I entered "per the book" PHG (very 
small PHG circle) or fudged PHG data (real world coverage), there should 
still be another 100 kM or so from the edge of my PHG circle to the 
gone-missing digi. I'm not trying to say that my real coverage would include 
mobiles down in the valley below that digi, but if the location of that digi 
was the source of a signal you were trying to track down, my PHG data would 
be pretty much useless in your search. My opinion is that PHG is more 
interesting than useful unless all the PHG figures are entered per the book, 
and even then should only be taken as a guide to coverage.

73 es cul - Keith VE7GDH
--
"I may be lost, but I know exactly where I am!"