[aprssig] PHG and HAAT

Brian Webster bwebster at wirelessmapping.com
Thu Oct 13 21:21:07 CDT 2005

>>comments in line

> While it won't be completely
> accurate it would be much more like reality than a PHG
> circle.

Huh? Then why would we go to the trouble to change the existing PHG
protocol? I guess what I'm saying is if PHG isn't accurate and your
approach isn't accurate then it sounds like we're wasting time. I can't
ever envision any protocol that would be 100% accurate anyway so why are
we even really talking about this anyway? Seams to me like we're trying
to split hairs. No protocol that depends on input from humans can ever
be 100% accurate.

>> This polygon method would at least show where the station had a packet
sent/received at another location/station real world actual data. My comment
about it not being 100% accurate was based on the fact that there would be
places the digi/station might be working but without an APRS station there
to receive the packets one will never know it. This method would not require
input from humans as it would be culled from off the air packets and the
paths they took. All automated and nothing fiddled with.

Don't forget any change in protocol that would display RF data would
leave all current clients without anyway to display the new protocol. So
you would go from just one client that doesn't natively support PHG to
all clients not natively supporting the new protocol. Then you'd have to
work at getting all client software updated. After that point in time
you'd have to go back and reeducate people to download the new software
and explain to them how to correctly enter new data into a new client.
Wow I'm tired just typing about it. ;-)

>> I'm pretty sure this could be made to work within the confines of the
object area format that exists. This would display a polygon in the same way
you can display a weather watch area on a map now. This would not require
any changes in existing client software nor force upgrades. My thought would
be to have some server that could calculate these points, create the polygon
format it in proper APRS packets then be able to display it on a map and or
broadcast the same data when a query was sent. I'm not a programmer so I
don't know exactly how this would be implemented.

Would seam to me it would be easier to just educate people and tell them
that PHG circles are only an educated guess (if entered properly) at the
possible coverage of the transmitter on a good day when the wind is
blowing from the correct direction with a full moon rising.

>> We can't even get folks educated on paths and/or digi upgrades, what
makes you think we could get them to properly use the PHG system, it
obviously hasn't worked to date ;-)

>> In areas where you don't have an omni directional pattern due to terrain
limitations the circles do not reflect the true coverage area of a

I still somewhat of a newbie so help me out here. How can you get a
negative number for HAAT? Did you dig a hole and put an antenna in it?
It would seam to me the lowest HAAT number you could come up with is
zero. Zero meaning your not gaining anything over the average height of
the surrounding terrain.

>> HAAT by the FCC definition (and I am quoting from memory and might have
parts of this wrong) are that you draw 36 radials out at 10 degree intervals
from your location. You then take 50 evenly spaced elevation data readings
between 3 and 16 km along each of the lines. These get averaged and a number
is derived. I have many locations along these radials from my house that are
four to five hundred feet above my elevation when I trace out the lines to
16 km away. This is how you get a negative number. The Height is above the
average terrain around you in a 16 km radius. This is why it  gets difficult
to just guess at the number by looking around you in a hilly area. In your
transmitter is located in a deep valley you will most likely have a negative
number for your HAAT. There used to be a web site that allowed you to look
this information up, it disappeared a year or so ago. Too bad as it was a
great tool and there does not seem to be another on line source to calculate
this critical piece of information.

My opinion; UI-View's problem is not that it doesn't display PHG circles
but that it doesn't naturally transmit PHG circles.

>> Brian N2KGC

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