Yes. Since radio propagation doesn't work very well underground :-), the APRS 1.0.1 protocol specification only supports positive altitude values for PHG (chapter 7, page 28). The FCC calculator may be using too large a radius for elevation averaging (i.e., assuming broadcast station towers versus handheld radio transceivers).
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Based on some old discussion threads I found elsewhere, it appears that HAAT/Height for APRS PHG figures and the FCC HAAT are completely different. If a person familiar with general radio theory sees HAAT or someone does a web search for HAAT, they will come up with the FCC version. It seems that I am far from alone in the confusion.
The recommendation I found (I think it was Bob's recommendation) was to put in the nearest values for your station's power, antenna gain, and directivity, then adjust your HAAT number until your PHG circle touches the PHG circle of the farthest station you routinely receive (if it were me I would adjust it until it actually hits the farthest station that routinely hears me, but what makes sense to me may not be how Bob and company envisioned it). Then, alternate tweaking the directionality and height/HAAT to fine tune things to reflect close to reality.
Might be good to include a note about this in the YAAC help file.
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One thing I noticed is that HAAT numbers in YAAC cannot be negative. Is this a PHG circle restriction? My HAAT using the FCC calculator is -83 meters.
Yes. Since radio propagation doesn't work very well underground :-), the APRS 1.0.1 protocol specification only supports positive altitude values for PHG (chapter 7, page 28). The FCC calculator may be using too large a radius for elevation averaging (i.e., assuming broadcast station towers versus handheld radio transceivers).
The FCC uses 50 points per radial evenly spaced between 3 and 16 Km out.
Based on some old discussion threads I found elsewhere, it appears that HAAT/Height for APRS PHG figures and the FCC HAAT are completely different. If a person familiar with general radio theory sees HAAT or someone does a web search for HAAT, they will come up with the FCC version. It seems that I am far from alone in the confusion.
The recommendation I found (I think it was Bob's recommendation) was to put in the nearest values for your station's power, antenna gain, and directivity, then adjust your HAAT number until your PHG circle touches the PHG circle of the farthest station you routinely receive (if it were me I would adjust it until it actually hits the farthest station that routinely hears me, but what makes sense to me may not be how Bob and company envisioned it). Then, alternate tweaking the directionality and height/HAAT to fine tune things to reflect close to reality.
Might be good to include a note about this in the YAAC help file.