PHG specifies 
the transmitter
power output,
effective antenna height 
above the average terrain,
antenna gain and antenna directivity. 
APRS uses this info to calculate and plot
radio range circles around stations on maps
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PHG CODE      0       1       2       3       4       5       6       7       8       9     UNITS
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POWER OUT     0       1       4       9       16      25      36      49      64      81    WATTS
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HEIGHT        10      20      40      80      160     320     640     1280    2560    5120  FEET
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ANT GAIN      0       1       2       3       4       5       6       7       8       9     DB
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DIRECTIVITY   OMNI    45      90      135     180     225     270     315     360           DEG
                      NE      E       SE      S       SW      W       NW      N
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EXAMPLE
If you are running 36 watts out
from your radio and your antenna
is mounted on a 80 ft tower
and the antenna gain is 6 db 
and it is a omni directional ant then your
PHG code calculated from the 
above table is 6360
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