[aprssig] Handheld APRS antennas in the woods (and donations)

Robert Bruninga bruninga at usna.edu
Mon Jul 24 19:44:29 CDT 2017


As we are considering building a 2000 mile permanent Appalachian Network
for APRS Hikers in the woods, the idea of frequency comes up.  Here are the
driving thoughts, but are they correct?



1)      VHF works better through trees,

2)      144.39 works to an IGATE sometimes but is way too crowded for
reliability

3)      Some IGates are not two way.  144.39 is just not good performance

4)      But VHF from a rubber duck antenna is poor

5)      But full size 2m antennas on a hikers HT is a disaster in the woods

6)      So is UHF the better trade?  A rubber duck works “better” at UHF
than VHF

7)      UHF is easier to fit into existing APRS digi sites

8)      My measurements show a 7 dB performance hit at 9600, so we will
start at 1200

9)      But the goal will be to operate at 9600 for better long haul
reliability and capacity.



See the plan: http://aprs.org/ec9600net.html



SO today, I did a quick test to compare an HT rubber duck to a calibrated
spectrum analyzer to see if the 9 dB greater path loss at UHF was in fact
improved by the poorer effectiveness of the rubber duck at VHF.  My test
was inconclusive and limited by reflections.



At first the UHF signal was in fact 9 dB worse than the VHF implying the
path loss was correct, but also implying the rubber duck was as good at VHF
as it was at UHF (that cannot  be!).  So we repeated the test and found we
could get UHF performance anywhere form -9, -7, -2 and even +3 dB compared
to the VHF.  I ran out of time.  Need to do more testing.  Also a human
hand was not holding the HT.  I was using 3 element beams on the SpecA to
reduce reflections…



So before I waste any more time, does anyone have a reference to the actual
on-air quantifiable performance of the rubber duck on the two bands  and
not just a “it works” comparison?



DONATIONS:  Also, when we come up with the design, we will also be asking
for DONATIONS to support the network and in particular, we would love to
find someone that has a stack of 16 UHF commercial grade radios we could
get for the purpose cheaply. We will be doing 9600 baud eventually and want
to have a consistent interface…



Bob, WB4APR
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