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[aprssig] FRS comms in support of APRS

Robert Bruninga bruninga at usna.edu
Mon Feb 27 22:05:06 UTC 2006


Since we always include FRS voice in our
special event planning, today I compared
every radio I had to a sig gen.  See setup
notes at end:

Kwd TH-D7                0  dB Benchmark
Kwd TH-F6                 0  dB
Alinco DJ-S41            -1 dB
RS 21-1804 #1         -1 dB single ch 1 model
Cobra uTalk290        -4 dB
Cobra LXT305 #1     -5 dB Bought yesterday $12ea
RS 21-1804 #1         -5 dB single ch 1
RINO-110  #1&2      -7 dB but audio very poor
RS 21-1803   #1       -7 dB single ch 1
Motrola T5420          -9 dB
Cobra LXT305 #2     -9 dB
Uniden gmrs540#1 -11 dB
RS 21-1803 #2       -12 dB single ch 1
Uniden gmrs540#2 -11 dB
RS 21-1810             -14 dB  multi ch and tone
Avox GMRS602       -16 dB  two of them

Notes: Ham radios were tuned to 440 MHz
FRS were tuned to channel 1.

I replaced a short antenna with a full size 6"
and the only difference was about 1 to 2 dB,
hardly noticible.

Tests were done with a sig gen and coax to a
fist sized piece of aluminum ground plane mounted
on a board.  The center of the sig gen coax was
connected to a 6" by ½" monopole extending
on the board so that when the HT was layed 
on the ground plane, its antenna was as close
as possible to the monopole.

The best measurement was taken for all radios
by moving my hand, the HT and the antenna
all around to find the strongest signal.  Then
data was recorded.  Some HT's were as close
as possible to the monople.  Others were 3 or
4 inches away to get the best signal.  Others
required my hand, others worked better without
my hand. 

Conclusion from the variable placements is that
the antenna matching is quite varied on 
separate units.  But those vagaries are no
differrent than the normal vagaries of close
proximity holding of an HT...

de Wb4APR, Bob





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