SteveRF
Thanks for starting this thread - very
informative. FWIW, here's my experience. I
had done the accessha.com mod, adding the F
connector, coax cable and antenna (from
another site). This did improve the
reception but I still had "dead" areas where
the motion sensors wouldn't work. Well, I
like to experiment so I did the
following...after reading a few manuals on
antenna theory. I first clipped the ground
wire from the F connector (inside the CM15A).
Then added a short (18 inches or so) coax
cable. The cable was stripped at one end so
9.5 inches of the center wire was exposed
(the shield was removed). Then I looped the
coax from the F connector under the CM15A and
up the side so that the base of the bare wire
was about 2 inches above the component side
of the circuit board, and perpendicular to
it. Picture: CM15A horizontal with circuit
board up, soldered side down, coax/connector
coming from side and looping under and up
opposite side of unit with shield ending 2
inches above unit and bare wire extending
vertically 9.5 inches. Really was quite easy
to do since the connector mod had already
been done. Anyway, I found that with the
circuit board acting as the antenna
groundplane the reception was much improved
and the "dead" spots were gone, probably
because this design is more omnidirectional
than the other antenna design (from the other
web site). The distance the base of the
antenna is from the circuit board influences
it's effectiveness, and I found 2 inches to
be best. This resulted in the best reception
for my home variables. I even got the most
distant motion sensor to work - about 75 feet
away through 4 walls. Interestingly, this
is little different from just extending the
wire as discussed in this thread, except that
the wire is shielded. Just thought I'd add
my two cents.