When we initially installed the K1XC Repeater
Stack, 2M, 70CM and 23CM modules I tried a Comet
Triband antenna and triplexer. It was a disaster
with all kinds of interactions and de
sense. When we changed out the system to 4
separate antennas (2 antennas for 1.2 Voice and
data) most of the problems went away except for
the 70CM module. The problem was we reused a
dual band (2M/70CM) comet antenna for the 440
module and it wasn't resolved until we replaced
the 440 antenna with a 16 bay folded dipole array
tuned for 70CM only. As others have stated, our
bands are harmonically related - 2M X 3 + 70CM
and 70CM X3 = 23 CM (not exactly but close enough to cause interactions).
When we installed the W4PLB D-STAR repeater (our
second site) we used separate 2M and 70 CM folded dipole arrays.
Also as Evans, stated, If a Comet or Diamond
fiberglass antenna is hit by lightning, you get
toothpicks (more accurately, fiberglass
fragments) they literally explode (heating
causes the air inside the fiberglass radome to
rapidly expand and the result is a shower of
fiberglass fragments). I've had it happen 2
times here in central Florida. Go with the DC Grounded commercial units.
Also use Double shielded Coax (Like RG-214 or
RG142B/U) or hardline for all connections between
the antenna and the Repeaters (especially between
the Duplexers, any preamps and the
Repeaters). Remember 98% shield still has 2%
"Holes" where RF can get in. Cheaper cables are
even worse! Also keep in mind that the
Duplexers only notch out the Transmit frequency -
they allow many "out of band" signals in. We use
DCI bandpass filters in front of the preamps to
keep out signals that get through the Duplexers.
VRY 73
Bob Cumming
W2BZY
President and Repeater Chairman Orlando ARC
K1XC and W4PLB D-STAR repeaters
KB4UT and N4UMB analog repeaters
QRV 160M - 9CM + 3CM (5760 next)
from EL98hr
At 09:57 AM 4/20/2010, you wrote:
If you are installing a D*Star repeater stack (2m 440cm modules) can you
use a single dual band antenna for both modules or do you need separate
antennas for every module in the stack?
