I hooked up the hub today, and initial results are excellent.
For those who missed earlier messages - here's the story. I ran across
an inexpensive 8-way relay board on E-bay for less than $20. It is
controlled by a 300-MHz radio remote, and I figured I might be able to
use it for remote switching of receiving antennas. Rather than try to
boost the radio control signal with a directive antenna, Ian, GM3SEK
encouraged me to experiment with coupling the RF from the remote to the
350 feet of coax out to the planned hub location, using a 1-inch loop at
each end. It worked!
As with many such projects of mine, this one mushroomed a little bit. I
added a 20dB ARR preamp at the hub, using DC sent to the hub from the
shack with a DC bias tee, which was needed for the relay board anyway.
Rationale for putting it out there, rather than in the shack, was that I
plan to use low-output antennas (BOG, K9AY, etc.) and wanted the desired
signal to be as loud as possible relative to any common-mode pickup on
the feedline. I also used a super common mode choke near the hub, per
ON4UN and K9YC.
Since I only had one good 9:1 binocular transformer, I decided to share
it among the antennas that will be connected to the hub. A little
fiddling with TLW and various impedances and reactances convinced me
that the extra cable loss caused by mismatches will be quite manageable
for 160 and maybe 80 meters.
I was worried about isolation between antennas, because the relay board
was not designed for RF, but early indications are positive. A local
broadcast station, on 1550 KHZ, is S9+60 on the BOG, and just S9 when I
switch to an unused terminal, even the one physically adjacent. Signal
level is only slightly below that received on my shunt-fed tower
Now to build a proper control unit - For $18.50 I'll buy another relay
board and use it with push-button switches and LEDs to display which
antenna is selected. Thanks to Grant, KZ1W for this suggestion!
I'm curious - does anyone think there would be enough interest to
warrant writing this up for one of the mags?
--
73, Pete N4ZR
The World Contest Station Database, updated daily at www.conteststations.com
The Reverse Beacon Network at http://reversebeacon.net, blog at
reversebeacon.blogspot.com,
spots at telnet.reversebeacon.net, port 7000 and
arcluster.reversebeacon.net, port 7000
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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