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
spots at telnet.reversebeacon.net, port 7000 and
arcluster.reversebeacon.net, port 7000
UR RST IS ... ... ..9 QSB QSB - hw? BK