Pete asked for a note describing my RBN receiving system but
a precautionary note is in order -- I am not an engineer and my views are not
authoritative. My location is an
advantage. I am in a semi-rural
environment 100km west of the New Jersey coast.
The vertical antenna is in the woods where the radials are in wet soil part
of the year.
The Antenna
I was introduced to SDR units by playing with a KB9YIG SoftRock
kit and I became persuaded of the importance of controlling the impedance of the receive antenna. When Alex introduced
Skimmer Server I decided to purchase the QS1R but was perplexed by what kind of
omni-directional antenna system to install that would have reasonable impedance
on all of the bands, including 160m and the WARC bands, if possible.
he active vertical antenna similar to the
Clifton Laboratories Z1501D was an obvious possibility but Jack's antenna
wasn't quite ready at the time and I had a bias toward putting up a vertical
that could serve as a transmitting antenna if my interests changed.
The excellent study of HF vertical
performance in 2000 by N0AX and K7LXC excluded several multi-band verticals
from my consideration. I liked the HyTower
verticals installed in my 80m array and decided to install that antenna's
"little brother", the HyGain HyTower Jr, a 39 foot (12m) vertical
with wire "cage loading" on 80 and full size wire elements on 40, 20,
15 and 10 meters. It is a design that has
been around for decades and it is simple enough that I understand how it works
so I can repair it when it breaks. Mine
is not guyed.
Of course the key to
making this work is the radial field so I purchased four 500' rolls of #14
insulated solid house wiring and cut each roll into 8 equal pieces resulting in
32 radials, each 19 meters long. I use
the DX Engineering radial plate and feed the vertical with about 90 meters of Davis
RF Bury-Flex through a Polyphaser
lightning protector. After the coax
losses this system has an impedance between 23 and 78 ohms on all ten bands
from 1.8mHz to 28.3mHz with the exception of 18.1mHz where the impedance is
about 148 ohms.
The Pre-Amp and Receiver
I tried using the QS1R with no preamp but it was obvious
that other RBN receivers were hearing stations above 14mHz that I could not hear so I added the
Clifton Laboratories Z10040A 11db amplifier for a big improvement in the number
of spots I detected.
The Computer
The initial computer was a Intel Q8300 Core 2 Quad running
Windows XP which worked fine except for the CQ WW DX contest when it failed at
about 2800 decoders. This has been
replaced with a Windows 7 64 bit Intel I7-3770 which has yet to be truly tested
in the CQ contest, but seems to work fine.
I use the W3OA Aggregator to change bands during the day.
