I had played around a bit with a corner-fed, corner-terminated "Superloop" (
http://www.bamlog.com/superloop.htm) last fall, but foolishly tried to make
it too big and unwieldy to put up and take down every time, and was still
lacking in knowledge about how to really do this stuff. Broadband was the
key; my tuned loops have worked very well, and even more so when phased
with a tuned vertical, but don't fully take advantage of an SDR.
This time I was more practical and decided to limit the height of the
antenna to 7 feet, so I can reach the top. Length-to-height ratios of
about 3-to-1 or 4-to-1 give the best modeled front-to-back signal ratios
for the cardioid pattern, so I've settled on a 24-foot length for now.
That's about as long as I can go and still set it up in a wide range of
orientations.
I've always been more of a software person than a hardware person, but I'm
using my renewed DXing interest to work on that. So, I put together a
proper connection box for a potentiometer for the terminating resistance,
and wired up a 16:1 impedance matching transformer on the recommended
Fair-Rite 2873000202 binocular core for the feed line connection box. Due
to the low dynamic range of my inexpensive SDR setup, I used a pair of
Mini-Circuits filters to make a steep low-pass filter for my local
1450/1490 pair (and higher frequencies, of course) and thus can make use of
higher amplification. For the latter, I hot-rodded a commercial
upconverter with a semi-commercial low-noise amplifier on a bare PCB and my
own ham-fisted soldering. The cheap RTL-SDR dongles have built-in
amplifiers, but you get what you pay for.
I still want to do some rigorous daytime testing to measure front-to-back
ratios and such, but I had my first chance for some nighttime testing on
the 25th. I decided that the most obvious test would be to point the
cardioid pattern at 130 degrees into Mexico and do an SDR recording over
the 10pm MST TOH (5UT). Indeed the dial was dominated by Mexican stations
(including a new log of XEPRC), along with Texas and New Mexico, plus a few
strong stations off the back end.
Work and life (and work) got in the way. But, Saturday morning, I set up
at about 280-290 degrees for the 2am TOH (9UT) and had pretty much the
opposite with lots of California and Utah, a long-awaited confirmation of
920-KBAD out of Las Vegas, and several Canadians. After working through
that SDR file, I swapped the antenna boxes to point to about 105 degrees,
hoping to catch some stations to the east on day power at the 5am MST
(12UT) TOH.
That worked out insanely well with 7 new stations! Admittedly, if I'm
DXing at that hour, it is almost always for trans-Pacific stations, one of
the planned uses for this antenna. Thus, there's a lot of untapped
potential in the eastern sunrise option. But, I was not expecting such a
bounty. Using an SDR really seemed like cheating!
Other pointings Sunday morning were not so fruitful, but I did pick up
another new station and as often the case with TOH recordings, I added some
new call recordings to my collection.
So, the 10 new stations from these tests put me up to 486 stations since
August 15th, 410 of which have been logged with their call letters (not
always on the first log, though), and most of the rest on slogan/webcast
combinations. I have recordings of about 90% of the call letters. About a
dozen of the logged stations without call letters are Canadian or Cuban
where it will be very difficult to ever get call letters, but the rest
should eventually be amenable. Also, some of the unrecorded calls are
common stations for which I'm only bothering if they are coming in
particularly well.
I hope to put together a blog post with pictures and other details
eventually, and especially some daytime signal strength testing. May not
be useful for all of the highly experienced people here, but I like putting
this stuff together anyway.
Brian Rachford - Prescott, AZ
azswdxing@xxxxxxxxx
http://azswdxing.wordpress.com/
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