[OKDXA] Force 12 Sigma 80 is up!

[Kim Elmore]

I have finished installing my Force 12 Sigma 80 vertical dipole and 
everything went by the book.  Tuning was a cinch and I easily got a perfect 
match.  Resonance is set for about 3520 kHz and the match is acceptable up 
to about 3560 or so.  Since it is a physically short antenna, there is a 
tradeoff in bandwidth.

I have a hal-sloper that I've been using on 80 m. Receive tests indicate 
that very close-in signals are down by about 10 dB, from S9+20 dB down to 
S9+10 dB on the Sigma 80 vs my half-sloper.  Most other receive signals 
sound about the same between the two antennas.

My first QSO was with 5R8FU (I'm sure :) during his dawn.  My experience on 
the low bands is admittedly limited, but this is a nearly E-W path and, 
based on the reading I've done, sounded like a classic gray-line 
opening.  I happened to be on his frequency when his CQ quickly appeared 
out of the noise and rose to an honest 579 RST.  I tried once with 100 W, 
as did someone with an N1 call, but he heard neither of us.  I then 
switched on the amp and got him on the first call, getting a 579 from 
him.  Shortly afterwards, he faded back into the noise, and was 
gone.  Using the Sigma 80 isn't like having a 3 element yagi up a couple of 
hundred feet, and I'm sure that the rx signals will still be 
characteristically crummy on 80 m compared to the higher bands, but this 
will be as good as it gets for me for awhile.

Noise pickup is not significantly different between the two antennas.  I 
live in a very quiet location, so my night-time noise levels right now run 
about S3-S5.  In the day, the noise level is low enough that it doesn't 
move the S meter.

I'd hoped to be able to load the antenna up on 160 m using my tuner, but 
had no luck.  The Sigma 80 uses a hairpin match, and I'll bet that the 
hairpin coil helps generate a very low impedance at 160 m, preventing me 
from getting a match.  All is not lost, however, because I turned up a pair 
of 80 m traps I'd made long ago for a trapped dipole for 40, 80 and 160 
m.  I'll add one to my half-sloper, along with some wire, and see if I can 
get a match on 160 m.  While I can tune the half-sloper for 160 m, I go 
through a remote antenna switch to this antenna, and the antenna switch 
won't tolerate much power with a big mismatch.  I did that once with 
disastrous results.

See you in the pile-ups!

73,

Kim Elmore, N5OP
                           Kim Elmore, Ph.D.
                        University of Oklahoma
         Cooperative Institute for Mesoscale Meteorological Studies
"All of weather is divided into three parts: Yes, No, and Maybe. The
greatest of these is Maybe" The original Latin appears to be garbled.