--- Sarcasm Button ON ---
Well... I am all corn-fused.
Last year, I researched the heck out of OCF antennas, reading many
articles, web pages, ARRL Handbook, ARRL Antenna Book, and more. I
discussed my notions with a well known commercial balun designer. I
wanted to build a 40m OCFD that included 15m, which is usually out of
bounds, and I wanted to lower the expected impedance from the typical
guess of 300 ohms to around 200 ohms.
So, following Rick's advice to eschew modeling programs, and build,
test, and measure what happens in real life, instead... I cut my OCF
dipole with an unusual 75 / 25% offset (rather than the typical 33/65%
offset) -- And VOILA... it worked, giving low SWR on 40m and 20m, and
around 3.5 - 3.8 SWR on 15m and 10m. Unfortunately, 6m went up higher
than 5:1 SWR... but my antenna tested out in place as planned! Eureka!
And, so I thought I was being a good ham by experimenting like this.
But now, Rick says I gotta have more proof... that I cannot trust my
expensive RigExpert analyzer, or the cheaper one I borrowed from Chuck,
and says I need "more proof" my antenna works as claimed. Sheesh...
NOW, he says his computer modeling belies my actual measurements, and
also accused me of having "feed line radiation" which (it is suggested)
cannot possibly be managed by the 4:1 balun and choke I installed.
Oh dear... so I guess I failed, after all.
So... I got one of the local rabble (who is employed full time as a
commercial radio and network systems engineer engaged in business
building and installing commercial radio equipment, including towers and
antennas) to check my installation to determine if I do, indeed, suffer
from the dreaded
latent-hidden-symptoms-of-yet-undiscovered-transmission-line-radiation,
and he gives my station a clean bill of health.
So. What should I conclude? Should I assume he and his test equipment
are incompetent? Or can rest easy thinking my simple OCF dipole works
as it should?
A retired college electronics professor and radio design engineer (who
used to build stuff for NASA, the Air Force, and Lear Jets,) thinks I
should be OK to use it as is ... but Rick says I place too much faith in
what he says, and demands more proof, saying the evidence from my
antenna analyzer is inadmissible, cause his modeling software says the
SWR cannot be as low as it says.
And yet, I am not alone in thinking this antenna works: There is a web
page charting the results from several experiments where different feed
points were tested:
http://hamwaves.com/cl-ocfd/survey.html
Darn. I was sorta hoping someone would compliment me for being a good
ham by
1) doing the research,
2) daring to employ an "unusual" design
(i.e., moving the feed point offset)
to enable 15m on a 40m OCFD,
3) building it, myself, and which
4) appears to work according to plan.
So, how did I go so far wrong? ;-)
Happy days, gentlemen !!! ;-)
The Take Away:
There may be a point where too many
cooks spoil the broth, and too much
science can spoil an other wise good
antenna project.
;-)
Just MY take, ... your mileage may vary.
--------------- K8JHR ------------------
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|