Really? Please explain.
I ask because Rick DJ0IP and I have both spent considerable time
researching and building various OCF dipoles to build multiple-band
antennas which do not depend (or which depend less) on a tuner or
matchbox than other designs (e.g., a G5RV).
While I have yet to discover the Holy Grail of multi band antennas, the
articles I read do not mention the limitations your cite. I am not
arguing with you - I am just curious to know more, mindful of the
paucity of other references thereto.
I took care to employ a substantial, heavy duty 4:1 balun specifically
designed for the precise feed point offset I used - which is at the
25/75% position, and not at the usual 33/67% position - and this
provides very low SWR on 40m and 20m and also allows operation on 15
meters, which is usually not possible with traditional OCF designs. My
research and measurements indicate feed point impedance is approx 200
ohms, substantially lower than the usual 300 ohm figure typically
realized at the traditional 23/67% offset.
The balun was designed to both transform impedance and block feed line
radiation as a choke to minimize feed line radiation - not because I
thought there would be more than a typical dipole, but just in case.
Thus, I ask for an additional gloss on your comment, because I cannot
imagine how or why one would expect an OCF dipole to exhibit more feed
radiation than it always has. That is a curious concept. I also
cannot imagine it would be more susceptible to common mode noise than a
regular coax-fed dipole. Ergo, pray tell more.
Thanks!
------------------- K8JHR --------------------
On 7/9/2013 2:21 AM, Jim Brown wrote:
MANY years ago, when the world was much quieter, and when homes were not
full of entertainment equipment with Pin One Problems, OCF antennas were
a very good idea. That was then, and now is now. And NOW they are a BAD
idea.
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