On Sun, 14 Aug 2011 19:46:34 -0700, Jeff Liebermann
wrote:

On Sun, 14 Aug 2011 23:27:33 +0200, Helmut Wabnig [email protected] ---
-.dotat wrote:

Want one?

Not really, since I can't do anything to fix the alleged problem.

4nec2 from time to time destroys it's saved antenna files.
Just lost another 2 hours of work.

Nobody does backups until after they have lost data. I've been using
4NEC2 for at least 7 years and have never lost a file. Well, I have
accidentally overwritten a file, but that was my fault. When I tinker
with antennas, I save multiple versions of the same design with the
version number appended as in file001.nec. This way, if I make a
horrible mistake, I can go back to a previous version and try again.

Now I understand why it's free.
Can't charge money for bugs.

Well, that why we have alternatives to 4NEC2 and why I don't charge
for my free advice:
http://www.smeter.net/antennas/mmana.php
http://www.eznec.com
http://www.nittany-scientific.com
http://www.hamradiosecrets.com/antenna-design-software.html
http://www.si-list.net/swindex.html (old but still useful)


###########"Backup, you say it". ###########

When optimizing for F/B also 4nec2 results in a too short driven
element, same as YAGICAD, they obviously use the same formula,
(a long two-liner) from literature.
I actually built antennas following that prescription,
and they do not work without additional corrections,
e.g. a very long hair-pin match.



Imagine a 3 element 2 meter yagi,

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Something is wrong here with the capacitive driven element.
Now I am having a hard time, because I want to find out in
what differs a gain optimized vs a F/B optimized antenna
and it is questionable whether that can be done with software.
Have not tried other programs yet.

http://imageshack.us/photo/my-images/837/snc14096a.jpg/

The Front to Back ratio is very frequency dependent
http://imageshack.us/photo/my-images/220/fbratio.jpg/
(Without the hair pin match)
http://img5.imageshack.us/img5/3479/snc14112hairpin.jpg

Therefore I put the driver on a slider
http://img841.imageshack.us/img841/8...14097small.jpg
which allows to adjust the working frequency of the antenna
over a 10 MHz range on 2 meters. Adjust for minimum reception
from the back and the antenna is optimized for that frequency.

Now I want to collect a list of recipes which allow to build the
antenna without having to tweak it on the antenna analyzer.

A similar design once was offered by DIAMOND MAY1000
http://www.rfparts.com/diamond/MAY1000.html
Look at the frequency chart
http://www.rfparts.com/diamond/pdfdo...dj%20Chart.pdf
With that antenna one could adjust the element lengths *and*
the distance between the elements, which is crucial for the F/B ratio.

A Yagi with fixed element positions can only be used for 1 frequency
(within a very small range) and therefore may be impractical
in many situations. The CEBIK tape measure antenna with their
water-pipe construction could be easily modified with a moveable
center element.
http://www.g6hoq.com/documents/2m%20...structions.pdf
Above line as shortlink: http://tinyurl.com/3m5p5nq


w.