Bob AD5VJ said:
"Antennas are the same. Interested there have been no
advances in antennas..."
From the perspective of one who has come back into the VHF game after almost
40 years off the air: Many VHF yagis of old turned out to have much less gain
than people thought. Computer modeling has made a huge difference in designing
yagis that work.
I've just been looking up quagis , a yagi with quad reflector and driven
element, that has been used as an easy to build yagi for EME (moon bounce).
( http://commfaculty.fullerton.edu/woverbeck/quagi.htm) "On a hunch, the
driven element was removed and replaced with a quad-style loop. The forward
gain immediately increased from 6.4 dBd. to 9.8 dBd--a dramatic improvement for
an antenna rated by the manufacturer at 13 dBd. "
EME is a pretty stringent test for yagis; if the gain is 3 or 7 db less than
believed you're in trouble.
Maybe 2, 3 or 4 element yagis for HF worked well in the olden days. This
would make sense because it is a lot easier to optimize 2 or 3 elements than a
10 or 20 element VHF/UHF yagi.
My impression is that some of the standard wire antennas had the gain that
theory said they should have. It wasn't that hard to calculate the actual gain
of some of these antennas, as long as they were high enough up to work
properly. I still want to try a wire V beam or rhombic for EME, or variations
on wire collinears for portable VHF.
As far as I can tell, Bob is right, the construction techniques haven't
changed all that much.
--Walter K1CMF
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|