That's a good point regarding design tradeoffs. Even if the downward lobes
are minimized in a free space design, what happens to the pattern in the
real world when there is ground and perhaps other antennas beneath the Yagi?
John KK9A
Brian Beezley k6sti wrote:
Everything else equal, yes. But it never is.
Yagi optimization is a trade-off between forward gain, the radiation
pattern, and SWR bandwidth. If the design is optimal, you can't improve
one objective without degrading another. Constraining the elevation
pattern to reject local noise will necessarily lower forward gain or
worsen SWR bandwidth. It may degrade the azimuth pattern as well.
I used to think that the term "low noise" Yagi was just marketing BS.
But I can see how constraining lobes that point toward ground ought to
reduce the level from noise sources there. The question is, how much
gain does it cost? How much do SWR bandwidth and the azimuth pattern worsen?
It may well be that for a noisy location the receive improvement is
worth the cost in gain and SWR bandwidth. But be clear-headed about it.
It won't come for free.
Brian
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|