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Old July 4th 07, 08:23 PM posted to rec.radio.amateur.antenna,alt.tv.tech.hdtv
Rick Frazier Rick Frazier is offline
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First recorded activity by RadioBanter: Jul 2006
Posts: 45
Default Front-to-back ratio for UHF antenna

Bishoop wrote:
snip

10 or 12 db of forward gain means your recieved signal is about 10 to 16
times as strong as a dipole hanging in the air. If you interpret the
negative number as the amount the signal is down from the forward gain,
the numbers given (9 to 17db) would indicate reception off the back side
would be somewhere near a dipole in open space (1 db net) to -5db (about
1/3 of the signal of a dipole) pickup from the back. I have used aluminum
sheet (tested prior with aluminum foil) tied to the mesh to completely
block reception from the back (a near infinite front to back ratio) in an
extreme case where I had significant multipath reflections coming in from
the back. It really cleaned things up. In your case you may not need to
go to this rather severe step.



snip

Good luck!
--Rick AH7H



10 or 12db of forward gain goes NOT equal 10 "times" the received signal
strength.


OK, so it's semantics.
a 3 3db positive change is a doubling of "power", which I relate to
signal strength on reception, hence my use of the term above.
3db ix 2x power
6db is 4x power
9db is 8x power
10db is essentially 10x power.... (and a generally accepted
approximation).

Given the nebulous measurement methods used, stating that 10-12db of an
antenna gain is nearly the same isn't that far off, assuming the stated
10-12db is even remotely accurate to begin with....

--Rick AH7H