"N4LQ" wrote in message ...
Then how come it doesn't give us 20db of forward gain? I mean, we blocked
20db off the back and applied it to the front and we still only have 5db
of
forward gain. Where did the extra 15db go?

Well... you won't handle it like that. dB aren't preserved in this
fashion. Power is...

The balloon analogy it good. Poke it "in" at one point so there is NO
radiation in that direction. The signal in the "poked-in" direction will be
really low or zero or MANY MANY MANY dB down...hundreds.


However, try this as another way to see it:

Imagine an antenna that radiates equally well in all directions AROUND the
antenna like an ideal vertical. It will have SOME signal strength in all
directions, which is the same.

Now, lets imagine another antenna (more complex and let's ignore how) which
only radiated HALF way around, but equally distributed, just like before.
That is, it cuts off all radiation to one side as though it was cut with a
knife -- and re-distributes the "cut-off power to the "good" half.
Nothing to the "bad" half -- everything to the "good" half.

The good half just went up 3dB, right ... twice the power.

The bad half went to zero. or infinity dB.

You don't conserve dB.

Help ???

--
Steve N, K,9;d, c. i My email has no u's.