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RE: Dish aiming



Someone wrote...

> While it is very true that increased gain = decreased beamwidth, increased 
> gain also means increased link margin. The added gain of the larger antenna 
> allows it to be off pointed more than if every dB of gain was required. 
> This is the reason those darn little DSS antennas are so difficult to 
> align. As a rule, the pointing accuracy needs to be better than the 3 dB 
> beamwidth of the antenna. Some amount of inaccuracy can be compensated for 
> by adding system margin.

I think This is true only  within the 3dB beamwidth of the antenna.  But
when we are talking high gain, then that is the only thing to talk about.
If the 3 dB beamwidth is 4 degrees (+/- 2), then the pattern nulls are at
+/- 4 degrees.  These nulls are probably 30-50 dB deep.  The first set of
sidelobes are probably 20 dB down or more.  SO there is no way that
increased gain ever helps in off-pointing errors.

Remember, gain comes from loss everywhere else.  So for every dB of more
gain you have, you have that much less everywhere else...  Thus, in
general, you never want more gain than you need, or you have to improve
your tracking accuracy as well...  The laws of physics are hard to
break...

bob


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