Steve Thompson wrote:
> -----Original Message-----
> From: Tom Rauch <w8ji@contesting.com>
> To: Amps reflector <amps@contesting.com>; Steve Thompson <g8gsq@qsl.net>
To: <amps@contesting.com>
> Date: 13 March 2002 09:30
> Subject: Re: [Amps] Antenna vs. amp (was: al-1200 question)
>
> >Please don't attribute any statement noise should be the same
> >regardless of directive pattern to me!
>
> I'm very sorry if I've misunderstood and/or misrepresented you. As a final
> clarification (and I'll shut up on the subject after this) - if I have two
> antennas with different directional characteristics, but having the same
> *average* gain integrated over a sphere, in an environment of uniform noise,
> what comes down the feeder is the same for both?
> >
>
> >Also ambient noise varies with direction, location, and frequency.
> >Whatever you are using, you should always hear a clear increase
> >in noise when you switch from a dummy load to the antenna while
> >using the narrowest expected filter in the most quiet direction....or
> >your system is noise figure or gain limited.
>
> Yes, my headache is starting to go away. Presumably, on the low bands one
> should add attenuation if necessary to get a modest but clear noise increase
> in order to get best dynamic range?
>
> Steve
>
>
Steve,
If both antennas have the same gain they will have the same directional
properties. One could have a sharper vertical pattern and the other a sharper
horizontal pattern though. Think about it as to how much total amount of the sky
that each antenna looks at. If they both have the same gain then they both look
at the same amount of sky.
In order to have gain in a particular direction you must give up something in
another direction. No free lunch here.
As you increase the gain in the direction of a wanted signal the antenna
increases the strength of the signal and the strength of the noise from that
direction also. But because the antenna is also decreasing the amount of noise
from other directions at the same time the total noise power verses the signal
reaching the receiver is reduced.
73
Gary K4FMX
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