bob wrote:
Expressed another way, is a non-resonant antenna sometimes better for
reception than a resonant antenna?


There are several possible causes here.
Probably, on the design frequency, its antenna is probably matched to 50
ohms , for good transmission. A matched antenna does not necessarily give
the best S/N for reception, and usually a mismatch does. Its hard to
calculate.

Although this can be true at VHF/UHF, where the receiver noise
dominates, it's not true at HF, where the observation was made. At HF,
external noise dominates, so the quality of impedance match makes no
difference in S/N ratio.

One filing mentions the possible change in pattern, and therefore a
possible change in S/N.
. . .

I'm certain that's the explanation (assuming it's not a mistaken
subjective observation) -- the noise is coming pedominantly from one
direction, and by tuning the antenna a pattern null was created in that
direction. Signals from other directions are then stronger than the
reduced noise.

I've often directed my 40 meter 4 square array toward the southwest to
put a null toward the U.S. Midwest and Gulf Coast, where a lot of
thunderstorms occur in the summertime. VKs jump out of the noise when I
do that. Rotatable loop receiving antennas are often used in the same
way, to null out noise coming from one direction.

Roy Lewallen, W7EL

I am not satisfied that the original poster has not made a "mistaken
subjective observation"

Don't think we have heard from him on this aspect.

--
Caveat Lector



"Roy Lewallen" wrote in message
...
bob wrote:
Expressed another way, is a non-resonant antenna sometimes better for
reception than a resonant antenna?


There are several possible causes here.
Probably, on the design frequency, its antenna is probably matched to 50
ohms , for good transmission. A matched antenna does not necessarily give
the best S/N for reception, and usually a mismatch does. Its hard to
calculate.

Although this can be true at VHF/UHF, where the receiver noise dominates,
it's not true at HF, where the observation was made. At HF, external noise
dominates, so the quality of impedance match makes no difference in S/N
ratio.

One filing mentions the possible change in pattern, and therefore a
possible change in S/N.
. . .

I'm certain that's the explanation (assuming it's not a mistaken
subjective observation) -- the noise is coming pedominantly from one
direction, and by tuning the antenna a pattern null was created in that
direction. Signals from other directions are then stronger than the
reduced noise.

I've often directed my 40 meter 4 square array toward the southwest to put
a null toward the U.S. Midwest and Gulf Coast, where a lot of
thunderstorms occur in the summertime. VKs jump out of the noise when I do
that. Rotatable loop receiving antennas are often used in the same way, to
null out noise coming from one direction.

Roy Lewallen, W7EL