bpnjensen wrote:
wrote:
dxAce wrote:
But, is it 'sucking it out' or merely propagating it somewhere else other than
that particular spot where your antenna is?
And that 'somewhere else' might not be very far away, but merely a few
wavelengths in distance.
dxAce
Michigan
USA
Before satellites carried most of the milcom they used "diversity
receivers".
Two, or more, receivers tuned to the same frequency but located some
distance apart.
The logic being that when the singal faded at one location, the other
didn't fade at the
same time. The more important a comm cicuit the more receivers spread
over a wider
area.
A friend and I played with our receivers feeding phone patches and
since we live 30
miles apart it was clear this approach was workable. With signals that
experienced
deep fades we were able to listen to nearly all of the time. Real
(commercial or
military) had AGC based voting systems to decided which signal to pass.
We ran
into issues of our audio phases shifting producing very odd sounding
"flanging"
effects.
I have often thought about trying this with receivers whose antennas
are only a few
hundred to thosand feet apart. I never have gotten around to it.
The military also used freqeuncy diversity, sending the same singal on
more then one
frequency. Kind of like listening to WWV on 5 10 and 15MHz at the same
time.
Terry
Fascinating. It sounds like a couple of antennae, maybe even on the
same property but spaced some modest distance apart, maybe a few
hundred feet, and phased into the same radio, might also be a solution
to the problem.
Anyone try this with a 50-acre lot and a phasing harness?
Bruce Jensen
Diversity reception has been a well established practice since the
early days. Hallicrafters produced a diversity receiver, which was
actually two receivers diplexed into a single audio stage, fed by
separate antennae.
May have been a bit of overkill. Separate antennae, if electically
isolated from one another, diplexed into a single input can produce
similar results: reducing selective fading before it reaches the receiver.
When I lived in Rockford, I rented a two bedroom home on a private
estate west of town. The rental property included several acres on a
hilltop, and access to the private lake on the estate.
Of course, I went antenna crazy. And using multiple antennae into the
BC-794, was able to mitigate a good deal of the selective fading
throughout most of the HF spectra.
Each antenna was connected to an RF preamp with a gain of 2-6db. The
outputs of the preamps were combined through resistive pads (for
isolation) into the RF input of the BC-794. The result was nothing
short of amazing, with fading distortions dramatically reduced, and
program listening, was quite pleasant. Even my wife was no longer
critical of SW listening.
Make no mistake, it wasn't FM quality. But it was fine wideband (when
conditions permitted) AM quality. And though there WAS some latent
fading remaining, it was, by far, less objectionable, and often barely
noticeable than a single antenna on the same receiver.
Diversity, at least in this case, is something to be implemented with
affirmative action.
