I can't post from where I'm at... up in VT. Pse re-post this for me?
First, you're right about the Bell Labs work of the 30's. I read the
original papers, in proceedings of
the IRE, in the engineering library when I was in college.
Secondly, I was reminded of an IRE paper of 1934 or 35, where Bell Labs
did work on arrival angle
and polarization studies.
Thirdly, I can't provide a reference on arrival polarization tending
toward the horizontal, without
digging through my library at home. But based on a conversation with
K2BMI, on the drive to VT
yesterday, the observation was made that the polarization tends to be
elliptical. And it tends to
have multiple paths, as well. As a result, you can get signal arriving
at, say 20 degrees above the
horizon, and at 8 degrees above the horizon, at the same time. It may
slowly vary in polarity and
phase, and both paths may vary differently. The short form result of
this complex soup is that
dual diversity compensates for a lot of dynamic phase and polarity
variations.
Which raises another question: Has anyone tried diversity receive on
stacks? With what
results?
Jim/N2EA
On Apr 11, 2009, at 6:58 AM, Michael Keane K1MK wrote:
> On 4/10/2009 11:08 AM, jim Jarvis wrote:
>
>> accepted the literature which said
>> that all signals arrived horizontally polarized.
>
> I can't recall ever having seen this bit of folklore written down
> anywhere. Does anyone know a source? Just my curiosity.
>
> FWIW, the phenomenon of "skywave" fading was first studied by Bell
> Labs, RCA, NBS, etc., in the early days of shortwave radio, the 1920s.
> They pretty much got it right back then :-)
>
>> This morning, I learned that it may be
>> polarization that is the principal
>> variable.
>
> And at times when multi-path (spread) propagation is present, that can
> be a significant source of fading.
>
> Very broadly speaking, near the MUF when only a single, stable
> propagation path is present, polarization fading will be the dominant
> cause of fading. Below the MUF or when the ionosphere is disturbed,
> then multi-path effects are significant. Far enough below the MUF,
> where absorption limits the number of alternate paths, polarization
> fading once again becomes important.
>
> To counter polarization fading one would like to have an ability to
> switch between antennas with orthogonal polarizations. To counter
> multi-path fading one would like to have an ability to switch between
> physically separated antennas, i.e. spatial diversity. To counter
> ionospheric propagation mode switching, e.g single-hop F2 vs.
> double-hop F2 vs. single-hop Es, etc., one would like to an ability to
> switch between antennas emphasizing different elevation angles.
>
> Once again the bottom line is, as it has always been, having more
> antennas from which to choose is better than having fewer.
>
> Oh, and those antennas are on towers. :-)
>
> 73,
> Mike K1MK
Let's MAKE it a great day!
Jim Jarvis, MBA, President
The Morse Group, LLC
732 548 5573 office 908 410 9130 cell
www.themorsegroup.net
Leadership and Supervisory Development * Strategic Planning * Corporate
Coaching
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