[amsat-bb] What influences LEO propagation?

[Bob]

Taiwan lies within the northern edge of the Equatorial Scintillation Zone
which is an area near the magnetic equator that suffers significant signal
attenuation even at VHF (and more so at UHF an up).  It is more pronounced
during periods of high solar activity.  In the past couple of weeks we have
been having some mild geomagnetic disturbances caused by coronal holes, and
more recently an earth-effective sunspot.  Normally we think in terms of HF
impacts, but it will have big impact on space communication if you are on
one side of that scintillation zone and the satellite is on the other --
forcing the signal to cross through that area.  Best I've read indicates
you can anticipate another 20 dB of signal loss on 70 cm.  That might be
the difference between a signal that sounds great and one that is below the
noise level.

As many others have stated you also have weather influences, especially on
the 70 cm band, that will happen due to what is going on in the Troposphere.

73, Bob, WB4SON

On Thu, May 9, 2019 at 4:03 AM Hans BX2ABT via AMSAT-BB <amsat-bb at amsat.org>
wrote:

> Well, I know VHF/UHF propagation and I know satellites are
> line-of-sight, but how about signals from outer space trying to traverse
> the ionosphere and atmosphere? Es makes terrestrial signals bounce back,
> but does it also make space signals bounce back into space? Or at least
> degrade them? You say "think horizontal" but space communications are
> also partly horizontal if you take low elevation into consideration. I
> feel there is more to this, but so far haven't found any info on this.
>
> 73 de Hans
>
> BX2ABT
>
>
> On 05/09/2019 05:53 AM, GEO Badger wrote:
> > Hans,
> >
> > What I believe you are really asking is what effects VHF/UHF
> > propagation. Lighting up a bird is a line of sight connection, not
> > propagation in the classic sense of bouncing off the ionosphere and
> > ground like in HF comms. But, there are atmospheric phenoms that can
> > effect VHF/UHF comms. Tropo ducting, but that is normally for
> > terrestrial comms. Same for sporadic E, which is bouncing signals off
> > of ionized clouds similar to the ionosphere propagation..Think
> > horizontal.
> >
> > Then there is weather. Whether or not you have nice weather. Rain,
> > snow, clouds and dust are a few of the things that can effect sat comms.
> >
> > ---
> > Ciao baby, catch you on the flip side.
> > GEO
> >
> > http://www.w3ab.org
> >
> > Time flies like an arrow, fruit flies like a banana.
> >
> >
> > On Wednesday, May 8, 2019, 7:12:57 AM PDT, Hans BX2ABT via AMSAT-BB
> > <amsat-bb at amsat.org> wrote:
> >
> >
> > The last couple of days the Fox birds haven't been coming in as well as
> > before. Signal strengths are down, fading has increased and it is almost
> > impossible for me to open them. Now the sporadic E season also has
> > kicked off in the last few days, with increased activity here in east
> > Asia. Is this a coincidence or do the two have a connection? And are
> > there other factors that influence LEO propagation? I know satellite
> > tumbling is one factor that causes fades, but are there also ionospheric
> > or atmospheric influences? Thanks for the insight. 73 de Hans (BX2ABT)
> > _______________________________________________
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> _______________________________________________
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