[amsat-bb] What influences LEO propagation?

Fri May 10 16:21:58 UTC 2019

Hans,

We get two different effects from the tumbling. First the polarization
changes as the antennae rotate because they have linear polarization. You
can minimize that impact if you have circular polarization on the ground.
Second the antenna pattern is rotating and it has nulls which may pass over
your station. Depending on the speed of rotation they might prevent you
opening the transponder. They definitely impact telemetry reception.

One thing to note is if telemetry is being received. If you can see the
RSSI and there are no other stations in the footprint then you can
sometimes see the received signal strength from your station. Have FoxTelem
plot the graph real time and see what effect transmitting has.  If the sat
is receiving you but not being opened then perhaps the tone is not being
decoded correctly due to peaks and nulls from the rotation.

73
Chris

On Fri, May 10, 2019, 08:20 Hans BX2ABT via AMSAT-BB <amsat-bb at amsat.org>
wrote:

> Wow, first time I've heard about this and it explains very well what
> I've been seeing lately. Especially the deep, fast fading on many of the
> AO-91/92/95 passes. I found this page that explains the basics of
> equatorial scintillation: https://www.sws.bom.gov.au/Satellite/6/3.
> Fascinating stuff, but on the other hand it makes my ham life in Taiwan
> a bit more complicated. Also found this white paper, but I haven't read
> it yet:
>
> http://web.stanford.edu/group/scpnt/gpslab/website_files/sbas-ion_wg/sbas_iono_scintillations_white_paper.pdf.
>
> What I do get is that a lot of it is about scintillation on GPS
> frequencies and the L-band. The bands we use are a lot lower, but still
> suffer some influence.
>
> Thank you Bob, lots to read this weekend.
>
> Hans
>
> BX2ABT
>
>
> On 05/10/2019 01:11 AM, Bob via AMSAT-BB wrote:
> > 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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