[amsat-bb] What influences LEO propagation?
Hans BX2ABT
hans.bx2abt at msa.hinet.net
Sat May 11 13:11:45 UTC 2019
Hello Chris,
Thanks for that explanation. There are so many factors involved in
reception of satellites that it almost seem too complex. By monitoring
as much as I can there are certain patterns that are emerging. I do know
for example that mountains to the south-east from me block signals below
5 degrees and I do get a lot of RF reflected back to me from a metal
rooftop building near-by. If you take these and other local factors into
account (antenna elevation, local buildings, etc). then there are still
a lot of anomalies that take place during passes that are similar in
direction/elevation.
I'll check the RSSI thing, but earlier this week the problem was that I
couldn't even get any telemetry in. Passes that would normally yield
40-80 DUV frames netted maybe 1 or 2. I could see signal, hear it,
albeit noisy (less than 5 dB SNR), but ever so weak. The next day a
similar pass with stellar signals (SNR 30+dB). Could get in, but only
part of the pass. Then later a pass where I can work stations towards my
south, but not my north, while my south is always more difficult to
work. It's almost like shortwave propagation, where "life's like a box
of chocolates." Are spin rates of birds like AO-91/92/95 known?
And...are there more parameters in FoxTelem which you can check to study
variations in signal propagation? Cheers for any hints. 73
Hans
BX2ABT
P.S. Chris, did you get the zip with 1.0.6. data I sent you Monday? I
sent it before, but it came back, then sent it again. Hope we don't have
email troubles, again.
On 05/11/2019 12:21 AM, Chris Thompson wrote:
> 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 <mailto: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 <mailto: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 <mailto: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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