[amsat-bb] AO-92 fading
Mark L. Hammond
marklhammond at gmail.com
Wed Mar 28 11:44:26 UTC 2018
Stefan,
The reason I suggested using telemetry is because there is no uplink
variable to deal with. I thought the original issue was about "fading" and
why it happens. One can look at only the downlink, if interested. This
would allow somebody to study downlink fading. Of course, it doesn't touch
the uplink side of the issue...but that was rather my point.
Mark N8MH
On Tue, Mar 27, 2018 at 10:38 PM, Stefan Wagener <wageners at gmail.com> wrote:
> Thanks Steve,
>
> Great point and well thought out. Now, let me ask you a question: After you
> matched the downlink signal and position of your Arrow for maximum quieting
> and best signal, what happens when you now change the position of your
> arrow to look for best "uplink"? unless yo can keep the downlink position
> steady you will not be able to check for the uplink.. as science tells me
> one thing has to be constant for the other to be assessed...
>
> All the best,
>
> Stefan, VE4NSA
>
>
>
> On Tue, Mar 27, 2018 at 9:27 PM, Stephen E. Belter <seb at wintek.com> wrote:
>
> > Stefan,
> >
> > You are correct that you only hear the downlink, but...
> >
> > From personal experience, including operating AO-85 and AO-91 today using
> > a standard Arrow and an IC-821 (from a campground in EM87), I'm convinced
> > that I can hear my uplink polarity mismatch.
> >
> > I first adjust the polarity of my antenna (by twisting my wrist) while
> > searching for the strongest (maximum quieting) received signal. Then
> while
> > pressing the PTT, I tweak the Arrow polarity while going for maximum
> > quieting while listening to myself.
> >
> > The best sounding full-duplex signal is typically not at the same
> polarity
> > as the best received signal from someone else on the satellite, but I've
> > been able to get full quieting full-duplex. When operating full-duplex,
> I
> > think I'm hearing the results of *both* the uplink and downlink polarity
> > match.
> >
> > And that's how I 'differentiate between uplink "weakness" from downlink'
> > weakness.
> >
> > 73, Steve N9IP
> > --
> > Steve Belter, seb at wintek.com
> >
> >
> > On 3/27/18, 10:06 PM, "AMSAT-BB on behalf of Stefan Wagener" <
> > amsat-bb-bounces at amsat.org on behalf of wageners at gmail.com> wrote:
> >
> > Hi Sterling,
> >
> > That would assume you have the ability to switch between linear
> uplink
> > polarization (vertical and horizontal) and circular polarisation for
> > uplink
> > (right and left) and keep you downlink polarization on the same
> > optimized path all the time, meaning you know in advance which way
> the
> > downlink signal is the best to compensate for any uplink
> discrepancies.
> > Good luck :-)
> >
> > But hanks, good thought!
> >
> > Stefan, VE4NSA
> >
> > On Tue, Mar 27, 2018 at 8:47 PM, Sterling Coffey <kawfey at gmail.com>
> > wrote:
> >
> > > If linear polarized, if you can keep your RX/downlink antenna still
> > and
> > > you can at least hear the satellite, and rotating your TX/uplink
> > antenna
> > > results in correlated signal level changes on the RX/downlink, then
> > you've
> > > isolated it to the uplink polarization variable.
> > >
> > > On Tue, Mar 27, 2018 at 8:44 PM, Stefan Wagener <
> wageners at gmail.com>
> > > wrote:
> > >
> > >> Thanks,
> > >>
> > >> Again, even in full duplex how do you distinguish between a
> > non-matching
> > >> uplink vs non-matching downlink? You only "hear" the downlink!
> > >>
> > >> 73, Stefan VE4NSA
> > >>
> > >> On Tue, Mar 27, 2018 at 8:38 PM, Sterling Coffey <
> kawfey at gmail.com>
> > >> wrote:
> > >>
> > >>> You can hear your own signal if you have a full duplex (two
> radio)
> > >>> setup. However, it's still pretty hard to tell if you use a
> single
> > antenna
> > >>> (arrow, elk, etc) since you're changing the RX polarity while
> > you're
> > >>> changing the TX polarity too.
> > >>>
> > >>> On Tue, Mar 27, 2018 at 7:22 PM, Stefan Wagener <
> > wageners at gmail.com>
> > >>> wrote:
> > >>>
> > >>>> One of the questions I have is why one would think that the
> uplink
> > >>>> (polarization) is a problem since you only have the downlink to
> > assess
> > >>>> and
> > >>>> how would you differentiate between uplink "weakness" from
> > downlink
> > >>>> since
> > >>>> that is the only thing you hear. In addition, at least for
> > uplink, you
> > >>>> could "in principle" very quickly adjust with higher power...
> and
> > no, I
> > >>>> am
> > >>>> NOT promoting crocodile behavior (big mouth little ears)
> > >>>>
> > >>>> Stefan, VE4NSA
> > >>>>
> > >>>> On Tue, Mar 27, 2018 at 2:26 PM, Burns Fisher <burns at fisher.cc>
> > wrote:
> > >>>>
> > >>>> > If you have seen a model or picture of the Fox satellites, you
> > may
> > >>>> have
> > >>>> > noticed that some of the solar panels seem to be mounted
> > off-center.
> > >>>> This
> > >>>> > is intentional so that photons that reflect off the shiny side
> > give
> > >>>> it a
> > >>>> > tiny off-center push that spins the bird to distribute the
> heat
> > more
> > >>>> > evenly. Thus it spins faster the more time it spends in the
> > sun. In
> > >>>> > addition, when it crosses the equator, it should flip over (-Z
> > and +Z
> > >>>> > reverse sides). This is because of the passive magnetic
> > >>>> stabilization.
> > >>>> > But I'm guessing that since it is spinning, that causes it to
> > wobble.
> > >>>> >
> > >>>> > Why 92 seems worse I don't know--I can only assume it has
> > something
> > >>>> to do
> > >>>> > with the orbit. That graph that Paul posted looks very
> > different from
> > >>>> > AO-85, for example.
> > >>>> >
> > >>>> > Some RF person can correct me, but I believe that the 70cm
> > antenna
> > >>>> only
> > >>>> > uses the antenna that sticks out one side, while the 2m
> antenna
> > >>>> actually
> > >>>> > uses the antennas on both sides. Could that explain why the
> > uplink
> > >>>> has
> > >>>> > more fading than the downlink? I don't know. Something to
> > think
> > >>>> about.
> > >>>> >
> > >>>> > 73,
> > >>>> >
> > >>>> > Burns WB1FJ
> > >>>> > Fox-1 Flight Software
> > >>>> >
> > >>>> > On Tue, Mar 27, 2018 at 2:12 PM, Paul Stoetzer <n8hm at arrl.net
> >
> > wrote:
> > >>>> >
> > >>>> > > All of the Fox-1 satellites seem to spin faster or slower
> > depending
> > >>>> on
> > >>>> > > orbit illumination or other factors.
> > >>>> > >
> > >>>> > > For example, this is the +Z panel rotation on AO-92 since
> > launch.
> > >>>> > >
> > >>>> > > https://imgur.com/a/uS8TB
> > >>>> > >
> > >>>> > > Someone more well-versed in these matters can comment
> further
> > on
> > >>>> what
> > >>>> > > causes this, but it is definitely not an indication of the
> > health
> > >>>> > > status of the satellite.
> > >>>> > >
> > >>>> > > 73,
> > >>>> > >
> > >>>> > > Paul, N8HM
> > >>>> > >
> > >>>> > > On Tue, Mar 27, 2018 at 1:59 PM, Jean Marc Momple
> > >>>> > > <jean.marc.momple at gmail.com> wrote:
> > >>>> > > > Dear All,
> > >>>> > > >
> > >>>> > > > I have been experimenting with AO-92 as from its launch.
> > Some
> > >>>> > > observations:
> > >>>> > > >
> > >>>> > > > 1) The fading on this bird seems to be high and quite
> > >>>> unpredictable,
> > >>>> > > requires a lot of changes of polarization to keep the Rx
> > signal to
> > >>>> an
> > >>>> > > adequate level.
> > >>>> > > >
> > >>>> > > > 2) Seems that the fading is both on the U/V and L-mode,
> more
> > >>>> seems to
> > >>>> > me
> > >>>> > > that the uplink is more affected.
> > >>>> > > >
> > >>>> > > > 3) Telemetry seems to be quite reliable with FoxTelem in
> all
> > >>>> modes.
> > >>>> > > >
> > >>>> > > > Today, it was even worse losing the bird many times during
> > the
> > >>>> pass, it
> > >>>> > > seems that it is degrading quite quickly, hope that this is
> > not the
> > >>>> case.
> > >>>> > > >
> > >>>> > > > Just to share my observation.
> > >>>> > > >
> > >>>> > > > 73
> > >>>> > > >
> > >>>> > > >
> > >>>> > > > Jean Marc (3B8du)
> > >>>> > > >
> > >>>> > > >
> > >>>> > > > _______________________________________________
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> expressed
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--
Mark L. Hammond [N8MH]
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