[amsat-bb] XW-2D Returns to Life!

[Hasan al-Basri]

My pleasure, Zach.
KB7IJ and I have logged probably 1000 hours of measurements to arrive at
the "rough and dirty" approach listed and despite all the confounding
variables like:

1. Rotating Polarization
2. Faraday
3. Satellite Body Shading
4. Broken sats (Like XW-2F with it's 20 dB tumble)
etc., etc.

it became apparent that if we were running the same software, same
bandwidth (as you noted), and calibrated to a simple dummy load, we could
isolate variables quite quickly and see if what we "did" made a predictable
difference. Having the ability to record both video and audio and play back
with  announcements of the "real time' change, is quite an advantage.

Operating sats without an SDR or a 9700 is operating blindfolded. Once a
person can "see" the entire passband in full duplex in real time, a new
world of what is going on opens up. Of special importance is the ability to
see the beacon 100% of the time and adjust uplink power accordingly.

It is quite interesting to see the CAS series (4A/4B) with not only their
CW beacon, but also the Batwing PSK beacon. Seeing that beacon fade 20 dB
on one polarization and then return to full strength immediately upon
changing to another polarization is quite awakening. There are also
profound pre and post TCA (Zenith) signal strength patterns that can be
strikingly correlated to the "nature of the pass". Very Shallow, Shallow,
Medium, Overhead etc.

There are so many variables involved,  even the 3 dB worst case loss from
linear to circular does not hold ...in fact it is very rare that my 2m
EggBeater is within 3 dB of my 5 EL vertically polarized yagi. Close in
vegetation loss, ordinary obstruction loss (EB is only up 7',  Yagi up 65')
Of course at very high elevations the EB shines...but only for a very few
minutes.

Bob Bruninga hit on a great find with his Fixed Elevation of 15 degrees for
LEO birds. You can look at my pix on my qrz page and see what his approach
looks like. The performance has been phenomenal and no elevation rotor is
required. I routinely work every one of the Mode B LEO birds down to an
elevation of -0.7 degrees with that setup, and only at EL > 60 deg do I see
the EB outperforming Bob's simple suggestion.

Sats are fun for the curious. Anyone who loves satellites, get an SDR
...you will  never go back.
73, N0AN
Hasan


On Thu, Mar 5, 2020 at 1:33 PM Zach Metzinger via AMSAT-BB <
amsat-bb at amsat.org> wrote:

> On 2020-03-05 13:00, Hasan al-Basri wrote:
> > Since we were speaking of SSB SNR, the bandwidth would be similar. In
> > our cases we use 2.2 kHz. I forgot to even mention it.
> >
> > The ...and the point of the whole process was to keep it simple. The
> > more precise, the more complex and the less likely anyone is going to
> > bother.
>
> Hello Hasan,
>
> I definitely applaud your efforts to measure relative system
> performance, but I did want to make it clear to others on the list that
> there was another factor which needed to be taken into account when
> doing an apples-to-apples. This additional factor isn't too hard, when
> you understand why it matters.
>
> > Boltzman is not needed for that. We aren't doing EME. Sat ops are a
> > relatively strong signal mode. It says a lot that many receive setups
> > are performing so poorly that "rough and dirty"  (and simple) approaches
> > like I outlined can make a big difference in overall efficiency. I just
> > hope that it helps people hear better.
> > (and subsequently reduce their uplink power)
>
> I also completely agree with you on the need for fewer alligators on the
> satellites. With GOLF, where we're building bigger vehicles with larger
> orbits and footprints, excessive uplink power becomes an even bigger
> issue for more simultaneous users.
>
> That said, GOLF satellites will also incur more path loss, so getting
> LEO operators more familiar with the "down in the noise" issues will
> make for better MEO/HEO operators, too.
>
> Keep up the good work! I enjoyed your video.
>
> 73,
>
> --- Zach
> N0ZGO
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