[Ground-station] Amateur Radio in Space - presentations coming up at DEFCON, Goddard, ESA, etc.

Douglas Quagliana dquagliana at gmail.com
Sun Jun 24 19:29:13 EDT 2018


Michelle asks:
> What are the most important talking points? What should we be fighting
for? That's what I want to capture and present.

You asked.  Here are my rants and ramblings. This applies especially to
satellites with telemetry signals in the amateur radio bands, but some of
it is applicable anytime the satellite designer wants to leverage ground
stations such as amateurs or the SATNOGs community or others.

-Do something in the satellite or on the downlink that is interesting and
beneficial to radio amateurs at some level if you are using amateur radio
frequencies. You will attract more listeners and more ground stations if
there is something interesting and/or unique about your satellite, its
orbit, its downlink, and/or its telemetry. Perhaps it carries an amateur
radio transponder or a new kind of transponder to test "digipeating" a new
modulation method, or the downlink tries out a new forward error correction
scheme (not just a different polynomial, but a whole new method). Please
note that if the satellite includes an amateur radio transponder that it
doesn't have to be continuously on, and doesn't have to run "high" power
for it to be "interesting" to radio amateurs.  A
fraction-of-a-watt-weekend-only transponder would be interesting to a great
many amateur radio operators worldwide. Taking some part of the
already-published Fox satellite design and tweaking or changing it to
something else would be interesting. Doing some kind of new/different
ionosphere/propagation experiment on one of the lesser used Amateur
Satellite Service bands might be interesting. Running a beacon with varying
stepped-downward power levels on a lesser populated satellite bands (not
145MHz, not 70cm) could be interesting (see "14.1 MHz NCDXF/IARU
International Beacon Network" for the stepped-down-RF-power details, and
check the complete list of bands for downlinks in the Amateur Satellite
Service for the other not-2m-not-70cm list of bands).

-Do consider putting all of your downlinks on some frequencies other than
in the two meters or seventy centimeters bands. There are other Amateur
Satellite Service bands and other completely non-amateur bands that might
be better suited to your satellite.

-Do use your downlink as efficiently as possible. Do use forward error
correction on your main data downlink. Please. Do NOT use packet radio 1200
baud AFSK AX.25 packet radio over FM without any FEC for your downlink.
Yes, there are many stations that might receive 1200 baud AFKS AX.25 packet
radio, but for a given power output you'll get more data bits to the ground
if you include forward error correction on your downlink. You don't have to
invent a new FEC scheme, you can copy someone else's FEC scheme (Google is
your friend. Here's some hints: Voyager, various Mars mission by NASA,
Cassini, New Horizons, AO-40, ARISSat-1, FUNCube, Fox-1, interleaver,
Viterbi, Reed-Solomon, turbo codes, FX.25, LDPC, Phil Karn). Now, that
being said, short bursts of unmodulated carrier (less than one second)
could be useful for doing Doppler measurements from the ground especially
if you have an interesting or decaying orbit or if you have any propulsion
that changes the orbit. ("What is the new orbit?" is an interesting
question.) They also help out certain demodulators (e.g. Costas loop and
DSP modems). Morse code (CW) and digitized voice telemetry signals can be
used as one way to attract younger students to your signals if education is
one of your goals, but use something with FEC for the main data downlink.
Please.

-Don't be a "beepsat" that transmits some unknown kind of signal and nobody
knows what it says or what it means or what the format of the signal is.
Don't use a proprietary hardware modem whose proprietary signals can *ONLY*
only be demodulated and decoded by buying one of those modems from the
manufacturer.

-Do publish the details on how to demodulate your telemetry downlink
signals. "Demodulate" here means converting the radio signal into sounds
for the ears or ones-and-zeros for the computers. Better yet, provide a
sample executable program for Windows and Linux along with open sourced
source code that shows how to demodulate your downlink signals into a data
frame/packet. This includes publishing the modulation method and all the
details (for example, "9600 baud G3RUH modulated AX.25 HDLC and this
scrambler polynomial....") as well as the forward error correction you are
using (for example, rate=1/2, k=7 and which polynomial you are using) and
the data format (which bytes are what values, e.g. byte 17 is the X+ solar
panel voltage, and what the values mean, how to go from the raw values sent
in the telemetry value, for example, 94, back to the actual measurement in,
for example, volts). Just saying the bitrate (e.g. "9600 baud") really
isn't good enough and might cause some people to assume that they have the
necessary hardware/equipment/modems to receive the signals when really they
don't.  The more information you provide, the more stations will be likely
to receive your signals correctly.

-Do provide multiple sample recordings of your downlink signal (not just
one recording, and more recordings are better!) so that interested ground
stations can test their equipment/setup and so that people will know what
your downlink signal sounds like. Make the recording as a raw WAVE file,
not an MP3 file. Even if you use an established modulation method and FEC,
you should still create the recording of the satellite's signals so that
people can see actual valid decoded telemetry data and verify that it
demodulates and decodes correctly when received at their ground station
with their equipment. ("Nine hundred and twelve amps" from that solar
panel? Really? There's a problem somewhere. It will take that new
groundstation either that one recording, or it could take a over a dozen
actual LEO satellite passes over multiple weekends for that groundstation
to troubleshoot, debug, and fix the problem. Chances are good that the
groundstation will give up if they can't get their equipment/station to
receive your signals. Recordings will help get stations online and
receiving faster, perhaps even on day one after launch).

-Do let everyone know if your signals have some sort of temporal or spacial
restrictions, for example, the downlink will only be on when commanded on
by the command station(s), or the downlink will only be active on a
particular schedule (for example, only on Wednesdays), or the downlink will
only be active over a particular country (this is especially relevant when
that country is on the other side of the planet from the
reader/potential-groundstation). An unchanging schedule or infrequently
changing schedule is better than a continuously changing schedule. People
need to be able to plan their free time around the satellite passes when
the downlink will be on.  If there's a changing schedule, publish it on a
website where everyone can see it ahead of time (in order for them to plan
their free time before the day of the passes). In addition, if the downlink
is not continuous, that is, if the satellite only sends down telemetry data
once every N seconds (or every N minutes) then consider using a short
leading burst of low power unmodulated carrier. (I suppose this could be
longer than one second if you expect people to be spinning a tuning dial by
hand.) This could be less than a second, and a subsecond burst of
unmodulated carrier will really help the digital signal processing
programmers writing the software modems to find your signal and maybe we
can use it to do orbital analysis from the Doppler. While you're at it,
also send a few dozen alternating ones and zeros (or some other unique
one-zero pattern) before the actual data. This will also help the modems
lock onto the bit clock for your data.

-Do publish information on whether your downlink signals are linearly
polarized, right-hand circularly polarized or left-hand circularly
polarized.  Do published the downlink frequencies, and if/when those
frequencies change even slightly due to the environment of space, component
aging, or whatever, then do publish the new frequencies.

-Do publish information about how much power you EXPECT to be regularly
running on the downlink. This is not the maximum amount of power that the
transmitter can produce. This number is the amount you expect will actually
be used on a regular day-to-day basis. This will help interested stations
calculate the link budget for the downlink signals and determine whether or
not they think it's worth the effort to try to receive your signals with
their equipment (or at least it will let other people do the calculations
and then tell these stations what they need to receive/demodulate/decode
your signals).

-Do publish how to DECODE your telemetry signals especially if your
downlink is in an amateur radio band.  Decoding here refers to the process
of taking the received telemetry "values" that were demodulated and
calculating "what the telemetry means."  For example, the X+ solar panel
voltage is sent down in the telemetry in byte 21 and the value in byte 21
can be converted to the actual voltage by this equation (for example,
voltage= -0.04988 + 0.012472 multiplied by the value of byte21)).  Do
document the entire data format for all of the data coming down. Where this
sometimes runs into a challenge is when there's an experiment and the
developer of the experiment doesn't want to get preemptively "scooped" by
someone else analyzing and publishing the data of THEIR experiment faster
than they can.  If you devise the experiment, of course you want to be
first to publish the results. If that's the case, perhaps in the published
paper you can name all of the ground stations that helped collect the data,
and also publish the decoding equations in your paper so that others can
reproduce your analysis and results from the raw experiment data after the
paper is published. If not, consider a downlink on a non-amateur frequency.

-Do make your raw downlinked telemetry data available online in an archive
that others can access to perform their own analysis. They'll almost
certainly give you credit for the raw data, cite your paper, and they might
come up with some surprising results. You will never know if you hoard the
data yourself.

-Do give something back to the amateur radio community.  In a perfect world
this would be an always-on high power transponder for amateur radio
operators. In reality, this will probably be something else -- access to an
onboard amateur transponder on weekends or a promise for access to an
onboard amateur radio transponder after the primary mission is completed.
Either would be really nice.  There's probably other give backs that others
can come up with.

-Do encourage participation by creating a "leaderboard" for scoring the
received telemetry per ground station. This would attract and keep some
competitive ground stations. This encourages competition and comparison for
improvement (why did the other nearby ground station get "300"
frames/packets of data today and you only got "3"? What's he got, or what
am I doing different/wrong that my results are so far off from his?)

-Do remember that if you engage the amateur radio community (for example,
access to an amateur radio transponder) that there exists a worldwide
network of amateur radio ground stations that can be leveraged. This means
that you don't have to come up with crazy schemes to downlink all the data
during just the limited passes over your own groundstation. Be mindful that
the worldwide network of amateur radio stations is far, far LESS interested
in the satellite if there's no connection to amateur radio except that it
downlinks on amateur radio frequencies. Don't be a "beepsat" that just
pollutes the band with mystery signals.

-Do get a mentor or multiple mentors with experience. Cubesats are
inherently multi-discipline undertakings. Do ask multiple experts for help
when you get stuck.  There are so many lessons that have already been
learned that you do not want to repeat. Nobody wants to see any launch
opportunity wasted (or underutilized) because a mistake or limitation was
made that could have been avoided.  Test as much as possible, then test
some more.

ok. I better just stop here....

73,
Douglas KA2UPW/5
"Stopping here... or I could write this up as a formal paper... if you've
already got an Erdos number then let's talk co-authorship. :-)



On Fri, Jun 22, 2018 at 5:18 PM, Michelle Thompson via Ground-Station <
ground-station at lists.openresearch.institute> wrote:

> I'd like to talk about a part of our message, if our talk is accepted, at
> the Open Source Cubesat Workshop at ESA in September, and other events.
>
> There's a notice of proposed rule-making for cubesats that a lot of smart
> people are working on.
>
> What I'd like to do is make sure an amateur radio point of view is heard
> at these events.
>
> My feeling is that the amateur community is at risk of being viewed as
> administrative assistants for the rapidly increasing number of industrial,
> academic, educational, and experimental missions.
>
> Because a lot of us will consent to point our antennas at the sky and
> record beacons (or, telemetry), and happily report the information back for
> what are presented as educational purposes, that we are assumed to be
> passive consumers of the communications resources put into orbit.
>
> That we are happy with this particular role.
>
> Many of us are. It's not a bad gig. But it does risk cluttering up our
> bands with one-way very low information communications that may not really
> align very well with our potential or our justification.
>
> What I'd like to articulate is the role we really want cubesat developers
> to incorporate. I want any of us to be able to speak to that, and represent
> it, and be supported with quality materials.
>
> That is, we need to promote the development of relevant, cutting edge,
> reliable communications resources that amateurs can enjoy and use, that
> also contribute to advancing the state of the art.
>
> I would like some help with creation, comment, and critique of this
> message and a refinement of the points and examples.
>
> What are the most important talking points? What should we be fighting
> for? That's what I want to capture and present.
>
> -Michelle W5NYV
>
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>
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