[amsat-bb] Source for 3" (76mm) pipe for dish mount?
zleffke at vt.edu
Mon May 9 23:26:46 UTC 2016
DISCLAIMER: Personally, I think its relevant because it has to do with
increasing your skill in the art of radio and satellite communications.
More specifically, I think the skills needed (building/finding LNAs,
building antennas, modem development, tuning for doppler, link budgets,
etc.) are directly related to the Amateur Satellite hobby even if your
practicing 'out of band' relative to what folks might be used to on this
list. Case in point, AMSAT's nasabare.txt TLEs include spacecraft (such
as the NOAA POES birds) that have no Amateur Radio equipment on board,
but they do it because people tend to have overlapping hobbies. So I'm
posting my response to the list, but if others disagree and prefer the
conversation be moved off list I'm more than happy to comply.
I too have an interest in the GOES birds, inmarsat, and basically
anything from airplanes (ADSB), to ships (AIS), to NWS high altitude
balloons, to LEO birds, to MEO/HEO birds, to GEO birds. (basically
'other' stuff that is not necessarily ham radio specific, but in the
Source for cheap-ish preamps/LNAS: minicircuits.com
Basically for LNAs, I found that minicircuits.com has a number of
'decent' low noise amplifiers that can be used for receiving these types
of signals. they usually cost anywhere from 30-75 bucks (usually around
50) depending on what you are trying to accomplish and the individual
specs for the band of interest, and are typically wideband enough to
cover multiple non-contiguous chunks of spectrum (Like 1550 MHz signals
and 1691 MHz signals in L-Band). They also sell pretty decent (And
cheapish, maybe $20) bandpass filters that may be of interest if you are
in a high QRM environment.
For L-Band (Inmarsat, Iridium, etc) I made a bi-quad feed that covers
Inmarsat and the SARSAT frequencies around 1550 MHz. I have played
around similarly with 0.75m to 1.2m primestar type offset antennas
mainly for the GEO birds. The biquad plus a 0.75m offset reflector plus
minicircuits amp plus RTL-SDR plus GNU Radio was all that was needed to
observe/capture recordings of the Inmarsat 'Fleet Safety Net' broadcast
service (an open and public service, not private communications).
Helicals are also good choices because they are simple to build and
inherently wideband (forgiving of manufacturing error).
My most recent interest is in the NOAA POES SARSAT transponders (Same
birds that carry the 137 MHz APT transmitters). Distress beacons
transmit around 406 MHz up to the birds (EPIRBs for boats, ELTs for
Planes, PLBs for hikers). They rebroadcast that down at L-Band. They
have a bent pipe transponder that simply rebroadcasts the beacon as well
as a digital downlink that contains information about the beacons from
the onboard processing systems. Same transmitters/data processors exist
on the GOES birds as well. Also the system and the spec is VERY well
documented and public (google COSPAS-SARSAT and look around for the
"technical documents" section). I'm trying to develop a graduate level
(or 'really good undergraduate' level) student project (maybe in the SDR
course as a class project?) to code up some open source out-of-tree
modules for GNU Radio to do the full demodulation/FEC decoding/data
presentation for this.
Similarly 1690-ish MHz is an interesting band because there are three
'targets of interest' to me. The NOAA POES (15, 17, 18) and NOAA GOES
birds all transmit HRPT in this band. Additionally, the NWS high
altitude balloons that fly twice a day from the 50-ish (no sure about
the count there, but theres a lot of 'em) locations around the country
also operate close to this band. So one antenna/preamp/RTL-SDR
combination could potentially net you access to some GEO birds, LEO
Birds, and HABs. (We're fortunate in Blacksburg to have an NWS station
about a quarter mile from my office at the airport that launches the
balloons, others' mileage may vary on that one).
For both the NOAA balloons (more specifically Lockheed Martin - Sippican
Radiosondes, LMS-6s) and the Inmarsat Fleet Safety Net, there are
Windows decoders that give you free 30-day trial, then you have to pay.
Again, I'm hoping to find a way to turn this into an SDR class project
(or satcom, or summer REU program, or however I can pull it off) to have
students gain experience developing modems for this. My intent is to
develop free and open source GNU Radio modules for these decoders (Train
ATCS is also on the list, but not relevant to this discussion) and then
post them on github for others to use with GNU Radio.
I'd be happy to swap notes with you (or anyone else on the list)
concerning these systems. I've done a lot of legwork compiling the
various sources for the specs, frequencies, etc. for these systems and
would be happy to send links/docs your way. And again, even though I
think its relevant I could understand if others on the list don't agree
and I'd be happy to move the conversation off list if anyone objects.
Happy signal hunting!
Ted & Karyn Hume Center for National Security & Technology
Virginia Polytechnic Institute & State University
Work Phone: 540-231-4174
Cell Phone: 540-808-6305
On 5/9/2016 5:54 PM, Scott wrote:
>>>> If you can supply photos of links of the actual dish we may be able
>>>> to help further.
> ... I found a pic online that looks right; it's a 1m Primestar dish.
> I cropped out just the dish - here is the link:
> ... I have previously been using an old round DirecTV dish with
> various home-made and purchased antennas to receive Inmarsat and a few
> other signals but obviously needed something larger to experiment
> further. Both Vivaldi and patch style antennas have worked well with
> the DirecTV dish. I'm not completely sure what I will do with this 1
> meter dish, but I don't have any plans for tracking at this time. A
> stationary mount will be fine.
> Having already gained some familiarity with Inmarsat signals, that is
> one option. It may very well be beyond my reach, but I would like to
> educate myself about what is available on the GOES-13 satellite as
> well. I even have a commercial FTA TV LNB to experiment with. It
> seems like the upcoming amateur satellites will require familiarity
> with more gain & higher frequencies as well, so I have a lot to learn
> LEO telemetry cubesats and the like are my main interest, but I like
> the idea of having a dish to experiment with as well. Certainly
> appreciate everyone's input!
> If satcom topics like Inmarsat & GOES-13 are not of interest on this
> mailing list, by all means please feel free to contact me directly if
> you have any pointers!
> If you are not using it in a fixed position, but for low earth orbit
> tracking on s-band, like I am, I can give more advice. I am using a
> 1.2 metre dish. In particular the modification for larger feeds,
> calibration due to offset feed and real world low earth orbit tracking
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