[amsat-bb] Link budgets for upcoming HEO/GEO sats
jbarbre at xmission.com
Sat Apr 9 22:54:38 UTC 2016
Thanks John for your responses. How much power is needed to drive the
"drone" linears? Will a HackRF provide enough power to run one?
Anyone working on a mount/rotator specifically designed for these
On 4/9/2016 3:34 PM, John Toscano wrote:
> Estimates suggest aiming for 8 watts of RF and a re-purposed
> 3-foot-diameter satellite TV dish to be able to get into the bird. It
> would be nice if only 3 - 4 watts were enough to do the job, because
> there are inexpensive 3 - 4 watt linear amplifiers designed for First
> Person Video on radio-controlled "drone" aircraft like this:
> So, time will tell. It is possible that with a slower digital
> transmission rate the bird might hear well enough for the lesser
> power. I expect I will try one of these low-power amps, and might
> even consider driving a pair of them into an appropriate combiner to
> get twice the power if one by itself does not make the grade. They are
> small and light, but would require protection from weather. On the
> other hand, I should have 10 watts available if I need it, once I
> perform these modification on a much bigger and heavier surplus power
> (In fact, I have two of these beasts awaiting modification. I think
> they are much too large and heavy for my tripod-mounted rover station,
> but one of them might be doable on a fixed station.)
> It would be hard to equal the gain of a dish by using a helix. Once
> upon a time, I thought that the helix was the greatest antenna in
> existence, just make it longer and longer to get outrageous amounts of
> gain. But the more I investigated the less excited I got about
> building a humongous helix antenna. (In fact, at one point, I was
> dreaming about a 2x2 quad array of helices of great length, but I
> never actually attempted to build one.) On the other hand, I have been
> amazed by the ability of a scrap-heap satellite TV dish (less than 3
> feet in diameter) and a couple of watts of power to make terrestrial
> 10 GHz SSB QSO's over distances of well over 100 Km, at least when I
> stopped using a dish that was bent like a Pringles Potato Chip,
> causing it to lose 10-20 db of its gain! I expect even greater things
> when an un-damaged dish is pointed up into the sky, away from trees
> and hills!
> For the 10 GHz downlink, a possible low-cost scenario might work out
> to be a direct-to-home satellite TV dish of approximately one meter in
> diameter, and a PLL-based LNBF, which would mix the 10.5 GHz satellite
> signal down to the 600 MHz or so range, and the receiving that with
> some sort of SDR, possibly even a RTL-SDR USB dongle, though perhaps a
> better SDR might be required. The downlink is going to be DVB-S2x
> which is NOT the native format of the inexpensive USB dongles. DVB-S2x
> requires a bit of computation ability on the computer controlling the
> SDR, especially if the VLSNR (Very Low Signal to Noise Ratio)
> extensions are needed. It is also possible that we can find (and
> suitably modify) an inexpensive direct-to-home satellite TV receiver.
> AMSAT also expects to have a familiar USA company building complete
> ground station transceivers, but those will likely command a bit of a
> (well-deserved) premium price. We are actively pursuing a lot of
> different choices, so stay tuned!
> From what I have heard, the bird will be in a geosynchronous orbit,
> NOT a geostationary orbit, so periodic dish re-positioning of some
> sort will be necessary. Since the primary payload onto which we get to
> piggyback is owned by a government agency that likes to keep secrets,
> an exact proposed orbit is not widely discussed, if at all. So it is
> hard (for me, at least) to give more specifics at this time. You won't
> need the horizon-to-zenith-to-horizon pointing ability needed to chase
> a satellite in Low Earth Orbit, but some positioning in both azimuth
> and elevation will be needed. High precision will be more valuable
> than a wide range of pointing directions. In other words, being able
> to tweak the position by a degree at a time to fine-tune the pointing
> would be more helpful than being able to move the dish by 30 or 40
> degrees. I wish I could be more specific, but I can't at this time. On
> the other hand, one of the other projects in the works is the
> NASA-sponsored CubeQuest Challenge, and for that bird you would need
> to be able to point at any part of the sky where you observe the moon,
> since the package is going to be headed for lunar orbit! We are trying
> to make these two birds compatible with the same ground station equipment.
> Sorry for the vagueness, but I hope it helps a little bit.
> 73 de W0JT/5, EL09vu
> On Sat, Apr 9, 2016 at 12:42 PM, Jim Barbre <jbarbre at xmission.com
> <mailto:jbarbre at xmission.com>> wrote:
> Hi all,
> Given that people are currently working on groundstations for
> the upcoming HEO/GEO sats, I am in hopes that at least some of the
> following questions can be answered.
> What kind of power will be required on the 5GHz uplink?
> Does anyone currently make a linear amp or upconverter that can be
> mounted at the antenna for the 5GHz uplink?
> Will I be able to use a helix antenna on the uplink or will I be
> limited to using a dish?
> Same question with regards to antenna usage for 10GHz downlink.
> What size dish?
> With AO-10 and AO-13 I could point my antennas at the satellite
> and not have to move them for an hour or longer. These new sats
> will be using microwave frequencies. What kind of realistic
> expectation do I have of being able to point a dish at the
> satellite before having to tweak it? Otherwise said, will a
> rotator be absolutely necessary?
> Thanks for the info. Looking forward to working the next
> generation of HEO/GEO sats.
> Jim Barbre
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