[amsat-bb] Link budgets for upcoming HEO/GEO sats
n1jez at burlingtontelecom.net
Sun Apr 10 11:14:44 UTC 2016
Preliminary tests on the amp show ~ 11.5 dBm in will give 3.5 watts out.
That is after a mod to remove an internal pad. Testing done at 5760 MHz.
From the HackRF specs, you would need 10-20 dB of gain to drive the amp
as output between 4000-6000 MHz is -10 to 0 dBm. I'd probably use a
simple MMIC amp for starters.
I hope to test the system once my amp arrives in the next week or so.
On 4/9/2016 6:54 PM, Jim Barbre wrote:
> 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
>> 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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