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 satellites?
73 Jim KB7YSY
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: http://www.ebay.com/itm/262249565979?_trksid=p2057872.m2749.l2649&ssPage...
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 amplifier: http://www.g4fre.com/avantekpa.htm (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@xmission.com mailto:jbarbre@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. 73 Jim Barbre KB7YSY _______________________________________________ Sent via AMSAT-BB@amsat.org <mailto:AMSAT-BB@amsat.org>. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb