[amsat-bb] What on earth (or in space...) is going on?
k3io at verizon.net
Mon Dec 28 10:00:51 UTC 2015
A related thread has been running on QRZ.com where I just posted this
> To all those who have been bewailing the fact that the microwave
> technology needed to use the P4B digital GEO satellite let me
> offer a couplke of comments. I preface this by saying I am a part
> of both the AMSAT and VT "factions:".
> All of you are making the mistake in believing that the 10 GHz
> downlink will be complicated and expensive. Au contraire!
> How many of you have a 20 to 40 inch dish you use to watch TV?
> Well, the downlink that DirectTV uses is well up in the microwave
> spectrum in Ka band, at about 12 GHz. Many of the other TV
> satellites operate at ~11 GHz. Hams in several parts of the world
> have found that the feed used in these dishes (called an LNB)
> consists of a good feed (designed to work with the small offset
> dishes) coupled to a HEMT Low-Noise Amplifier (don't believe the
> advertising -- the Noise figure is closer to 1 Db and not the 0.1
> dB the vendors claim). The LNA feeds a crystal-controlled down
> converter which, off the shelf, makes the IF come out around 700
> Mhz. I can go on Amazon, Ebay or Alibaba today and purchase a dish
> plus a full LNB plus some dish mounting hardware plus 100 ft of
> low-loss (foam) 75 ohm coax and have it delivered to my house for
> less than $100.
> The ~700 MHz IF can plug into a $200-300 RX SDR which converts the
> ~10 MHz wide downlink into usable signal channels. Instead of
> tuning an analog frequency dial, you will select an appropriate
> channel to listen to your buddies. Or you can feed the SDR into
> your local VHF/UHF LAN where you can user your existing HT. If you
> are a skeptic about using the TVRO hardware in the amateur world,
> I'll note that just such hardware has successfully copied the DL
> 10GHz EME beacon in San Diego using a DVB Dongle+a laptop as the
> What I described was the downlink side. The ~6 GHz uplink will
> require the addition of a 1-5W PA, a small (probably array of
> patches) with the TX side of an SDR and an upconverter from
> whatever IF your SDR can generate to 6 GHz. The C-band TX should
> cost under $500-$600 with the bulk of the cost in the SDR and TX PA.
> If you add up the RX and TX hardware, the tariff is less than the
> price of an FT-1200 or KX-3, i.e. under $1000. We are working hard
> to meet this goal since it meets FEMA requirements for portable
> first responder "Go Boxes" to cover the need during major
> disasters (Katrina, tsunamis, earthquakes) for reliable
> communications in the first 24-96 hours. The ARRL and FEMA have an
> agreement to have a hundred such "Go Boxes" (which also includes
> suitable portable radios to augment whatever local resources exist).
> For those of you who want to use "conventional" modes our current
> plans call for a ~100 kHz wide LINEAR C/X-band transponder. I note
> (with pride) that I have figured out how we can have a LINEAR
> transponder built on RX software running the "main" payload and
> getting a LINEAR ANALOG output from a hard-limiting digital PA.
> Using the linear transponder will require you to have a bit
> antenna/TX power, but it will be there as a challenge!
> For all the nay-sayers please realize that AMSAT is trying to make
> a miracle happen. We need financial, moral and technical support.
> The "Space Biz" of today is radically different from what it was
> when NASA and ESA were launching their own rockets and when AMSAT
> was able to get sympathy for a bunch of "Space Cadets".
> 73 de Tom, K3IO (ex W3IWI)
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