[amsat-bb] What on earth (or in space...) is going on?

Tom Clark 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
>     receiver.
>     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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