[amsat-bb] What... in space... is going on? (Microwave Fun)

Robert Bruninga bruninga at usna.edu
Mon Dec 28 16:01:34 UTC 2015

And dont forget how you can take most old 10' dishs and disassemble it into
4 sections and make FOUR vrey high gain antennas.  Just mount the feed to
fully illuminate your  quarter section of the dish and you have adequate
gain in 1/4th teh space.  Lots of fun with microwafves..

I thought I had photos, but cannot find them.  I did find this old portable
briefcase 1m dish system I put together for AO40:


Bob, Wb4APR

On Mon, Dec 28, 2015 at 5:00 AM, Tom Clark <k3io at verizon.net> wrote:

> A related thread has been running on QRZ.com where I just posted this
> comment:
>     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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