[amsat-bb] What on earth (or in space...) is going on?
n0jy at amsat.org
Mon Dec 28 17:12:00 UTC 2015
The use of, and reasoning for, the 5 and 10 GHz bands has been discussed
in the AMSAT Journal in my column this year. For those new members who
were not members before the Jul/Aug issue came out, I would be glad to
share a copy of the article. For those who are not members yet, please
consider that it is a benefit of membership to learn and understand what
AMSAT-NA is doing before the general public does - and even exclusively,
in many cases. There is much going on as you are beginning to see, and
you can help with it by becoming a member!
With that said, the short story here is that a very heavy factor for the
5 and 10 GHz is the volume limitation we have with a CubeSat, even a 6U.
You can't put an antenna for VHF or UHF that has enough gain for HEO/GTO
apogee on something about the size of two reams of paper stacked up and
have room for the solar panels that need the space outside the cube more
than anything else, much less fit it in a CubeSat deployer for launch.
Therefore, with the expectation that we will build and fly HEO CubeSats
in the near future it makes sense to use the same frequencies that we
will with those CubeSats on other platforms such as the P4B and possibly
P3E, so that the ground terminal we develop is something that works with
many opportunities and is not limited to just one satellite or series of
Between the volume requirements and the availability of hardware on the
ground as well as for space (as Tom pointed out), and the bandwidth
available on the 5 and 10 GHz bands, that is what drove the decision to
use those bands.
Jerry Buxton, NØJY
On 12/28/2015 04:00, Tom Clark wrote:
> 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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