Tom, I was at the 2015 symposium but what you have posted adds more detail as to the progress of the design. I think periodic posting on this BB would be nice for those of us that are interested in how things are developing. I have also been puzzled by the hams that won't support AMSAT because we are not doing HEO and when we do what they ask for complain about the technology required. I wonder if all of the hams that cancelled their memberships because AMSAT was not doing HEO have now renewed their memberships. AMSAT is trying to pull off a miracle in about a year. If succesfull, this will again put amateur radio sattelite operation at the bleeding edge of amateur built technology. Thank you for the update. Looking forward to more. (I understand their are restrictions with regard to the satellites but I belive their are no restrictions with regard to the ground stations).
From: Tom Clark [email protected] To: [email protected] Sent: Monday, December 28, 2015 4:00 AM Subject: Re: [amsat-bb] What on earth (or in space...) is going on?
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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