Since I'm proposing X-band as a downlink, the main issue is LO phase noise requrements for C-band uplinks.
The downlink operates at 20 times the bit and baud rate of the uplinks, so I don't think that we will encounter LO phase noise problems there. The most critical LO will be that for the C receiver. However, PSK31 (31.25 Baud) is being used successfully at 30 MHz and the class 2 uplinks (4800 bps) will operate at 9600 Baud or more. This indicates that operation is possible at 30 MHz * 9600/31.25 or 9.216 GHz for class 2 users. Actually, operation is possible at much higher frequencies as the LOs in many HF radios are quite noisy and we can design low phase noise LOs.
Doppler shift is another issue, but 1200 Baud links are used routinely at 435 MHz in LEO satellites and a HEO will have 10 times less Doppler. This implies that operation is possible at 435MHz * 10 * 9600/1200 or 34.8 GHz.
Another way to look at the problem is that we are planning on 30-50 bps class 1 users on 435 MHz. If we can do that, then we can support 4800 bps class 2 users at 435 MHz * 4800/50 or 41.76 GHz. We were originally planning on having class 1 users using a C-band uplink and class 2 will be much easier.
I still like S1/C, but if there is decision that it isn't feasible for non-technical reasons and we can't be absolutely certain that L/C will remain available everywhere through 2030, C/X is better than LS2/C by providing better worldwide availablity of the satellite.
73,
John KD6OZH
----- Original Message ----- From: "Robert McGwier" [email protected] To: "'EAGLE'" [email protected] Sent: Thursday, September 14, 2006 09:19 UTC Subject: [eagle] Recent arguments and proposals, I am off to Tuscon
I spent yesterday in a lawyer's office in Washington D.C. for AMSAT and actually enjoyed myself. I followed that with a mad dash back to Trenton to teach the SDR class Frank and I are teaching. Microchip is assisting us beautifully and we have a class full of eager students wanting to take on Suitsat-II and Eagle pieces for their design projects. I apologize for this week being so busy for me that I am unable to jump on to much of the discussions this week on BB and here in Eagle.
Let me dash off some quick comments.
I do not believe we can successfully build the X band component to the modified DCP system. I believe we will be killed by all sorts of LO problems including, but not limited, to phase noise issues. I am already a week behind in delivering Stephensen an analysis of the phase noise on the Class 1 users in SDX, I will add to this a system analysis of the required oscillator performance to use X band in the DCP. Remember, this is a weak signal mode and we are attempting to operate with only a few dB of margin at best. We cannot shed 1 or 2 more in implementation loss (if we are lucky).
I support John's contention that we should choose a band that is currently available world wide for the uplink on which we can feasibly build a system. Pick L or S1 is my recommendation. We chose S1 for all of these reasons.
If you choose L, we can put in two L's or share one with SDX. The antenna is the same required area, but the packing of the antenna on the spacecraft becomes more problematic. I understand Rick's motivation to not get hammered at the annual meeting. Welcome to the presidency. It is not a reason to make a bad choice for the uplink which will kill the utility of the package is my current opinion.
My current vote: stay with what was decided in San Diego or risk L as the primary uplink. I believe that a serious analysis of the impact of trying to get the dual band L/C antenna packed together will be a very illuminating exercise and I believe we will inevitably be led back to the SD decision based on system analysis rather than emotional analysis.
Bob
-- AMSAT VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats, NJQRP/AMQRP, QRP ARCI, QCWA, FRC. ARRL SDR Wrk Grp Chairman "You see, wire telegraph is a kind of a very, very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? And radio operates exactly the same way: you send signals here, they receive them there. The only difference is that there is no cat." - Einstein
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