FYI I have attached a copy of that study. I would point out that people often do not respond positively to new concepts they do not truly understand the application of, or long term possibilities of. With other words, many of the responses are based solely on PAST experience and might lack VISION. Regards, Gunther
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Robert McGwier Sent: Monday, September 18, 2006 9:35 AM To: John B. Stephensen Cc: 'EAGLE' Subject: [eagle] Re: C-C Rider Band Plan Follow-up
Guenther Meisse conducted a survey for AMSAT on member preferences. That data would be more useful than anyone's anecdotes based on a few received emails, phone calls, and amsat-bb dreck.
I would like for us to concentrate on the engineering and then factor in the political choices between L,S1,S2,C. A decision is coming and soon.
Bob
John B. Stephensen wrote:
If the X-band PAs occupy a 30 x 30 cm area, isn't the dissipation 42/900 or 47 mW/cm^2? This would result in 1/10 the temperature rise.
73,
John KD6OZH
----- Original Message ----- From: "Dick Jansson-rr" [email protected] To: "'John B. Stephensen'" [email protected]; "'Robert McGwier'" [email protected]; "'EAGLE'" [email protected] Sent: Sunday, September 17, 2006 18:35 UTC Subject: RE: [eagle] Re: C-C Rider Band Plan Follow-up
The consideration that John has made for an X band downlink is fraught by practical issues. The specific one that I address is that of the transmitter power dissipation. He proposes a 60W DC input to 36 amplifiers with an 18W RF output. Leaving 42W to be dissipated in a rather small area, which looked like an area of no more than 0.10m^2 (~>300mm each side of a square).
To grasp the magnitude of such a thermal issue that John's plan presents, let us examine the results of his plan. The proposed dissipation amounts to a heat flux of 0.42W/cm^2. If all of this had to be radiated to space on only one side, a ridiculous solution, the temperatures would achieve levels in the range of: Ta = 534K or 261°C. Presume then that only half of the 42W is directly radiated to space, the other half removed to the spaceframe, the temperature of the array would then come down to only: Ta = 449K or 176°C.
It is clear that such a plan as John proposes cannot be achieved without a pretty involved heat pipe cooling system, not just in a line but over an area. To me such a system is a bit mind boggling. I am not rejecting heat pipes, I worked them for AO-40, but such a system is very rapidly running away from one of the primary tenets of Eagle, that of
KISS.
It is easy for you to toss around antenna gains, noise factors, path losses, and the like, but sometimes consideration of these factors seem to loose sight of a practical satellite system where it actually has to be constructed in real hardware and suffer the ramifications of real hardware.
Dick Jansson
[email protected]
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of John B. Stephensen Sent: Sunday, 17 September, 2006 1629 To: Robert McGwier; 'EAGLE' Subject: [eagle] Re: C-C Rider Band Plan Follow-up
I agree that a 2-foot dish is useless at 1.26 GHz as it's slightly more than 2-wavelengths in diameter. S-band barely works at 4.5-wavelengths.
A C/X transponder seems feasible as there are efficient 500 mW X-band amplifier MMICs available. See the attached document.
73,
John KD6OZH
-- 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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