January 2007 - AMSAT-BB - mailman.amsat.org

Linear link budgets
by Grant Hodgson 14 Jan '07

14 Jan '07

Unfortunately, the calculations for dividing transponder power equally amongst users are not as simple as have been suggested. For the 400mW case :- assume that 400mW is the maximum power that the transmitter can produce. Then a single CW signal could in theory be sent at a power of 400mW, assuming no AGC, beacons etc. However, if 2 equal level CW signals were being transmitted, then the Peak Envelope Power of these 2 signals would be 6dB higher than each of the signals individually. This is because the voltages of each of the 2 CW signals have to be added together, giving a peak signal with double the voltage of each signal, which is 4 times the power or a 6dB increase. Therefore, to keep within the 400mW limit, each CW signal would be restricted to 100mW each. The same analysis can be done for 3 equal CW signals, where each would be 9.5dB down; i.e. 44mW each etc. For SSB signals, the same analysis can be performed by simply taking the PEP of each SSB signal; so one CW signal could co-exist with one SSB signal, both of which would have a downlink power of 100mW. The above is actually a slight over-simplification, as it takes no account for compression etc, but serves as a useful example. As Graham mentions, a beacon may be present at a much higher level than the rest of the transponder, which makes the analysis slightly more complex, but the principle remains :- It's the PEAK power that limits the RF performance of linear transmitters, and that is valid for all linear transmitters. regards Grant G8UBN

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Re: Langrangian points
by G0MRF＠aol.com 14 Jan '07

14 Jan '07

In a message dated 1/12/2007 7:22:19 AM GMT Standard Time, w7lrd(a)comcast.net writes: Hello Amsat'ers Is it possible or practical to have a communications satellite at the L1 or L2 points. 73 Bob W7LRD Seattle Hello Bob. I finally got around to looking at The Langrangian points referred to in your mail. - Thanks for that pointer, it's a really interesting piece of physics. Good fun looking it all up. At a first 'pass' it would appear that maintaining a satellite at the L1 and L2 points would require some station keeping, hence fuel. They would give excellent coverage from 56,000km / 200,000km respectively. Tracking the one held between the sun and earth would give really simple tracking. Start by pointing at the sun and then move around a little to peak the signals. - Of course the disadvantage is that instead of cold sky you would have all the Sun noise. The L2 point is only visible at night...so may be a bit 'antisocial' for practical use. - I wonder how the eclipse works out there? The ones I found most interesting were the L4 and L5 points. Areas of space where satellites are held in a stable position by gravitational forces alone without needing any fuel. Big problem there is the distance. At 60 degrees ahead and behind the earths orbital position would make the path loss huge. Also, apparently, those areas tend to gather space dust, rocks etc. Probably a bit of a risk for collision albeit at low relative velocity. Very thought provoking 73 David G0MRF >From Wikipedia: The Lagrangian points also Lagrange point, L-point, or _libration_ (http://en.wikipedia.org/wiki/Libration) point), are the five positions in _interplanetary space_ (http://en.wikipedia.org/wiki/Interplanetary_space) where a small object affected only by _gravity_ (http://en.wikipedia.org/wiki/Gravity) can theoretically be stationary relative to two larger objects (such as a _satellite_ (http://en.wikipedia.org/wiki/Satellite) with respect to the _Earth_ (http://en.wikipedia.org/wiki/Earth) and _Moon_ (http://en.wikipedia.org/wiki/Moon) ). The Lagrange Points mark positions where the combined gravitational pull of the two large masses provides precisely the _centripetal_ (http://en.wikipedia.org/wiki/Centripetal) force required to rotate with them

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ideas
by Nick Pugh 14 Jan '07

14 Jan '07

Hi Amsaters The cubesat team at the University of Louisiana is in the process of defining its second mission for its cubsat project. The team has decided to fly a cubesat that has a educational component. We are asking for ideas that would excite K through 12 students that can be flown on a cube sat i.e. 1 watt of dc power in a 4 inch cube. In addition to the education component the team is thinking of flying a high efficient radio per haps bpsk with a forward error corrected code with Eb/No of < 3 db. Again here we are asking for input in the mission definition and help in the implementation including pier review. Please put your vision in gear and help us. thanks nick K5qxj

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FCAL Oscar Number
by Mineo Wakita 13 Jan '07

13 Jan '07

FCAL = NRL-OSCAR-62 or NO-62 http://www.amsat.org/amsat-new/news/ --------------------------------------------- Name: Mineo Wakita / JE9PEL, JAMSAT member Mail: ei7m-wkt(a)asahi-net.or.jp URL : http://www.ne.jp/asahi/hamradio/je9pel/ QTH : Yokohama Japan, GL:pm95tj Date: Jan 14, 2007 ---------------------------------------------

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PCSAT-1 COMAND-1 ?
by Andythomas 13 Jan '07

13 Jan '07

Following interesting frames received on 145.825 during PCSAT-1 pass this afternoon: Fm COMAND-1 To PA3GUO-3 <UA F >[16:48:00] Fm COMAND-1 To PA3GUO-3 <I R0 S0 pid=F0 Len=54 >[16:48:00] 57 37 67 2 9 45 63 80 48 72 4 10 45 31 16 48 24 12 Fm COMAND-1 To PA3GUO-3 <RR P/F R1 >[16:48:02] Fm COMAND-1 To PA3GUO-3 <I R1 S1 pid=F0 Len=7 >[16:48:02] prompt: Is this onboard PCSAT1? BTW argentinian satellite not heard on 80 degree plus pass - system can hear RAFT and ANDE-1. 73 de Andy, G0SFJ

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TNC for Motorola 56KEVM?
by Anthony Monteiro 13 Jan '07

13 Jan '07

Dear Friends, Does anyone know if there is software for a Motorola DSP 56KEVM that will emulate a complete AFSK TNC? I could find software for a 1200 bps, AFSK modem but it is KISS mode only, I would like to use the 56K as a drop-in TNC replacement. Thanks! Tony AA2TX

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PEHUNESAT-1
by Mr Jeffrey Ross 13 Jan '07

13 Jan '07

HI ALL, DID PEHUENSAT JUST COME OVER THE USA? WISP SAYS IT DID, SATSCAPE SAYS IT ON THE OTHER SIDE OF THE WORLD. PLS HELP IF YOU CAN, THANK YOU, KC8GKF

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PEHUNESAT-1
by Hakan Harrysson 13 Jan '07

13 Jan '07

Hello! Sorry to report nothing heard on a absolutley perfect overhead pass this morning. The band was completley silent and no other satellites in range. I was tuning +/- 10 but no lift in noise anywhere. 73 Hakan SM7WSJ

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simples and pcsat
by Nick Pugh 13 Jan '07

13 Jan '07

I am running pcsat and a Yaesu 736. How do you control the radio when running simplex? nick

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Re: Dnepr Launch 2
by Mineo Wakita 13 Jan '07

13 Jan '07

The launch has been delayed until March 2007 ? --------------------------------------------- Name: Mineo Wakita / JE9PEL, JAMSAT member Mail: ei7m-wkt(a)asahi-net.or.jp URL : http://www.ne.jp/asahi/hamradio/je9pel/ QTH : Yokohama Japan, GL:pm95tj Date: Jan 13, 2007 ---------------------------------------------

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