dflynch@vax1.tcd.ie (08/28/89)
In article <17463@bellcore.bellcore.com>, karn@ka9q.bellcore.com (Phil Karn) writes: > Here's another link calculation for Voyager 2 at Neptune. I got some more > precise figures, and the result looks pretty reasonable. My references to > "Yuen" are to the book "Deep Space Telecommunications Systems Engineering", > edited by Joseph H. Yuen and published by Plenum (ISBN 0-306-41489-9). > > 8415 MHz transmitter power +11.04 dBW > (12.7 W - low power mode ref Yuen): > 3.7 m spacecraft antenna gain > (ref Yuen p 4): +48.13 dB > EIRP: +59.17 dBW > > Path loss, 4.416e9 km, 8415 MHz: 303.85 dB > = 20 log10(4*pi*d*f/c) > > Receive signal flux: -244.68 dBW > > 70m receive antenna gain: +73.8 dB > = 10 log(4*pi*A/lambda^2) - N > lambda = C/8415e6 = 3.56cm > (assuming N = 2 dB illum loss) > > Receive signal power: -170.88 dBW = 8.16e-18 W > = 8.16 attowatts > = 8.16 nano nano watts > > Received energy per bit (Eb): -214.22 dBJ = 3.78e-22 J > at 21.6 kb/s (43.34 dB-b/s) = .000378 attojoules > = 0.378 piconanojoules > > Receive noise density (N0): -218.60 dBW-Hz > = 10 log10(kT) > T = 10 Kelvin (ref USENET) > > Eb/N0 ratio: 4.38 dB > > This is quite consistent with the performance of the concatenated rate 1/2 > Reed Solomon + rate 1/2 convolutional coder, which according to Yuen (p 255) > has a very steep "wall" or threshold just below 3 dB. > > However, this figure does not take into account miscellaneous losses > (connectors, feedlines, etc) on board Voyager or at the receiving site, nor > does it allow for atmospheric absorption or transmitter degradation below > the nominal 12.7 watt figure. > > According to an interview carried tonight on NASA select, the arraying of > the VLA to Goldstone effectively doubles the aperture of the receiver, so > this should give another 3 dB of margin to compensate for these factors. > > As you can see, attention to detail is all-important here! > > Phil JPL AMATEUR RADIO NETWORK LINKED TO VOYAGER PROJECT ACTIVE UNTIL SEPTEMBER 9. TIMES UNCERTAIN, BUT 21335 AND 14235 KHZ USB USED. ALSO 3.8* MHZ OUTLET. I HAVE HEARD NO NASA TRAFFIC ON 20192 / 20198, FREQUENT NASA CHANNELS HEARD HERE. ANY MORE DETAILS BEFORE IT IS TOO LATE ? POST TO NEWSGROUP