[amsat-bb] Re: Since there's been a lot of ISS chatter recently, I thought this might be a good time to post

[Edward R Cole]

Here is what I calculate:
10 dBm  Tx power
0 dBic    zero gain Tx antenna
20 dBic   Rx antenna gain
0 dB       Cross polarity loss
902 MHz
0.001 millions of km (1000km)
20 K       sky temp
40 K       Rx antenna temp
36 K       receiver noise temp
200000 Hz   bandwidth

151.5 dB     space loss at 1000km
-121.5 dBm  received signal level
96 K           total receive system noise temp
-125.8 dBm   EIRP
4.3 dB         S/N

this was calculated using the spreadsheet I made 
for determining the signal from MRO:
http://www.kl7uw.com/raseti.htm
click on the word "calculate" to download the spreadsheet.
this works for determining any spacecraft signal reception.

A 20-db antenna will have around a 10 degree 
beamwidth so much easier to point than what hams used for AO-40 on 2.4 GHz

probably a 4 to 6 foot dish will suffice.



At 08:40 AM 7/14/2010, Robert Christ wrote:
>Hey everyone.  I'm a researcher at Cornell, and 
>this fall, our experimental, 1 inch diameter, 
>“chip satellites” are scheduled to be 
>launched on the final space shuttle flight, 
>STS-134.  They're going to be mounted on the 
>exterior of the ISS structure, and will be set 
>to transmit a 902 MHz signal.  Unfortunately, 
>we do not yet have an antenna for receiving this 
>transmission. Â After talking with Bob - Wb4APR 
>for a while, it was suggested that the fine 
>members of the AMSAT ­ BB might be able to helpp 
>us. What we’re looking for is a digital 
>capture of this 902MHz frequency (with a 
>bandwidth of about 200KHz), during at least one 
>ISS pass (only a few gigs of data, we believe). 
>Â No decommutation or other analysis of the 
>signal will be required, but actually capturing 
>the signal will require at least a 20 dbB gain 
>receive antenna (more details in a minute). If 
>any of you can help us in this experiment, or 
>are able to successfully capture the signal, not 
>only would we be incredibly grateful, but we 
>would also be prepared to add your names and 
>contributions to all of the published papers 
>that will result from this mission. Â It goes 
>without saying, though, that we’d also be 
>entirely open to suggestions if the community, 
>or a member, were aware of some manner by which 
>Cornell might be able to better avail itself to 
>the both those who help us on this project and 
>the community as a whole. So here are the 
>technical details.  There are 3 transmitting 
>antennas, all tiny, center-fed dipoles: two of 
>them use wires separated by 180 degrees, and one 
>has wires separated by 90 degrees. Â Each of 
>these dipoles is mounted a few mm from large 
>metal panels on the ISS. Â The ChipSats will 
>transmit for approximately 10ms every 1-2 
>seconds, but the signal is going to be beneath 
>the noise floor.  Detecting the signal requires 
>a pseudorandom noise (PRN) code, which Cornell 
>will handle once the dataset is in hand. Â Since 
>we can/will take care of the post processing, 
>and capture isn’t guaranteed on every ISS pass 
>(attitude alignment problems still TBD) so 
>anyone who can take a recording of this 
>frequency at this bandwidth for us, of any ISS 
>pass, would be incredibly helpful. The good news 
>is that the chips will be live and transmitting 
>almost immediately after they are installed from 
>STS-134, and they will transmit continuously 
>whenever the ISS is in sunlight. Â Additionally, 
>should they survive in their environment, they 
>are set to transmit for up to two years, which 
>should give us many chances to receive the data 
>and confirm that the ChipSats are functioning. 
>Thanks for your time, everyone, Robert Christ 
>http://www.spacecraftresearch.com/ P.S. a little 
>extra information:  Our website is 
>http://www.spacecraftresearch.com/projects.html 
>if you're interested. This mission isn't 
>explicitly mentioned there yet, but is rather a 
>proof of feasibility study for most of the 
>projects listed on that site.  Ah and lastly, 
>the ERP of the transmitter is expected to be ~10 
>dBm, though it will almost certainly be facing 
>in a poor orientation, giving us only a fraction 
>of that power.  We won't know the exact amount 
>for a few more days.  Thanks all! 
>_______________________________________________ 
>Sent via AMSAT-BB at amsat.org. Opinions expressed 
>are those of the author. Not an AMSAT-NA member? 
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73, Ed - KL7UW, WD2XSH/45
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