My original back of the napkin calculations showed a 6-8' dish, so yes, this seems approximately correct. Point to keep in mind: the 10 dBm will not be the Tx power. 10 dBm will be the maximum Tx power. Due to bad orientation, we expect to only receive a fraction of that, unless someone gets particularly lucky with ISS orientation. I'll be simulating exactly how much of a fraction over the next few days, and of course could do so for anyone's particular location. Robert
On Wed, Jul 14, 2010 at 4:32 PM, Edward R Cole [email protected] wrote:
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.  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).  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.  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.  Each of these dipoles is mounted a few mm from large metal panels on the ISS.  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.  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.  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 [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
73, Ed - KL7UW, WD2XSH/45
BP40IQ 500 KHz - 10-GHz www.kl7uw.com EME: 144-QRT*, 432-100w, 1296-QRT*, 3400-fall 2010 DUBUS Magazine USA Rep [email protected] ====================================== *temp