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

[Robert Christ]

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 <kl7uw at acsalaska.net> 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. 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
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>
>
> 73, Ed - KL7UW, WD2XSH/45
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