[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 kl7uw at acsalaska.net
Wed Jul 14 13:50:40 PDT 2010

Sorry a labled two lines backward:
-121.5 dBm is Ps  signal level received from the s/c
-125.8 dBm is Pn  sensitivity of receive system
S/N = Ps-Pn in dB

I also ignored any squint angle for the 
transmitter on the ISS so that could add a lot more dB of loss.
But the link is not as bad as one would think reading the specs.

At 12:32 PM 7/14/2010, you 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:
>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?
> >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 dubususa at hotmail.com
>Sent via AMSAT-BB at amsat.org. 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 dubususa at hotmail.com

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