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Re: [linrad] More Mars info and questions
I asked almost the same questions on Mars-net and got the following info:
SCET is basically UTC on Mars, so the signal will appear cca 3 min (OWLT)
after end of occultation as given in SCET.
(Add OWLT to SCET to get UTC on earth)
BTW, if you don't have QRM (that is, if you can only hear (or see on FFT)
noise) then there's no need to sample at 16 or 24 bit precision (even 8bits
is too moch, but it's the lowest sound cards will go.) You only need more
bits if you need to filter out strong QRM - but then it probably hopeless
Doppler is +-4Khz max (even less during the time the signal is available)
so there is no need to record more than 10kHz of bandwidth either.
If you know the doppler and your RX frequency, SSB bandwidth will do.
Even if you keep your RX frequency fixed - during the time (<15min) when
the signal could be available, the change of doppler is less than 800Hz.
You'll only have to retune your rx between EOCCSE end EOCCSB and
Since in the final processing, bandwiths of one Hz or less will be needed
for detection, locking to a rubidium or GPS clock will be handy.
In absence of these, the receiver should at least be stable to <1Hz
during the few minutes of available integration time....
I have asked S51ZO to use his 70cm array (8X10WL DL6WU).. this
weekend I'll visit him to check the sensitivity using celestial sources.
If it's OK, I'll probably make some recordings for later processing.
There is of course no hope of real time detection.
73, Marko S57UUU
On Friday 22 August 2003 05:58, w3sz wrote:
> Hello, All!
> Here is some more information on the Mars Relay UHF tests, and a request
> for clarification by those of you who know spacecraft lingo as to what we
> need to do with the SCET times listed in the pdf files Joe directed us to:
> [ http://18.104.22.168/~km1p/ is the page of Joe's that has the helpful
> data files]
> This page contains Link Budget data you can adapt for your system as well
> as other data. The file MGS_Events.pdf gives the potential times for the
> CW tests, from 8-26 to
> SCET is 'spacecraft event time' and is basically if I understand correctly
> UTC onboard the spacecraft at the time the spacecraft perceives event in
> question. When a signal is sent from earth to a spacecraft, SCET = TRM +
> OWLT, where OWLT is one-way light time and TRM is UTC when the transmission
> is sent from earth to a spacecraft.
> I have not heard this term before, and thus I don't know if when the signal
> goes from the satellite to earth if we need to add the transit time to the
> SCET to get UTC, or if the SCET times listed in MGS_Events.pdf are just our
> UTC, having already been corrected for transit time. I am hoping someone
> with more knowledge than I can answer this. It would be nice if either 
> we can just use SCET as UTC or  someone else has done the correction.
> If I did my math right the OWLT is about 3.1 minutes for this case [see the
> file MGS_Geocentric_Doppler.pdf]. So it does make a bit of difference,
> especially if you are planning to record 16 or 24 bit 90 KHz wide Linrad
> data files and want to record them at the right time ;)
> I would assume that we would need to listen for signals sent from 15 to 0
> minutes before EOCCSB and for 0-15 minutes after EOCCSE as listed in the
> file MGS_Events.pdf.
> The question I can't answer is can we just use the SCET times listed in
> this file or do we need to add 3.1 minutes for the OWLT to the SCET times
> listed. [and of course I could have done the math wrong].
> Also, I think the Link Budgets were done when the spacecraft was 2.1 to
> 2.8E+10 meters
> distance, and now I think that it will be 5.58E10 meters away so the link
> budget would need to be adjusted for that as well as for receive antenna
> gain, etc.
> I am planning to use my 4 M2 4329WL array with GasFET preamp at the power
> divider going to an SSB electronics LT70S. I will then hook up 2 TUF-1H's
> with a 1/4 wave length of coax to give me the phase shifting to the Linrad
> Box, and Linrad will function as my 28 MHz IF rig which I will need to tune
> to 33 MHz. If the Helical filter in the preamp on the mast is too narrow,
> I am dead in the water. If the filters in the LT70S are too narrow I will
> do some playing with the LT70S, or alternatively try to pull off the IF
> from one of my IC970's, as they go up to 450 MHz. I won't get 90 KHz of
> bandwidth for Linrad then, but I should get at least 15 KHz.
> Comments appreciated! I am quite sure I have made some errors as I have
> not thought about any of the above subjects before writing this email. It
> is fun, though ;)
> Roger Rehr