[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

More Mars info and questions

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:

[ 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

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

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 [1] we can just use SCET as UTC or [2]
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
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

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