[time-nuts] Need 10 MHz for DSN space-probe hunting
mpb45 at clanbaker.org
Tue Sep 13 13:04:41 EDT 2016
Full disclosure-- I am a complete newbie at understanding the
intricacies of generating a really stable, low phase noise, accurate
frequency reference for microwave reception up around the 8 GHz
DSN (Deep Space Network) band. I have been following the back
and forth comments on the Time-Nuts list about improving the
Trimble T-bolt's 10 MHz output but confess that most of it is pretty
much deeper technical voo-doo than I am comfortable with.
I have been following the exploits of a group of folks around the
world who receive the incredibly weak signals from space probes
such as Juno. The idea is to detect the signals and then deduce
and confirm what probe is being detected by analyzing its doppler
and orbital characteristics.
This is being done at around 8.4 GHz with relatively small dishes of
under 8-ft diameter. Part of the magic that permits identifying
signals so far below the noise floor is the ability to use very narrow
bandwidth; as little as couple of Hz or even more narrow than that.
In order to do this a really accurate/stable/low phase-noise frequency
reference is needed.
I have been running a Trimble T-bolt 24/7/365 on Lady Heather
for around 5 years but have just started to take note of comments
on this list that the T-bolt is not really very good as a source to
phase-lock to for producing super narrow bandwidths of only one
or two Hz at 8 GHz. The comments I hear on the DSN space-probe
hunters chat-list is that obtaining a really high quality freq reference
is one of the big obstacles to success at this game.
My workbench test gear is limited to a pair of spectrum analyzers
(Tek 495AP and a Tek 494AP) and an HP 8714ES Vector Network Analyzer.
John Miles was the source for the Tek 495 spec-analyzer a few years ago.
John-- you might recall the check I sent you for the Tek495AP that
got lost...? Did it ever turn up?
Accordingly, what possible options might I have open to obtaining
a decent 10 MHz frequency reference for working up at the 8 GHz
DSN band? Any feedback on this will be much appreciated!
(Micanopy, actually, about 12 miles south of Gainesville)
As a side note, I built a tracking downlink to receive and display
the digital imagery from the environmental low-earth polar orbit
satellites several years ago. This HRPT data comes down at around
1.7 GHz. The USA, Russia, Japan and China each have 2 to 4 of these
low-earth orbit birds (100 minute orbits) and one of them passes
overhead every other hour or so. I have a lot of trees around my
house and these limit my open-sky area but I can still start to get
solid reception when the birds pass over Cuba and drop-off when
they are over Tennessee.
Photos of my home-brew tracking station can be seen here in the
back yard behind my workshop building:
And some low-res screen-grabs of false-color infrared earth surface
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