[time-nuts] Need 10 MHz for DSN space-probe hunting

Bob Camp kb8tq at n1k.org
Tue Sep 13 20:40:31 EDT 2016


A more significant issue with the output of the TBolt for direct microwave multiplication
is the spurs on the output. When multiplied up to > 1 GHz, these are going to be a major
issue. There are a lot of conventional techniques for taking care of this. If you have not 
already employed them, they are probably the first thing to take a look at. 

For cross correlating signals, the time sync of the signals is at least as important as the
frequency error. As with phase noise, there are a lot of ways to address this. Most of the
“better frequency” suggestions here are also “worse time” suggestions. 


> On Sep 13, 2016, at 1:04 PM, Mike Baker <mpb45 at clanbaker.org> wrote:
> Hello, Time-Nutters--
> 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!
> Mike Baker
> Gainesville FL
> (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:
> *http://tinyurl.com/j676ap2*
> And some low-res screen-grabs of false-color infrared earth surface
> images here:
> http://tinyurl.com/jsv323l
> *http://tinyurl.com/jvxkc9g
> **http://tinyurl.com/hbo886y*
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