[EE] Phase locking DRO's
Robert Rolf email (remove spam text)
Given the diverse group on this list, perhaps someone can point
me in the right direction to solve this small problem: How to
Phase lock the cheap DROs (dielectric resonant oscillator) used in
consumer LNBs (C and Ku band) so that one can do interferometry?
Commercial PLL LNB's are way out of our price ranges ($1500 vs $50
for non-PLL) and the cheap versions have MUCH better noise figures.
I'm hoping that there is some simple way to control the on board
DRO so that a stable (and phase matched) LO can be achieved.
I've considered piezo electric (too slow). Varactors in proximity
to the cavity (doesn't seem to work but then I don't really know what
I'm doing). And plain old, change the VCC (again not fast enough).
Any suggestions on how one does a phase comparison at Ghz frequencies
(5150MHz) to a 100Mhz reference and then control a DRO would be
appreciated. I've been exploring a PIN diode sampler, but don't
seem to have the right configuration.
I have access to some decent tools, but they just don't
teach this kind of plumbing around here.
The other gotcha is how to ship a 1Ghz or so signal 300 meters (or 3 km)
without incurring huge losses (or outrageous cabling costs).
I assume that the same hardware that the cable people use for their
HFC plants would work. Know anyone with a couple of spare fiber
they'd like to donate to the cause <G>?
With the large number of big dishes (BUDs) being dumped in
favor of the smaller DTH (LSDs), we thought it was a real waste to see
them hitting the dumpster, so we have been taking the great unwanted up
to the roof of our physics building to bootstrap an amateur radio
astronomy observatory. The physical construction is going well, but
it now falls upon me to come with with a decent RF section so that
we can doing meaningful science. This means using interferometry to get
sufficient sensitivity and resolution. (Widely separated dishes can
behave like a single big dish with suitable signal processing. You just
don't get the sensitivity (or the pointing headaches) of a single
large dish). Computers are cheap. Sound cards are cheap (and so are
3D video cards. Subvert the DSP and you've got one heck of a
It is trivially easy to build a total power receiver (TPR) from surplus
C band hardware. Any of you who've experienced a sun-out (twice a year
sun passes behind the geosynchronous satellite and drowns out their
signals) have already done radio astronomy. It is much more difficult
to do interferometry since you need to either mix the signals from
two widely separated dishes at frequency (and the old LNA's had terrible
noise figures compared to today's LNBs), or have phase matched down
conversion and then mix the signal to get a correlation (and thereby
pull your extraterrestrial signal out of the noise). PLL LNB's are
just too expensive for an amateur group to afford, so I'm hoping to
be able to hack some cheap LNBs to do the job and get us started.
Thank you in advance for your time and suggestions.
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