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Re: 10.0 - 10.5 GHz LNBs and upconverter-TX units.


Yes I am aware of the limitations of commercial DRO LNB's, LNC's from
another of my interests: Radio astronomy.  A few months back a similar
subject was discussed on the SARA list {converting their use for SETI}.
They were determined unsuitable due to poor phase noise.  I had suggested
that maybe locking to a phase stable PLL would improve performance but
Charles Osborne, Technical Director of Pisgah Radio Astronomy Observatory,
professionally worked in their design in his previous engineering career,
had very poor results in trying to improve their phase-noise.  He suggested
that such efforts were likely to result in frustration, and that I would be
better off looking elsewhere for suitable LO's.  An alternative would be to
build a good LO for use with one of these LNB's.  The choice is whether you
want to hack on one or just build one from scratch.  My choice was simply
to buy a well built one :-)   

I held of getting into this discussion to see what others would discover.
I have a Kuhne 10 GHz preamp and am very impressed with their construction
and performance.  You will not go wrong choosing his equipment though price
in the US is higher than DEM.


 >From: Achim Vollhardt <avollhar@physik.unizh.ch>
 >Hi Ed and all..
 >as I already posted earlier in another thread, commercial 10 gig lncs
 >are no good for narrow bandwidth ssb, because of bad phase noise. The
 >frequency drift and stability of a dro might be sufficient though
 >annoying because it surely will drift around a couple of 100 khz's..
 >But the problem of phase noise is as follows: imagine you have a cw
 >signal normally audible with your cw-filer with say 500 hz width.. now
 >imagine this cw-signal on 10 gig will be downconverted to your IF by a
 >signal with a width of a couple of 10 khz (10000 Hz !). As converting
 >means mixing, your mixed IF signal will be something with similar width
 >(10 khz).. now imagine listening to this with a 500 Hz Cw filter. I did,
 >and it was not very promising.  8(
 >Same assumptions are valid for SSB, though the effect is not so strong,
 >but nevertheless you have a loss in SNR.. which is very undesireable for
 >weak signal reception like sat-ops..
 >The most promising device seems to me the downconverter of Michael Kuhne
 >(www.db6nt.com). He already made transverters for terrestrial ssb with
 >conventional crystal multipliying, so I guess this is the way to go,
 >although I also would like the DRO thing.. 8(
 >73s Achim, DH2VA
 >"Edward R. Cole" wrote:
 >> If you have the time, skill, or willing to acept the risk then go for it.
 >> If not, then DEM, SSB, Kuhne, Parabolic, etal offer a good selection.

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