On 1/1/19 4:05 PM, Mark Goldberg wrote:
On Tue, Jan 1, 2019 at 4:40 PM Jeff Blaine <keepwalking...@ac0c.com> wrote:
Take a look at the plots at the bottom of this page.
http://hpmemoryproject.org/technics/bench/3048/hp_sources_02.htm
Note the 8642b vs the 3325B. The '42b has much lower ultimate noise far
out but see how decent the 3325B is in comparison. HP really made great
stuff back in the day!!!
Thanks for pointing out that page. My measurements of my 8642A looked
better than that far out, but are pretty similar close in. Comparing the
3325B to my measurements of TCXOs and transmit Phase noise of the TS-590,
I'm not sure it will be good enough far out to meet the 590's original
performance.
The reason for good phase noise in amateur gear is if you operate in close
proximity to another strong station while trying to receive a weak one. The
phase noise will cause far out noise from the strong signal to overwhelm
the weak one. There are lots of examples on the web, explained better than
I could.
Has someone measured the reciprocal mixing noise contribution from the
TCXO - You've got measurements on the *output* of the transmitter using
the various reference oscillators, and, of course, there's measurements
on various bare oscillators and signal generators.
I suppose that's the sort of thing you'd get with a "strong signal next
to weak" receive test.
But the original question was "how good does it have to be"...
That is, what numerical performance is needed for an HF transceiver? For
CW or SSB? for one of the digital modes like WSJT or PSK31 ?
The propagation path itself has a fair amount of "phase noise" in the
single digit Hz sort of bandwidth due to ionospheric effect, but you're
looking a bit farther out as far as a undesired strong interfering
signal rejection standpoint.
Mark, your first set of plots show the output phase noise being the
same, regardless of TCXO, from 100-1000 Hz, which is where I think you'd
be concerned, even for CW. The CW signal itself is on the order of
100-200 Hz wide (depending on the keying waveform). So you'd not be as
concerned about the 10 Hz out phase noise..
And of course, if the strong interfering signal you're trying to reject
with good receiver performance has crummy Tx noise that's another problem.
We see this all the time when folks try to use mass market design
approaches for space flight. Your product may meet FCC requirements of
being down 40dB or 60dB out of band/channel, but still be intolerable if
you're radiating a carrier 1 mW (so your spurious emissions are at
-60dBm), and we're trying to receive a signal at -150dBm in that
adjacent band/channel. Example, 802.11, BT or 802.15 transmitter
spurious outputs in the 7.15 GHz deepspace receive band, especially
into the omni receive antenna used in safe mode.
This was the whole problem with LightSquared (or whatever their name is
now) - 10kW transmitters in a band adjacent to GPS L-band.
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