[time-nuts] HP3325B as LO for a transceiver or receiver? Phase noise?

[jimlux]

On 1/1/19 4:05 PM, Mark Goldberg wrote:
> On Tue, Jan 1, 2019 at 4:40 PM Jeff Blaine <KeepWalking188 at 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.