Jim,
To help with your question, some good phase noise numbers to ponder are as follows:
Using direct synthesis techniques (multiply/mix/divide and not using any PLLs or VCO's - this would be like the Comstron and PTS series of synthesizers), which use a low noise 10 MHz reference and will provide phase noise performance as follows:
600 MHz - -138 dBc/Hz at 10 KHz offset 1.2 GHz - 132 dBc/Hz at 10 KHz and following the 6 dB increase each time the frequency is doubled, -114 dBc/Hz at 10 KHz at 9.2 GHz.
A very low noise VHF crystal controlled oscillator/multiplier designed for a X-Band military doppler RADAR will do -118 to -124 dBc/Hz at 10 KHz.
I have seen -132 dBC/Hz at 10 KHz at X-Band in the laboratory using a fundamental mode cylindrical cavity oscillator (about the size of a coffee can). That's close to the ultimate low noise X-Band source - the double cavity klystron. Some chaps in Australia are doing about that with something called a smaller whisper mode cavity - if memory serves me right.
A really good free running transistor, not FET, DRO at X-Band will do about 85 to 90 dBc/Hz at 10 KHz. The FET DRO will be 10 to 15 dB worse.
The point I'm trying to make is that these numbers are obtained with considerable pain (complexity and size). So to get -110 dBC/Hz at 10 KHz at C Band for instance, you'll have to resort to a sophisticated low noise VHF crystal oscillator locked to a low noise 10 MHz oscillator and then multiplied to C band using pretty tight filtering along the way to reduced the spurious to less than -60 dB. Not exactly your straight forward PLL IC chip and a good dielectric resonator VCO.
Now if you ask what phase noise and at what distance from the carrier is required for a particular modulation format, then those numbers can become a little more argumentative since many variable factors enter into the equation. It can also matter if the signal is used as a receiver LO or a transmitter LO.
Now finally - - - for my opinion about your question for what do you need for X band terrestrial narrow band work, it appears to me that most X-Band EME is done with LO's running around -90 to -110 dBc/Hz at 10 KHz which is what the typical CMI or Frequency West phase locked cavity oscillator/multipliers will do but I'm convinced even -70 dBc to -80 dBc/Hz at 10 KHz. (or even worse) will also work. More important, for CW and SSB, what is the phase noise at 0.5 to 4 KHz.
As a point of note, the phase noise functional specifications for the JPL Mars Reconnaissance Orbiter SDST (Small Deep Space Transponder) receiver and exciter are ≤ −20 dBc/Hz at 1 Hz, ≤ −60 dBc/Hz at 100–1000 Hz, and ≤ −70 dBc/Hz at 1–100 kHz.
Well hopefully - - - the satellite system guys have our required numbers figured out and will be sharing them with us sub-system component guys real soon!!!
Jim Sanford wrote:
Bill: -110 dbc/hz at 10khz offset is what I REMEMBER in my response to the question, "What is a good phase noise number to shoot for in a microwave narrowband (ssb/cw) system?" My memory may very well be WRONG, which was the point of asking my question.
I agree with you, looks like -90dbC at 10 KHz, but given what Juan's already said about his sources, and the uncertainties of the SDR-IQ, that may be VERY good!
Do you have a different answer to my original question, "What is a good phase noise number to shoot for in a microwave narrowband (ssb/cw) system?" If so, I'd like to engage in that conversation, both for Eagle and for my terrestrial microwave station.
I agree with your assessment of Juan's work -- ABSOLUTELY EXEMPLARY!!!!!!
Thanks & 73, Jim [email protected]
Bill Ress wrote:
Jim,
Where did the -110 dBC/Hz at 10 KHz come from? And at what frequency? That's pretty aggressive using straight forward VCO's and PLLs. From Juan's data with his snappy SDRIQ, it looks like that the 70 cm is doing about -90 dBc/Hz at10 KHz. I thought that's what I read from his early HP8566B dtata.
My straight forward S2 RX downconverter PLL LO does -100 dBc/Hz at 10 KHz.
We'd better get a good read on this since, if real, it forces more sophisticated LO designs.
Great work Juan!!
Regards...Bill - N6GHz
Jim Sanford wrote:
I think I remember Bob's answer as -110dbc at 10 KHz offset.
Thanks & 73, Jim [email protected]