[eagle] Some Phase Noise Numbers!!

Bill Ress bill at hsmicrowave.com
Sun Jun 10 23:10:47 PDT 2007


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
> wb4gcs at amsat.org
> 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
>>> wb4gcs at amsat.org

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