Phil Karn wrote:

I was going to model phase noise as 1/f^2, but Bob pointed out that the integral of that expression bounded at zero (DC) is undefined. So we need another, more realistic model of oscillator phase noise if we're going to compute its effect on digital demodulation.

Hmm. Is there more to it than simply doubling the spectral density?

Suppose you constrain the noise to be zero-mean. The spectral density will be 0 at f = 0. Then the noise has spectral density W(f) which is a real, even function of the bandwidth, so W(f) = W(-f). By convention only the spectral density at f >= 0 is considered, so you need to double the spectral density at f to account for the contribution at -f.

The zero-mean constraint is unrealistic, maybe.

Frank

Matt Ettus wrote:

Typically you only take a model like this down to about 1Hz. Below 1 Hz it can be considered flat or even zero. We don't much care about the phase noise below 1 Hz since the symbol rates are so much higher than this.

...which amounts to saying that it *is* as good as zero-mean, then, or at least that any DC drift is so slow as not to matter compared to the symbol rates.

Frank

Low frquencies will be dominated by the multiplied reference oscillator noise and high frequencies by the VCO free-running noise with an area of relatively flat phase noise in between. The simulation I've done may not be as accurate as possible as phase detector noise isn't specified for the SoI PLL ICs being used. However it may be easier to determine whether the existing design is adequate for the text-mode uplinks rather than come up with a general model.

73

John KD6OZH

----- Original Message ----- From: "Grant Hodgson" grant@ghengineering.co.uk To: "Phil Karn" karn@ka9q.net Cc: "EAGLE" eagle@amsat.org Sent: Wednesday, January 10, 2007 10:51 UTC Subject: [eagle] LO Phase noise (was : TeamSpeak conference for Tuesday 16Jan)

Phil Karn wrote:

--snip---

...

I was going to model phase noise as 1/f^2, but Bob pointed out that the integral of that expression bounded at zero (DC) is undefined. So we need another, more realistic model of oscillator phase noise if we're going to compute its effect on digital demodulation.

--Phil

This is a paradox which AFAIK has not yet been resolved properly. Assuming a low frequency cut-off of 1Hz as has been suggested is not ideal, but given that most oscillator manufacturers don't specify phase noise below this offset it is a reasonable compromise in practice.

However the 1/f^2 model is only valid above the flicker corner frequency, below which the noise rises at 1/f^3 to an undefined point where it rises at 1/f^4 due to 'random walk'. At very high frequency offsets the 1/f^2 term disappears and the noise becomes white, or gaussian, the level remaining constant with offset frequency. The flicker corner frequency could be as high as 100Hz or more, and so cannot be ignored. And this simple model applies only to free-running oscillators...

The 70cms Rx LO uses two Phase-locked loops. The noise behavior of a PLL is somewhat more complex than a simple free running oscillator. At frequency offsets greater than the loop bandwidth, the noise of the oscillator (i.e. VCO) dominates, making the analysis relatively simple. At offset frequencies close to and less than the loop bandwidth, many factors affect the noise behavior, all of which need to be considered. Fortunately analysis tools are available free from a number of sources which do a pretty good job of simulating the PLL phase noise for most practical offset frequencies. I don't know if a detailed PLL phase noise analysis has been done, I couldn't find one in EP.

As the two Rx LOs are independent, the total noise contribution will be non-coherent and can simply be added together. This is actually a simplification, as I believe that the reference for both PLLs is common, but this simplification should be OK.

Also, for digital systems one of the key parameters is the RMS phase error. Depending on what type of modulation is used (as well as the Rx S/N ratio), this parameter can have a significant effect on the system BER. The RMS phase error is an integral of the phase noise between two defined offsets and is easy to calculate, once the frequency distribution of the phase noise has been calculated.

regards

Grant G8UBN _______________________________________________ Via the Eagle mailing list courtesy of AMSAT-NA Eagle@amsat.org http://amsat.org/mailman/listinfo/eagle

Team: My apologies to each of you over not notifying you of this myself.

I asked Bob to get this sent ASAP because I expected that he or Rick would get to an unclassified connection long before I did. (Thanks Rick!!)

The rest of this week is out for me, I'll be in DC, returning to PA as early on Saturday as I can get my corpse vertical.

I am willing to meet on Sunday night, but none of MY agenda was that urgent. I think the channel is full and people otherwise opccupied next Tuesday, so how about Wednesday, 2100 EST, 1800 PST? This is a suggestion, I am absolutely open to better ideas, and additions to the agenda.

Thanks & 73, Jim wb4gcs@amsat.org

Rick Hambly (W2GPS) wrote:

All,

I was asked to inform the Eagle team that the meeting scheduled for tonight, Tuesday 16 Jan, has been cancelled due to a conflict with a last minute AMSAT Board meeting that will overlap the time for this meeting. Jim will reschedule this meeting soon.

Rick W2GPS AMSAT President

-----Original Message----- From: eagle-bounces@amsat.org [mailto:eagle-bounces@amsat.org] On Behalf Of Jim Sanford Sent: Monday, January 08, 2007 10:26 PM To: EAGLE Subject: [eagle] TeamSpeak conference for Tuesday 16 Jan

Team: I'm sending this out by email because I'm having some difficulties with the TS page on EaglePedia.

Things I'd like to discuss: 70cm RX status How many prototypes to build Goals for 2007 My partial goals are: Prototype 70cm RX and 2m TX Demonstrate above, with some form of SDX prototype Demonstrate prototype IHU-3 and CAN widgets Structure design and model Refine microwave phased array plans Peer review, test, demonstrate text messaging Begin development of integration plan and composite test plan Develop Work Breakdown Structure (WBS) leading to a preliminary development/construction schedule

The last item is clearly mine; Gould has been helping me on the WBS. Obviously, once I've laid it out, I'll need your comments and then some schedule estimates. I think that we are now at the point where it's time to define a schedule of what is reasonably achievable so that we can begin to make construction/integration/launch plans.

Please add to the goals; this is just my first cut.

Please also add to topics.

I've asked for help on my issue with EP; will advise as soon as the agenda is posted there.

Thanks & 73, Jim wb4gcs@amsat.org

---

Via the Eagle mailing list courtesy of AMSAT-NA Eagle@amsat.org http://amsat.org/mailman/listinfo/eagle