http://www.livefromthehamshack.tv/2017/07/03/episode-104-elecraft-forum-presentation-hamcom-2017/ ----------------------------------- David, KG6IRW, from Elecraft at the 2017 ARRL West Gulf Division Convention, known as Hamcom. In this presentation, he talks about the new KPA1500 amp, the history of the K-line and KX-line radios, and what the company has learned from the many DXpeditions on which Elecraft has been represented.
Not mentioned is how the new synthesizers introduced 0.4 Hz sawtooth variations in frequency to keep the SI570 "low phase noise output" calibrated to the master oscillator. The frequency constantly drifts between corrections. It is not corrected by the XREF.
0.4 Hz? That's pretty low freq. Would those variations be noticeable to the average ham user? If so, in what way? Just curious -- don't have enough experience in this area to know...
The way I understand it, this is called "jitter", and it is present in ALL synthesizers that are phase locked to a master oscillator. "Jitter" is what causes phase noise, and the jitter and phase noise in the K3s is EXTREMELY low, among the lowest values in all transceivers, even rigs that cost more than double the price of a fully loaded K3s. Look at the "LO noise" values in the tables on Rob Sherwood's website for verification. Do I have this wrong, or am I missunderstanding something?
Phase noise varies with frequency. The extremely low phase noise of the new synthesizers occurs at RF frequencies. This jitter is of very low frequency and apparently doesn't "count"-- unless you're trying to measure frequency to less than 1 Hz. Then it drives one nuts. I'd like to see a full frequency range phase noise plot from .0001 Hz upward.
https://en.wikipedia.org/wiki/Phase_noise https://en.wikipedia.org/wiki/Jitter For those people with short attention spans: http://blog.bliley.com/ultimate-guide-to-phase-noise
Perhaps a pix of what is going on would help. Attached is a .jpg showing the K3 pitch in CW mode vs time. Two things are shown: the overall RX drift and the sawtooth variation introduced by the SI570 synthesizer outputs. Drift which is a reflection of the TCXO is about 0.19 Hz/hour. The SI570 sawtooth slopes are about -7.9 Hz/hr-- 50x greater and in opposite direction. There has to be a continuous renormalization of SI570 frequency to the master oscillator because it drifts like crazy. The jumps are the renormalizations. Yes its output is pure but drifty. The old synthesizers showed a smooth drift but none of the sawtooth jumps. Elecraft knows about this and in their opinion the reduced phase noise is a worthwhile trade off vs stability. Needless to say these jumps complicate using the K3 in frequency measuring tests where on is trying to come within 0.1 Hz accuracy. Note: This curve is a mild example and represents a well warmed up condition. Jumps as large as 0.4 Hz or more are seen under less thermally stabilized conditions.
Thanks for the graph Brian, it illustrates very nicely exactly what the synthesizer is doing, although I understood this before you presented the graph. Again, this happens with ALL oscillators that are locked to a reference source, the alternative would be to allow the oscillator to drift in frequency, which would introduce a whole new set of problems. As you indicated, Elecraft stated that their design was a worthwhile trade-off for the lower phase noise, which is a benefit for MOST users of the K3s. It seems that you want to utilize your K3 for something that is an extremely small niche of the total market, I doubt that ANY manufacturer is going to accommodate you in this regard. Measuring frequency to .1Hz is in the realm of laboratory grade test equipment, not amateur transceivers. In my opinion, Elecraft has the best amateur transceiver, BY FAR, in the K3s. 73, Dennis
