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No attempt will be made to change the physical 200 MHz clock to something else that is changeable, so phase noise is not affected. The Xylo will measure, the PowerSDR software will use the data to correct it's internals, resulting in very accurate, and stable frequencies with minimal changes to the existing hardware
That is my understanding on what the game plan is.
At 10:02 AM 12/31/2005, Philip M. Lanese wrote:
Tim, Eric2, et al
You can enclose the oscillator can within a thick block of material that has high thermal resistance (high thermal inertia). You do not want to have air moving around the oscillator because the heat conducted away from the oscillator will vary as the air flow varies and that effect will make the problem worse. This technique assumes you can safely heat the crystal to a good margin above any maximum ambient. In order to heat the crystal, you need to know the CRYSTAL turn-over temperature, a specification not usually available for 'canned' oscillators, or you could end up frying the oscillator that is also inside the can or over stressing the crystal itself, in which case it will go PERMANENTLY off frequency and ready for the round file. Most likely when you are about to make that once-in-a-lifetime DX contact.
You may reduce drift somewhat but the whole question of frequency stability and accuracy is: does anything you do matter if the various other ends of the communications circuit are not at least as stable as your end AND there are no variations due to propagation effects of the signals. Take EME at and above 432 MHz as an example. No matter how accurate and stable your frequency or that of your QSO partner, you still have to use your RIT to chase the returning echoes because of changing Doppler shift. WSJT's EME mode 65C is no longer used much, if at all, because it depends on the INCOMING signal, as well as your receiver, being stable within 5 to 8 Hz or so over an entire EME receive period. Really serious EME operators use Linrad because they can SEE the incoming signals' drift in 'real time' and can use the RIT when necessary to manually correct for frequency change.
You also have to remember that canned oscillators are 'consumer' products and the manufacturer can only invest so much in frequency stability, accuracy, reduced phase noise, etc. before he prices the product out of the market.
Any quickie after-market adjustment would at best be a 'one-off' and what are the chances of replicating a one-off 'fix' many times over.
If you want extreme accuracy, you have to start from scratch and go thru the whole (non trivial, not inexpensive and definitely time consuming) design process. That's just for the oscillator. Then you have to design temperature stable buffer circuits to insert between the oscillator and the load to effectively isolate the load, as well as other problem sources, voltage regulator noise, RF, etc., so the oscillator is not affected.
Then, as Jim, W6RMK, and others have pointed out, you turn your attention to 'fixing' the PC oscillator, the sound card oscillator, the OS software and the application software as needed.
Phil, K3IB
- ----- Original Message -----
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- Folks
- Yes, Bob N4HY mentioned on Teamspeak that he had 'insulated' the osc with some material which cut down on drift. Perhaps he could elaborate a bit more on the scheme he used.
- Eric2
Cecil Bayona
KD5NWA
www.qrpradio.com
"I fail to see why doing the same thing over and over and getting the same results every time is insanity: I've almost proved it isn't; only a few more tests now and I'm sure results will differ this time ... "
