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| To: | [email protected] |
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| Subject: | LF: Re: MSK tests |
| From: | "Vernall" <[email protected]> |
| Date: | Sat, 27 Nov 2004 08:26:15 +1300 |
| References: | <[email protected]> <[email protected]> |
| Reply-to: | [email protected] |
| Sender: | [email protected] |
Bill and others, ....... For example, at MS1000 thetotal frequency shift is only 0.50 Hz (+ or - 0.25 Hz away from the nominal800 Hz audio carrier freq) - and any mistuning seriously eats into our noise margins. That sort of tuning accuracy is awful hard for most folks to achieve. I think we need to draw a line in the sand as to what minimum stability is needed. Readily available gear with a 0.5 ppm TCXO master oscillator means the stability at the LF bands of interest is 0.1 Hz. I've been using a TS-850 for some years with a good 20 MHz TCXO (not the Kenwood SO-2 but a Rakon one with voltage fine tuning) and over a restricted temperature range like you get with a thoroughly warmed up rig I find the practical result is a lot better than 0.5 ppm. I've got external calibration sources better than 0.01 ppm and I've found that there is no need to tweak the tuning voltage on the '850 TCXO as it is very good from month to month. I'm also aware from reports from Mike ZL4OL that the Icom IC-R75 receiver fitted with the high stability oscillator can do better than 0.1 Hz from month to month once calibrated. So I suggest that for "serious DX" it should be assumed that each end could maintain frequency stability within 0.1 Hz. I'm not unhappy about others with less stable gear having a crack at slow rate digital modes, and adjusting things accordingly, but it should not impede software development that relies on tighter frequency stability. 73, Bob ZL2CA |
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