LF: Re: MSK tests

["Vernall" <vernall@xtra.co.nz>]

Bill and others,

> .......  For example, at MS1000 the
> total frequency shift is only 0.50 Hz (+ or - 0.25 Hz away from the 
> nominal
> 800 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