Re: [IRCA] frequency measurement accuracy (please delete if not interested)

[Barry McLarnon <bdm@xxxxxxxxxx>]

On Tuesday 05 September 2006 01:19, Nick Hall-Patch wrote:
> >I wonder how much drift there is in the R8? Were you to tune to 10,000.400
> >and use Spectran to calibrate the R8 against WWV, how long does it take
> > for the R8 to drift 1 Hz? 2 Hz? How long had the R8 been on and been
> > stabilizing before the 2 numbers were taken?
>
> Last post, I promise....

Why the apologetic tone?  This topic is certainly relevant to this list, and 
if more DXers became familiar with frequency measurement techniques, it would 
benefit us all.

>  From a cold start, the R8 drifted about 8 Hertz over an hour when
> tuned to WWV on 10MHz, with most of that in the first 30 minutes, but
> from then on it's pretty stable, with bouncing around of about +/-
> 0.1 Hz.  (This according to Spectran)  10 MHz seems to be a worst
> case, and I'd never try measuring frequencies up there anyway, as you
> can see the smearing of the frequency presumably from Doppler shifts
> due to ionospheric movement.

I tried the same thing with my R75.  I have an excellent reference signal 
available, as CHU is just a few km away from me.  Accuracy of their carrier 
frequency is said to be 5 x 10E-12 (your mileage may vary if you're out of 
groundwave range!).  From a cold start, my measurement of CHU at 3.330 MHz 
drifted about 5 Hz in the first hour.  In the second hour, the drift was just 
under 1 Hz, and after that I could not detect any change (drift < 0.1 Hz).

BTW, I see plenty of the smearing from Doppler spreading in the MW band, most 
notably on TA signals in the high end of the band.

> KSL-1160 in comparison was at 395.55 Hertz (uncorrected) after the R8
> being on an hour, and seven hours later had not budged.  (compare
> that also to the 395.54 Hertz measured a few days previously, though
> believe I used a slightly more coarse FFT resolution for that
> one)  Drift does not seem to be much of an issue, surprisingly, at
> least after an hour of warmup.

That seems to be true of the R75 as well, but to be on the safe side, I 
usually leave it on 24/7.  It's also worth noting that another possible 
source of drift is the clock oscillator of your sound card (or on-board sound 
interface) in your PC.  I would expect similar warmup issues as with the 
receiver.  The PC I use for measurements is also on 24/7, so I haven't looked 
at that angle.

In any case, frequent checks against available reference signals is always a 
good idea.

Barry

-- 
Barry McLarnon  VE3JF  Ottawa, ON
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