[ntp:questions] ntpd: time reset problem

David J Taylor david-taylor at blueyonder.not-this-part.nor-this.co.uk.invalid
Fri Sep 18 13:23:24 UTC 2009


"David Lord" <> wrote in message 
news:7hh1ihF2smeuvU1 at mid.individual.net...
[]
> It's very wet round here with 90 +/- 10% R/H being common in
> various locations including out back of house which is often
> 95%. You could only hang washing out for it to get wet. This
> means leaves are soaking wet and beginning of year when I
> swapped from BR304 to GPS18-LVC I was getting continuous
> reach 377 but this deteriorated as trees came into leaf.

Ah, I thought you were in the UK.  The 18x LVC is a lot more sensitive 
than the 18 (without the x), for your information.

> Datasheets on some receiver chips seem to use just a crystal
> but some seem to have some coupling back from output to input
> but it's not clear if feedback or forward. Otherwise all trf
> with agc from a peak detector but filtering time constants
> aren't easy to work out as just giving a suggested capacitor
> value.
>
> I tried similar interstage crystal coupling which produced a
> good oscillator until receiver module was shielded and moved
> away from aerial. That also lost me some of timecode pulses
> as not enough damping.

One of the times when designing by impulse response (of the envelope) 
rather than just bandwidth!

> Maplin circuit I have shows the fast timecode but more recent
> documentation from NPL doesn't mention any fast code and the
> slow code shown is different to that given with the Maplin
> circuit.

The fast-code signal was dropped in October 1998.

> I've seen widely different values used for filter of the
> NE567 from about 1ms upwards. Maplin design seems to be
> for loop filter of NE567 with bandwidth of about 8kHz
> (depends on input level) and 1ms with option of extra
> capacitor at input of Schmitt to give about 15ms to
> remove fast pulses.

I still think that nothing beat filtering as early as possible, in the 
detector stage it's rather last gasp.

> I'm suspecting I've something broken on my demodulator
> pcb so will be rebuilding with added 4093 and couple of
> pots to try different time constants. That's just a
> challenge since Conrad module with 60kHz crystal is
> tiny, low power and works ok.
>
> The Conrad module doesn't give a 60kHz output though and
> my aim was to use that as frequency reference same as
> Andy Talbot (G4JNT) design.
>
> David

Ah, I once thought of doing something similar with the 198KHz (was 200KHz) 
signal from Droitwich.  Clever chaps those who design the modules - as you 
say, they do work well.

73,
David 




More information about the questions mailing list