[time-nuts] signal transit time through WWV receiver

[Magnus Danielson]

Hi,

On 2020-01-06 22:11, Hal Murray wrote:
> ashtongj at comcast.net said:
>> Are there any simple tricks to measuring the transit time. My thought is to
>> create a pulsed 10 MHz source, with AM modulation when the signal is on, and
>> compare a path directly into one channel of an oscilloscope with the audio
>> output of the receiver feeding into the other channel. Any easier or better
>> suggestions? My test equipment is much more limited than many other members
>> of this list. 
> You will need a filter to detect the AM modulation.  That filter will have a 
> delay.
>
> Is there any difference in delay between an analog filter and a digital filter?
>
> How do the wizards that use common view GPS time transfer calibrate the delay 
> through their filters?
>
It is common to calibrate and compensate for at least the input of the
receiver, so whatever offsets the receiver introduces is removed in
presented time. There will be a residue offset which is often measured
and compensated for by other means. Then, antenna and antenna cable
similarly needs compensation. For GPS, the phase center of the antenna
becomes compensated by the positioning, but this isn't perfect that that
is ironed out in post-processing typically. Quality of antenna, receiver
and installation is know to affect things, especially due to multi-path.
For WWV type of receivers, there is no in-system compensation of
propagation delay, so that will have to be done using other means, such
as GPS or as in the old days, phase is transported by means of a stable
atomic clock. Once arrived home, the delay is jotted down and wheeled
into the delay compensation of the clock.

Regardless, with GPS most of this comes with decent enough compensation
as it is and if you care about phase to the ns you calibrate everything
and then calibrate again. Oh, phase-stable cables becomes an issue then.

Cheers,
Magnus