[time-nuts] Next Generation Time/Frequency Standards May Require Provisions Preventing Vertical Displacement

[Magnus Danielson]

On 09/30/2010 06:14 AM, jimlux wrote:
> Magnus Danielson wrote:
>>
>> Doppler effects is much more important, and it's effects is being
>> treated regularly, such as when talking in the GSM phone while driving
>> the car...
>>
> Hmm.. I think crystal oscillator frequency variation in the phone is a
> bigger factor. Let's say you're zipping down the road at 200 km/hr
> (55m/s), texting your friends. That's about 0.2ppm Doppler or around 400
> Hz (for a 2 GHz carrier).. as noted.. the XO probably has 1ppm (at
> best.. more like 10ppm)

On why there is a big market for small but stable TCXOs at 26 MHz.

> An even bigger problem in a mobile environment is multipath, which is
> far worse than the Doppler.. The effective propagation path distance
> could easily change 1000 meters in a fraction of a second.

Depending on system, different approaches to handle fading and multipath 
is done.

Cheers,
Magnus