On 15/11/2005 11:15 PM, Doug McLaren wrote:
In article ,
Falky foo wrote:

| rig it to your car and drive around resetting everyone's clocks!
| that would be a hoot!

It would, but there's a few problems --

1) It would probably qualify as harmful interference and would
probably annoy the FCC, no matter how low your power. (On the other
hand, it would be next to impossible to pin it on you unless your car
had some massive antenna array on top.)

(Sidenote: with an appropriate antenna and 100 watts, you could
probably reprogram the clocks in the entire city. Though a sutiable
antenna could be very difficult to come by, since 1/4 wavelength =
1250 meters.)

2) most of those clocks only sync up a few times per day (and often
only at night), and almost all of them require several `cycles' (and
each cycle lasts a minute) to do so. So you'd have to catch them
right when they're syncing up, and they'd have to receive your signal
the entire time.)

And if the clock does continuously re-sync, then it will go back to
the correct time signal the moment it stops picking up your signal.

But yes, it could qualify as a good `hack' if done properly.


Yup, this is a good example of a "data poisoning" hack. For those
receivers that only sync up to a single source (and with the caveats you
mention regarding when and how such receivers sync up) this is a
definite hack.

For those of us who rely on upstream NTP sources for their computers,
that protocol is relatively more robust. Even if some of the so-called
upper strata servers use WWV (or local equivalent) to get their time,
the protocol is designed to rejects times that obviously out of sync
with others. So those coincidental upper strata sources would have to
sync up at the same time to these radio sources for it propagate. I've
seen my local NTP server reject entire subnets because it was a few
seconds off. Eventually those subnets are trusted again.

Recently, wasn't there a problem with some of these signals? I recall
that folks who have those fancy set-themselves watches did not have
accurate time for a few weeks.