This is no WMD, but a German radio station transmitting current date, for time synchronization purposes.

I first stumbled upon DCF77 while working for CamTrace.
Some of our customers insisted on not connecting their video-surveillance network to the Internet.

The first solution coming to mind is to set up some NTP server. Which would work, most of the time.
Although, you should know NTP uses a stratum, keeping track of how high you are in the food chain. Having a lower value is critical, to allow other devices to synchronize their clock against yours.
Our consumers may restart their server, not fully understanding those concepts. But a client configuring his camera right after booting his server is not wrong. Thus, a good way ensuring your stratum is low enough so that devices may always accept what your NTP server is answering, is to get your time from a reliable source. Such as some german-kalität radio clock. Note this solution is only viable in the 2.000kms around Frankfurt though.

I’m mostly familiar with Axis networks cameras, but assume the problem presents itself on anything not embedding some RTC (like Raspberry Pi on default configuration, module being sold separately) : setting the date installing the device is a mistake, knowing it would fluctuate relatively quickly (worst cases, we’re talking about a few minutes per day, quickly adding up to hours, …).

Thus, I’ve combined some Raspberry Pi to a MouseCLOCK USB. NTP allows interfacing with such clock. A minimalistic /etc/ntpd.conf would look like this:

server mode 19
fudge stratum 0
fudge time1 0.042

Using as source tells ntp to look for /dev/refclock-0 device. Assuming FreeBSD, your clock device would show up as /dev/cuaU$x. Linux, /dev/ttyUSB$x. You may add to ntp startup the following lines:

if /usr/local/sbin/lsusb | grep mouseCLOCK >/dev/null; then
if test -c /dev/cuaU0; then
test -h /dev/refclock-0 || ln -s /dev/cuaU0 /dev/refclock-0

A cleaner way to create this link could be using devfs. In FreeBSD, add to /etc/devfs.conf the line cuau0 refclock-0.
On Debian, use udevd creating a file in /dev/udev/rules.d matching your device, like KERNEL==”ttyUSB*”, ATTRS{idProduct}==”e88a”, SYMLINK+=”refclock-%m”.

After a while, querying ntp should confirm proper synchronization:

root@cronos:/usr/ports # ntpq -crv -pn
assID=0 status=0264 leap_none, sync_lf_clock, 6 events, event_peer/strat_chg,
version="ntpd 4.2.4p5-a (1)", processor="arm",
system="FreeBSD/10.1-STABLE", leap=00, stratum=1, precision=-19,
rootdelay=0.000, rootdispersion=1026.460, peer=25445, refid=DCFa,
reftime=d8e8e24f.1ec18939 Mon, Apr 27 2015 18:29:03.120, poll=6,
clock=d8e8e25d.bb054ad7 Mon, Apr 27 2015 18:29:17.730, state=4,
offset=-77.794, frequency=472.839, jitter=10.929, noise=27.504,
stability=0.197, tai=0
remote refid st t when poll reach delay offset jitter
* .DCFa. 0 l 14 64 1 0.000 -77.794 10.929
root@cronos:/usr/ports #