Time Signal Reception with RTL-SDR USB Dongle in Europe?

Question

How can I receive a time signal with an unmodified RTL-SDR USB TV Dongle here in Europe?

RTL-SDR Dongles are able to receive the frequency range 52-2200MHz.

Here in Europe, radio-controlled clocks receive DCF-77, a time signal broadcast on 77KHz, but as 77KHz is a bit lower than 52MHz, that's out.

The GPS L2 signal is at 1575.42 MHz, so that's within the dongle's range, but the signal is way too weak to be received with the TV antenna. An active GPS antenna is needed, and for providing the antenna with the power, I'd need to make some modifications to the electronics which I don't really want to do.

In the old age of analog TV broadcasting, we had Teletext / Videotext here in Germany, which contained a time signal, but these times are long gone.

ADS-B reception with a dongle works like a charm, but unfortunately they did not put in time or date bits into the data packets.

So: Does anybody have any idea where in the spectrum that can be received by an unmodified RTL-SDR dongle there is a time signal that could be easily decoded?

I'm well aware that getting time over the network via NTP, or via a GPS modem via NMEA 0183 would be way easier, but I'm curious and just want to play around with that dongle a bit. Precision is not important. +/- 2 seconds is fine. And I'd like to do it the SDR-way, so using the dongle in the originally intended way (as a DVB-T receiver using the original software) defeats the purpose (i.e. learning and DIY)

Answer 1

The GPS L2 signal is at 1575.42 MHz, so that's within the dongle's range, but the signal is way too weak to be received with the TV antenna. An active GPS antenna is needed, and for providing the antenna with the power, I'd need to make some modifications to the electronics which I don't really want to do.

Well, first of all, GPS is really weak, but it still works under the noise floor; that's something important to realize – I've seen it more than one time that people are worried because they can't see GPS on a PSD display. You won't; you'll need signal processing to recover it from all the noise.

The modifications aren't all that complicated; basically, you need a capacitor to let through the AC component to the RTL dongle, and a voltage source to feed the active antenna; the required component is usually called a bias-T.

Nevertheless, an active antenna will be necessary – your RTL dongle probably won't have a Noise Figure low enough to receive GPS signals on its own.

In the old age of analog TV broadcasting, we had Teletext / Videotext here in Germany, which contained a time signal, but these times are long gone.

True; haven't looked at local FM stations, but RDS might be the way to go – it can contain a clock/time signal; the German Wikipedia claims that mainly publicly owned stations transmit that information field.

Have a look at gr-rds; it's a GNU Radio implementation of the Radio Data System. If you don't have a working GNU Radio installation (yet), you might try out the GNU Radio LiveSDR Image, which contains a ready-to-use gr-rds.