In Japan there are radio-controlled clocks. Time is synchronized by 40khz (in west Japan) and 60khz (in east Japan) radio, which is broadcast from transmission towers. The signal is known as JJY:

https:/ /en.wikipedia.org/wiki/JJY

After the earthquake in 2011, the tower in the east Japan was collapsed. Time synchronization in the east Japan is affected. Hence, someone Japanese has made a simulators and shared on the Internet.

I am from Hong Kong. I have a radio-controlled watch and clock bought from Japan. I want my devices to be synchronized. There are iOS and Android app JJY-simulators. I have tried some of them. This one works well:

https:/ /play.google.com/store/apps/details?id=jp.houryo.jjyemulator&hl=ja

The principle behind is, using time from NTP server, emulating the JJY signal, sending out through 3.5mm audio port.

Now I want to implement the emulator on a Raspberry-Pi. There are some tutorials found on the Internet. Below is the one I am following to:

http://itpro.nikkeibp.co.jp/atcl/column/14/093000080/093000002/?ST=oss&P=1 (Japanese)

Instead of the source-code in the tutorial, I use this one: https://github.com/snt/rpi_jjy_server


I have made the circuit following the tutorial:

However, most of the time my watch does not read any signal. If there is signal, the signal status is "low", and eventually the time-sync is failed. (For the Android-app one, my watch can read a "high" signal.)

Note: I am using Toshiba 2SC1815-GR transistor, 30k ohm resistors, which are suggested in the Git-hub article. And a telephone-line made antenna.

I have tried using a 9V battery replacing the 5V Raspberry-Pi power source. But it does not help.

My knowledge on electronic is very limited. Please kindly forgive me if I have asked silly questions or made silly mistakes. Could anyone please point out if I am made anything wrongly? Or, by what means could I boost the signal from the antenna?

Great appreciation for any help!

  • \$\begingroup\$ Personally I would just reverse-engineer the antenna for the smartphone. use an oscilloscope to check the signal and try to reproduce it. But my first thought is.. The antenna look quite different. Did you try to attach the 3.5mm antenna to the ciruit to see if it works? \$\endgroup\$
    – frarugi87
    Dec 2, 2015 at 9:22
  • \$\begingroup\$ The 3.5mm antenna is the same with the one I am using on the Raspberry-Pi. They are the twisted-wires inside one telephone line. And I did try using the 3.5mm one on the Raspberry. It does not work. (Actually does the antenna really work with only one end connected onto the breadboard?) An oscilloscope is too expensive for me, as I am just a beginner working on this just for fun. \$\endgroup\$ Dec 2, 2015 at 9:32
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    \$\begingroup\$ Thanks for your comment. I have no idea on "electrically-coupled" and "magnetically-coupled" antennas. Let me have some research for understanding first! \$\endgroup\$ Dec 2, 2015 at 9:44
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    \$\begingroup\$ At these low frequencies I think a magnetic loop antenna works better, see my answer. \$\endgroup\$ Dec 2, 2015 at 9:45
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    \$\begingroup\$ The article said: Find a vinyl line with 1x-cm to several meters, make a loop, place it near to a radio-controlled clock; Place one end onto the breadboard. 最も簡単なのはGPIOでLEDを点灯する回路を作り、LEDとトランジスタのコレクタの間からビニール線(数十センチから数メートル程度)を引き出して、その線をぐるぐる巻きにしておくというものでしょう。その「アンテナ」を電波時計の近くに置きます。ぐるぐる巻きにしたビニール線は、テープで輪が解けないように止めておきます(写真5)。ビニール線の一端をむき、ブレッドボードの穴に刺さる程度の太さに芯線をまとめてください。銅単線を使うともっと楽かもしれません。 So I believe the original set-up should work? \$\endgroup\$ Dec 2, 2015 at 11:24

1 Answer 1


"Actually does the antenna really work with only one end connected onto the breadboard?" No, not this type of antenna. What you have is a loop antenna and it creates a magnetic field. You're now using it as if it is an electrical antenna and that would work IF it was very long, for 60 kHz we're talking 1250 meters (!!!) and not rolled up like yours.

I suggest you connect the open end of the antenna to +5 V BUT to limit the current, use a series resistor of value 1 kohm or so.

If you build this then I think there's a good chance it will work. Note how the Antenna is a coil (long wire with many turns) and both ends of the wire are connected !


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ Thank you for your answer. I am sorry but my knowledge is limited. Is the physical shape of the antenna, or the way of connection decides the form (electrical / magnetic) of the antenna? \$\endgroup\$ Dec 2, 2015 at 10:22
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    \$\begingroup\$ Antennas, that is a difficult subject ! Antennas emit EM waves so both electric and magnetic. However for some types the magnetic field is stronger, for others the electric field. That might also be related to how you connect it. Usually one-side connected antennas are electrical and two-sided with a conductive connection (like yours) are magnetic. \$\endgroup\$ Dec 2, 2015 at 10:35
  • \$\begingroup\$ So, since I am connecting one pin only, making the antenna work as an electrical one, limiting the current with 1k ohm resistor would make the signal "better" without making the length of the antenna longer, right? \$\endgroup\$ Dec 2, 2015 at 10:57
  • \$\begingroup\$ How about if I want to make the antenna into a magnetic one, do I need to modify the hardware, or the code? \$\endgroup\$ Dec 2, 2015 at 10:58
  • \$\begingroup\$ The 1 kohm resistor is needed to limit the current as your antenna loop is essentially just a long wire. Just do as I suggested, connect the open end of the antenna to +5V through the 1 kohm resistor, that is all you need to do. You are using a loop antenna, it is supposed to work as a magnetic antenna. There is no need to change your code. \$\endgroup\$ Dec 2, 2015 at 11:27

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