OK0EPB - 7 039,4 kHz
Exact Pendulum Beacon
- Transmiting schedule
- The Pendulum Squadron
- The Czech time radiobeacon driven by pendulum
- The time signal of OK0EPB is generated by a pendulum with a rod made of fused quartz.
- The clock's machine works on the basis of Froment's system with a constant impulse. (take a look here)
- The maximum difference of time signal is held in the tolerance of 0.1 sec.
- The beacon output power of TX is 10 (ten) W to dipole @22m.
Beacon is transmiting 100 ms dots every seconds, without transmiting call, foF2 frequency and number of UTC - this is 12 WPM CW. In full minute transmit dash after five dots.
.........OK0EPB.........foF2...........UTC HHMM .....- | | | | | | | | | | | | 10 20 30 40 50 60 sec
As the ionospheric F layer is playing most important role in shortwave propagation, critical frequency of its higher part, f0F2 as main parameter was choosed for sending by OK0EPB beacon (roughly half minute after time signal)..
The F layer (or better F region), also known as the Appleton layer extends from about 200 km to more than 500 km above the surface of Earth. It is the densest point of the ionosphere, which implies signals penetrating this layer will escape into space. At higher altitudes the amount of oxygen ions decreases and lighter ions such as hydrogen and helium become dominant, this layer is the topside ionosphere. Here extreme ultraviolet (UV, 10–100 nm) solar radiation ionizes atomic oxygen.
The F layer consists of one layer at night, but during the day, a deformation often forms in the profile that is labelled F1. The F2 layer remains by day and night responsible for most skywave propagation of radio waves, facilitating high frequency (HF, or shortwave) radio communications over long distances see http://en.wikipedia.org/wiki/Ionosphere
In our case f0F2 measurements from station Průhonice near Prague are used http://digisonda.ufa.cas.cz not only because this ionosonde is close to the beacon QTH, but also for high quality and reliability of measurements. They are made every 15 minutes, f0F2 in MHz is ready for sending after 6 minutes of processing, therefore message sent by OK0EPB is changing every sixth, twenty-first, thirty-sixth and fifty-first minute of every hour.
Critical frequency f0F2 value use:
- Below f0F2 we have just dead zone in Central Europe.
- Multiply f0F2 by M factor we can obtain Maximum Usable Frequency = MUF. For higher frequencies than MUF radiowaves over Central European region are not returned back to Earth, therefore higher bands are closed. Usual value of M factor is near 3. For example - by f0F2 over 9 MHz is good chance of 10 meter band opening.
Pendulum is enclosed in a vacuum chamber (by www.vakuum.cz) to avoid the impact of changes in atmospheric pressure. Infra red sensor detected position of pendulum. Moments when pendulum passes middle position are registered by the software, which also generates driving pulses for the coil and beacon keying.
2013-04-15 - During the vacuum chamber reconstruction the time signal is hold +/- 1 sec. (Edit)
2012-12-28 - Antenne repair(Edit)
Our aerial was repaired after roof reconstruction by OK1CW - VY TNX, DR Vlada !!!
2012-09-02 - Change time schedule(Edit)
2012-08-14 - Earthquake(Edit)
in sea of Okhotsk (49.784°N, 145.126°E) with magnitude 7,7
Seismogram from Prague
2011-12-21 - Dependence frequency error on air pressure(Edit)
between 15 and 21 Dec 2011 (when the pendulum has not yet been placed in a vacuum chamber)
2011-12-13 - Results of G3PLX measurement(Edit)
Here attached is a good record from last night. The channel was clear of the Sura ionospheric radar which has been there for a week or so. This shows two shift pulse events, with the pendulum running about +3ppm between them. The 60mS point on my graph is the same point as the 0 mS point on your Phase graph. The 60mS difference is made from (1) 50mS because you measure the start of the dot and I measure the centre, (2) 4mS because I am 1200km from Prague, and (3) 6mS which we think may be the key-click filter in your transmitter.
- Frantisek OK1DF - Founder and the mastermind
- Petr ex OK1IRG - Software developer
- Jan OK2ZAW - Beacon hardware
- Peter G3PLX - Invaluable assistance
- Dan OK1HRA - IT & webmaster
- Vlada OK1CW - antenne system
- Frantisek OK1HH - beacon coordinator, propagation forecaster (foF2)
- Tom, OK1URT - wire and connectors expert