In this month’s column, Nils Schiffhauer DK8OK keeps up with time. He tunes into Standard Time and Frequency (STF) transmissions, only to return from his time travels – with some surprises.

It was only three years after Guglielmo Marconi’s (1874-1937) first successful experiments to communicate wirelessly, that Howard Grubb (later Sir Howard, 1844-1931) had the idea in 1898 to use these Hertzian waves to transport time signals. However, it took another five years until the US Navy transmitted the very first time signal to control their ships’ chronometers.

This was another breakthrough in navigation, which, until then, had suffered from the problem of not being able to reliably determine the longitude of a position. Whereas latitude can be shot by a sextant at the highest angle of the sun, longitude is best measured by local time, or solar time, against a precisely known reference time.

Clockmaker John Harrison was the first to develop such a device from 1735, and in 1761 his H4 clock, with a diameter of just 5.2in was found to have been just five seconds slow, after it had sailed aboard HMS Deptford from Portsmouth to Jamaica within 65 days.

Today, the most precise time is brought to you by GPS and other satellites, which are ubiquitous, beaming to mobile phones, tracking bracelets and even wristwatches. GPS is unbelievably precise but needs more or less a direct line-of-sight to some satellites as well as a power-hungry chip.

Here, some land-based transmitters can step in, providing Standard Time and Frequency (STF) transmissions. The concept of radio-controlled clocks, as invented by Wolfgang Hilberg (1932-2015) made this technology accessible to all consumers, albeit after a noticeable time lag of some 20 years.

Only after the expiration of his patent of 1967 did the industry start to develop such clocks.

Radio Clocks Listen to Long Wave

Nowadays, you can barely avoid buying an alarm clock that is not radio-controlled by some station in the long wave frequency range, from 40kHz (JJY in Japan) and 60kHz (MSF in the UK), to 77.5kHz (DCF77 in Germany). These stations are run by a standard quartz clock, corrected one or more times by the time telegram from their integrated long wave receiver.

The signal this technology produces automatically changes from daylight saving time to winter time and introduces some delicate corrections like leap seconds.

Tuning is achieved automatically, which may sometimes be puzzling. For instance, during our recent holiday on the Baltic Sea, our alarm clock changed overnight (and unnoticed) from DCF77 to MSF, showing in the morning UK time, this being, of course, one hour behind official German time.

The overall accuracy of a radio-controlled clock like this is better than ±0.5s, which means that you can read the time, with an accuracy to around one second. This is good news for consumers, especially for the owners of the more than one hundred million radio-controlled clocks in Germany alone.

Users are also happy that the state-run transmissions of the German time signal have been secured until, at least, 2021. This is not self-evident, as HBG on 75kHz, a similar service from Switzerland, ceased operation by the end of 2011, after 45 years of sterling service. This was done only after it became clear that the radio clocks of Swiss consumers would seamlessly and automatically switch over to the German time signal.

Long wave is excellent in penetrating houses. It provides strong signals 24/7, within a transmission range of at least 1,500km. It can also be received with miniaturized ferrite antennas.

The image in Fig. 1 shows the levels of five different time signal stations over a period of 24 hours; DCF77 is the relevant station to control radio clocks. In the UK, MSF should deliver similar results.

Very low frequencies (VLF) under 30kHz even penetrate seawater, on a near-worldwide scale. Therefore, some CIS stations from Russia, Belarus and Kyrgyzstan make use of these wavelengths to disseminate time signals. These can be received by submerged submarines (Fig. 2).

On the other end of the long wave spectrum, you will find two radio stations that continuously carry time signal information for radio clocks. One of them (TDF) originates in Allouis (France) on 162kHz (Fig. 3) and the other one is, of course, BBC Radio 4 (Droitwich) on 198kHz (Fig. 4).

The French ceased to transmit the France Inter radio broadcast by the end of 2016, leaving the transmitter free to disseminate just the time signals for the more than 200,000 radio clocks in the country.

The days of the Droitwich transmitter from 1985 seem to be counted too, as analogue radio is considered, by many, to be rather obsolete. There are only ten spare valves left to keep the site working.

Both TDF and BBC transmit their time information via phase-modulating the carrier at such a small data rate (BBC: 25bps) that the ‘ordinary’ listener would not actually perceive it.

Of course, the transmission systems differ from one another:

http://tvignaud.pagesperso-orange.fr/am/allouis/allouis-heure.htm
http://downloads.bbc.co.uk/rd/pubs/reports/1984-19.pdf

A clear remnant of the past is the FSK time telegram of RAI, the Italian Radio, on medium wave. This is still broadcast just before the hour on 900kHz (Fig. 5).

Nearly all the time signal transmitters synchronize their frequency to the same rubidium or even caesium standard; hence their classification as ‘Standard Time and Frequency’ transmitters.

The US National Institute of Standards and Technology (NIST) has a detailed brochure, explaining how they (and others) generally work on VLF, LF and HF:

https://tf.nist.gov/general/pdf/1383.pdf

Globe-Spanning Short Wave

On HF, the frequencies of 2500, 5000, 10000, 15000, 20000 and 25000kHz are the assigned playgrounds for these STF stations. Some are still active and provide a good indication of HF propagation conditions.

Furthermore, some countries use odd frequencies, like Canada and Russia. They are the leftovers of a once quite vivid scene of stations spanning the globe from Australia (VNG, Fig. 6) and New Zealand (ZLFS), South Africa (ZUO) and India (ATA), to Peru (OBC) and Argentina (LOL).

These are gone forever – some together with their country of origin – (Fig. 7) and new time signal stations are popping up but rarely.

One of them is the Finnish MIKES station, serving a campus community on 25000kHz, with 100W. The station is sometimes heard all over Europe, when good Sporadic-E propagation conditions prevail.

Moreover, there is a somewhat mysterious Italian station (Associazione Amici di ITALcable) transmitting close to 10000 and 15000kHz in USB. It has time signals, music, SSTV and some pure hocus-pocus. www.associazioneitalcable.it

Software at the Right Time

Yes, there are standards for coding time, date and other information as well as ‘time’ itself. There are different artificial (man-made) scales for this, not to mention local time, daylight saving time and public holidays.

Most of this regulatory information is duly laid down in the BIPM Annual Report on Time Activities of the Bureau International des Poids et Mesures (The International Bureau of Weights and Measures) in Paris.

From here, the first European time signals were transmitted from the Eiffel Tower on a wavelength of 2,000m back in 1910.

www.bipm.org/utils/en/pdf/time_ann_rep/Time_annual_report_2016.pdf

It is only a slight exaggeration to say that there seem to be more standards than stations, as you may learn from the chapter on Time Signals in the above-mentioned PDF. Alternatively, have a look at this publication by the International Telecommunications Union (ITU). It lists some stations that have now faded out:

www.itu.int/dms_pubrec/itu-r/rec/tf/R-REC-TF.583-5-200105-S!!PDF-E.pdf

From a DXer’s point of view, monitoring time signal stations can offer the opportunity to distinguish co-channel stations (e.g. BPM, PPE and WWV/WWVH, all on 10,000MHz) from one another (Fig. 8).

Comparing several stations with a (software) oscilloscope will enable an observer to measure relative differences in the times taken for the signal to make its journey from the transmitter to the receiver (‘Time of Flight’).

I did this, in the case of 15,000MHz with the stations WWV and WWVH (Fig. 9).

The VOCAP software I used shows that the signal of WWVH would lag behind the WWV signal for about 16ms. This is the difference you can see in the image.

Some of the time signals can be decoded with software, which (in their licensed versions) can also synchronize your PC clock.

The RadioClock software by COAA, for instance, will synchronize your PC to a few time signals. Among them are both MSF and CHU.

www.coaa.co.uk/radioclock.htm

Moreover, there is the Clock program, as part of the highly-recommended MultiPSK software decoder. It covers most time signals. It is free, if you ‘just’ decode:

http://f6cte.free.fr/index_anglais.htm

The latter program is the accepted benchmark standard here, and it also works on remote receivers to, for example, decode Japan’s local time on JJY (40kHz) via an SDR in Kobe (Fig. 10).

List of Stations

The list of international time signals stations in Table 1 is based on my own monitoring in 2018.

Those stations I have checked via remote KiwiSDRs located in their service region, are marked with an asterisk (*).

www.sdr.hu

I am indicating the frequency, call sign, best reception in the London region in mid-October (as calculated by Rockwell-Collins’ PropMan 2000) and I have included some remarks.

The table is meant to give DXers the ‘best shot’. You will also find some links, many of them in English, some in the local language.

Some of the stations, however, may offer outdated information, or may simply not be available.

* Geoffrey Chaucer, Canterbury Tales, Prologue to the Clerk's Tale

Table 1: International Standard Time and Frequency (STF) Transmissions

Argentina
10000kHz* LOL Buenos Aires, scheduled only 14:00 – 15:00 UTC (reception unlikely in Europe throughout the year).
www.hidro.gov.ar/observatorio/lahora.asp?n=4

Belarus
25kHz RHJ69 Vilyeyka 07:06 – 07:25 UTC, 20 x CW ID at the start.
ftp://ftp.vniiftri.ru/BULLETINS/V/BulV_15_2015.doc

Brazil
10000kHz PPE Rio de Janeiro 17:00 – 08:00 UTC (peak 01:00 – 02:00 UTC), AM; every 10 seconds, there is a time announcement in Portuguese in the upper sideband.
www.horalegalbrasil.mct.on.br/RadioDifusaoSinaisHorarios.html

Canada
3330kHz CHU Ottawa 03:00 – 08:00 UTC, before each minute ID and time announcement in English/French and French/English.
7850kHz CHU Ottawa 16:00 - 12:00 UTC (peak 08:00 UTC); prior to each minute, there is an ID and time announcement in English/French and French/English.
14670kHz CHU Ottawa 10:00 – 19:00 UTC (peak 16:00 – 18:00 UTC), prior to each minute, there is an ID and time announcement in English/French and French/English.
www.nrc-cnrc.gc.ca/eng/services/time/short_wave.html

China
68.5kHz* BPC Shangqiu, scheduled 00:00 – 21:00 UTC.
www.time.ac.cn/serve/BPL.htm
5000kHz BPM Lintong 16:00 – 23:00 UTC, before each hour, a CW ID and announcement in Chinese are broadcast (Fig. 11).
10000kHz BPM Lintong 08:00 – 18:00 UTC, before each hour, a CW ID and announcement in Chinese are transmitted.
15000kHz BPM Lintong 05:00 – 09:00 UTC (scheduled 01:00 – 09:00 UTC), preceding each hour, a CW ID and an announcement in Chinese can be heard.
www.time.ac.cn/serve/BPM.htm

Finland
25000kHz MIKES-Otaniemi (try this under sporadic-E propagation, ‘short-skip’, conditions).
http://pdf.dzsc.com/88888/200842216119417.pdf

France
162kHz TDF-Allouis (24h).
http://tvignaud.pagesperso-orange.fr/am/allouis/allouis-heure.htm

Germany
77,5kHz DCF77 Mainflingen (24h).
https://www.ptb.de/cms/en/ptb/fachabteilungen/abt4/fb-44/ag-442/dissemination-of-legal-time/dcf77.html

Italy
900kHz (and other medium transmitters of RAI) during the periods of dawn and dusk.
http://ik1yde-segnaliemodulazionidigitali.blogspot.de/2011/12/segnale-orario-rai-fsk-33-bd.html
http://toi.inrim.it/uk/iensrc.html

10000 kHz Corsanico-Bagecchia, experimental (pirate?) station in USB 04:00 – 23:00.
15000 kHz Corsanico-Bagecchia, experimental (pirate?) station in USB 07:00 – 11:00 and 17:00 – 18:00.
www.associazioneitalcable.it

Japan
40kHz JJY Mt. Ohtakadoya (a challenge, best try this during their local sunrise, at around 20:30 UTC).
60kHz JJY Mt. Hagane (see above, plus only during a rare service break of MSF on the same channel) (Fig 12).
http://jjy.nict.go.jp/jjy/index-e.html

Korea (South)
5000kHz HLA Daejeon 15:00 – 20:00 UTC (can be distinguished from other signals, especially BPM, by its second-pulses of 5ms in length and of 800 milliseconds in length at each full minute).
http://slideplayer.com/slide/10583083/

Kyrgyzstan
25kHz RJH66 Chaldybar, 04:06 – 04:47, 10:06 – 10:47; 20 x CW ID at start (Fig. 13).
ftp://ftp.vniiftri.ru/BULLETINS/V/BulV_15_2015.doc

Russia
25kHz RJH90 Nizhny-Novgorod, 08:06 – 08:47, 20 x CW ID at the start.
25kHz RJH77 Arkhangelsk, 09:06 – 09:47, 20 x CW ID at start.
25kHz RJH63 Krasnodar, 11:06 - 11:40, 20 x CW ID at the start.
ftp://ftp.vniiftri.ru/BULLETINS/V/BulV_15_2015.doc

66.67kHz RBU Taldom (24h) (best during periods of dawn and dusk).
4996kHz RWM Taldom (24h) CW ID at xx:09/xx:39.
9996kHz RWM Taldom (24h) CW ID at xx:09/xx:39.
14996kHz RWM Taldom 05:00 – 19:00 UTC, CW ID at xx:09/xx:39.
ftp://ftp.vniiftri.ru/BULLETINS/V/BulV_15_2015.doc

United Kingdom
60kHz MSF Anthorn (Cumbria) (24h).
www.npl.co.uk/science-technology/time-frequency/products-and-services/time/msf-radio-time-signal
198kHz BBC-Droitwich (24h).
http://downloads.bbc.co.uk/rd/pubs/reports/1984-19.pdf
 

USA-Colorado
60kHz* WWVB WWV Ft. Collins (24h).
www.nist.gov/pml/time-and-frequency-division/radio-stations/wwvb
5000kHz WWV Ft. Collins 05:00 – 09:00 UTC, time announcement before each minute (male).
10000kHz WWV Ft. Collins 11:00 – 14:00, 18:00 – 20:00, time announcement before each minute (male).
15000kHz WWV Ft. Collins 13:00 – 18:00 UTC, time announcement before each minute (male).
www.nist.gov/pml/time-and-frequency-division/radio-stations/wwv

USA-Hawaii
5000kHz WWVH Kekaha 04:00 – 05:00 UTC, time announcement before each minute (female).
10000kHz WWVH Kekaha 00:00 – 17:00, (peak 06:00 – 07:00 UTC), time announcement before each minute (female).
15000kHz WWVH Kekaha 15:00 – 18:00 UTC, time announcement before each minute (female).
https://tf.nist.gov/stations/wwvh.htm

Editor’s Reading Tips

Jespersen, J. and Fitz-Randolph, J. (1999) From Sundials to Atomic Clocks – Understanding Time and Frequency (Mineola, NY: Dover Publications; ISBN-13: 978-0-486-40913-9)

https://tinyurl.com/y8zytkhe 

Klawitter, G. (1992) Zeitzeichensender – Time Signal Stations (Siebel)

Lombardi, M. A. (2002): NIST Time and Frequency Services (NIST Special Publication 432, see main text)

PTB: Special Topic: 50 Years of Time Dissemination with DCF77 (Newsletter 119 (2009), No. 3)

https://tinyurl.com/yagongd5 

From the RadioUser Archive: Radio in Space and Time: Time Signal Stations (RadioUser, October 2012: 8)

This article was featured in the October 2018 issue of Radio User