Nbs

The high frequency services of WWV arid WWVH are of most importance to U.S. amateurs t We are all aware of their usefulness for time and frequency spot checks. Actually there rtre eight technical serv ices provided by H F

NBS stations. The services of most interest to Hams are the standard audio and radio frequencies, time announcements, propagation forecasts and geophysical alerts.

Standard audio frequencies of 440 and 600 Hz are broadcast by WWV and WWVH. The 440 Hz note is the standard A above middle C for the music industry. The audio frequencies are transmitted alternatively at five minute intervals starting with the 600 Hz tone on the hour. The first tone period transmitted by WWV is three minutes long, with the remaining periods being two minutes in length.

A i WWVH tone periods are three minutes in length. The pulse or "Tick" consists of five cycles of 1000 Hz tone from WWV and six cycles of 1200 Hz tone from WWVH.

Carrier stability is maintained within five parts in 10u (which amounts to an error of 0.00005 Hz on the 25 MHz carrier). The transmitter's oscillator is correlated u ith the Cesium standard at NBS-

Propagation notices are transmitted during

A typical VLF receiver and correlator for submarine installation. This unit is built by Interstate Electronics for use on nuclear submarines. The receiver electronically compares a precision standard oscillator in the missile in* strumentation timing system with the VLF signal. Accuracies of three parts in 10 billion are easily obtained in a few hours of observation.

the last half of every fifth minute of each hour. The forecast is transmitted in MCW. The following scale is used.

1 Useless

2 Very Poor

3 Poor

4 Poor to Fair

5 Fair

6 Fair to Good

7 Good

8 Very Good

9 Excellent

Signals classed between 1 and i are called disturbed" (\Y), 5 is unsettled" (V) and 6 through 9 are "normal" (N), A forecast consists of a letter and a number. The letter designates current propagation conditions while the number is the forecast for the next six hours. An example would be U 7. T his would mean that current conditions are unsettled, but that they are expected to improve to "good" within the next six hours.

During the International Geophysical Year (1957-58) a series of geophysical alert symbols w as established to provide a world w ide warning system for events of geophysical siirnifi-cance* The following symbols are used:

C Cosmic rav event E No alert M Magnetic storm N Magnetic quiet Q Solar quiet S Solar activitv

W Stratospheric warning

These signals are transmitted in code 19 minutes after the hour from WWY and t9 minutes after the hour from WWVH,

You have probably heard a "burring*' sound while listening to WWW This is a special time code transmission ot Universal Time (UT). It is broadcast for a one minute period ten times an hour only on WWW The main use of this code is for standardizing time at observatories and missile test ranges. The code consist of a 100 PPS 36 bit serial pulse train containing day of year, hour, minute and second. To record this time signal you need an oscillograph recorder connected to the output of your receiver. A detailed description of the code, and the various high frequency services, is contained in National Bureau of Standards Miscellaneous publication 236 which is available from the Superintendent of Documents.

Foreign standard transmissions

Foreign standard transmissions aren't well known in the U.S. Many of them in the HF range share frequencies with WWY and WWVH. They are plagued with illegal trans-

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