The Advantages of Crystal Control

Radio Record, Volume IV, Issue 33, 27 February 1931, Page 5

The Advantages of Crystal Control

Synchronised Programmes

] AS recently reported, crystal control has been installed at 3YA and various alterations haye been effected at the studio. The policy of the R.B.C. is to keep the transmitting equipment and studios of their stations completely up to date, and to that end additions and alterations in accordance with the best practice are continually being: made, It is quite two years since crystal control was installed at 2YA, and this _is indicative of the policy of the Broadeasting Company, for, apropos this, the latest news which the company has reeeived from America shows the development in that country of automatic crystal control. Most broadcasting stations in the United States are maintaining their frequency within 100 to 200 cycles of their assignments. In a country like America, where the air is crowded with stations, it is of vital importance that frequencies should be strictly adhered to. The development of commercial equipment maintaining carriers within five or ten cycles of a given frequency is a matter of the utmost economic importance in Hurope and America, where the number of broadcast stations to be accommodated is considerably greater than the number which can be accommodated on the available channels. As the standards of frequency control continue to improve, the day is approaching when carrier differences between stations on the same channel will be below the audio range, eliminating heterodyne interference where carriers overlap. Experiments in Synchronisation. At the same time that progress is being made toward independent local sources of stable carrier frequencies, steps are being taken for an exhaustive experiment to learn the effects of phase distortion occurring

from the reception of two stations, the carriers and programmes of which are synchronised. The synchronisation method employed will be the transmission of carried frequencies and programmes over wire lines, and means will be provided for altering the phase relation between the audio components of the two stations. Four leading stations of the National Broadcasting Company system, WHA, WIZ, WBAL, and WTIO, are participating. WHAF and WJZ are of 50,000 and 30,000 watts power, respectively, located near New York City, and enjoy full time operation on clear channels. WTIC, Hartford, Conn. and WBAL, Baltimore, MD., on the other hand, share a cleared channel, which each uses on alternate days. In order to permit the simultaneous operations of both of these stations, each will synchronise with one of the New York stations during that period when it would normally be standing-by for the other. WTIC, in Hartford, will synchronise with WHAF, a distance of about 108 miles, while WBAL has the use of the cleared channel. On the other hand, when WTIO is entitled to use the cleared channel, WBAL will synchronise with WJZ, a distance of 140 miles from Baltimore. The reason that this experiment is particularly significant is that the listener will be able to hear each of the stations with and without synchronisation. The availability of a comparison makes it possible for the uninitiated to pass judgment upon the effect of synchronisation upon quality. Furthermore, the experiment affords two ratios of local to distant signals of significant values. The high quality service area of WTIC and WHAF overlap, and are of equal and substantial value at many points. On the other hand, WBAL is but 10,000 watts and 140 miles from WIZ, so that almost any ratio of field strength difference can be observed.