Radio age (Jan 1927-Jan 1928)

RADIO AGE for July-August, 1927 New Modulation is Biggest Radio Discovery in Twelve Years WHAT is regarded as the most radical radio discovery since the appearance of the three element tube, is an announcement of the frequency modulation method of transmission, attributed to the fertile brain of Frank Conrad and associates. For years the public has been kidded into believing that this and that development was revolutionary. But this discovery so far transcends in importance anything described in the last 12 years, it requires the use of superlatives which has heretofore been overworked. This time we find a real revolutionary discovery. Here is what frequency modulation (as compared to power modulation means : Return of the faithful regenerative sets. Elimination of local station interference. Greater signal at distant receiver. Partial solution of the fading problem. Extinction of the crystal set. Sixty per cent power saving at transmitter. More stations per channel. Hastens crystal control of all stations. Reduction of static-to-signal ratio. New field for receiver design. In the new modulation system instead of varying the amplitude of the signal component of the wave, this signal component is kept constant while the transmitting frequency is varied but not to exceed 500 cycles each side of the carrier straight line. Reference to the chart in this article will give an idea of the new scheme. The carrier frequency is shown as a beginning straight line. The frequency of the voice or music component is determined by the distance between the humps. The closer these humps lie the higher the frequency of the voice or music. The By F. A. HILL (Associate Editor) greater the distance between the humps, the lower the frequency of sound impressed. Since the frequency variation is not more than 1,000 cycles overall, it is easy to see how sharpened this form of transmission is. With the station's emission occupying but a thousand cycle band it will permit the presence of more stations within a given band without interference. Where in preseht modulation forms it is possible to receive broadcast music (although garbled) on zero beat with a regenerative receiver, under the new form of transmission music may not be received at zero beat. The only points at which music may be heard will be either side of zero beat. Zero beat will REALLY BE ZERO BEAT for nothing will be heard in that region. Local station interference will be abolished on account of the sharpened transmission and the necessity for a receiver with a much sharper frequency response curve. In the sketch with this article is also shown a graph of the signal intensity against distance. In the full line is the present modulation system where maximum signal is received at the point closest to the station, this energy dwindling off as the distance increases. In the new frequency modulation (dashed line) the signal intensity is at zero at the station and increases with the distance, up to a certain point, and then drops off as the distance increases beyond the range of the station. (Receivers set up in the station at KDKA will not pick up that station. The monitor set has to be located a mile or more away and the signal brought back over a telephone line so that station operators may listen to it). Experiments have shown that the signal under the new form is greater at a distance with the same, or less, power than under the old method of modulation. Due to an increased sharpness of transmission and a sharper receiver it has been noted that fading is considerably reduced. Likewise in this connection the static-to-signal-ratio has been cut. Crystal sets on account of their response curve will not pick up this form of transmission. (Continued on page 35) >' V t-r \ tn \ z ^v UJ N. ■z. \. -i ^^^^ < -z. „----~ ^^*^-^>^ ~~~~-~ <3 '"" -— -. "" ~~ (D ~~~~"---. DISTANCE . 100 CYCLES 5000.CYCLES t r~\ l r~\ 1 500 CYCLES — "CARRIER \ J T 500 CYCLES L_ [carrier iiii 1 ■\ \^_j LJ ^ — /