JPS63148731A - Fm transmission method - Google Patents

Abstract

PURPOSE:To improve C/N in a receiving side by multiplying an FM modulated wave, widening a frequency deviation and sending it out, returning it to its original frequency deviation in the receiving side and demodulating it. CONSTITUTION:An FM modulated wave alpha is multiplied by an multiplying circuit 1 and a frequency deviation is widened by the share of multiplied number and sent out to a transmission line 2, and in a receiving side, noise is eliminated by a limiter 3, etc., and thereafter, it is returned to its original frequency deviation by a frequency divider 4 with a frequency dividing ratio of a share multiplied in a transmitting side, and demodulated by a general demodulator. In this regard, if a demodulator of the receiving side can demodulate of the FM demodulated wave of a wide frequency deviation, it is also possible to demodulate without dividing a frequency by the frequency divider 4.

Description

Detailed Description of the Invention (Industrial Field of Application) The FM transmission method of the present invention includes, for example, optically multiplexing and transmitting FM-modulated television audio signals through an optical fiber cable.
It is used when transmitting via CATV coaxial cable or sending out as on-air waves.

(Prior art) When transmitting an FM modulated signal such as a television audio signal by optical multiplexing using an optical fiber cable or transmitting it using a CATV coaxial cable, it is possible to transmit it over as long a distance as possible with the S/N ratio. It is hoped that the results will be good. For this purpose, the C/N (carrier-to-noise ratio) on the sending side must be good.

(Problems with the Prior Art) In the conventional FM transmission method, the FM modulated signal is sent out as it is, so there are the following problems.

(1) In order to improve the S/N ratio, it may be possible to transmit the FM modulation signal (for example, a television audio signal) using a separate carrier, but if this is done, the wave number of the signal increases, making distortion more likely to occur.

(2) In order to improve the C/N, it is possible to increase the carrier wave transmission level, but in optical multiplex transmission systems, CATV systems, etc., the maximum output level of the amplifier is fixed, so increasing the carrier wave level will cause distortion. , the C/N decreases, and as a result, the S/N on the receiving side deteriorates. Therefore, there is a limit to how high the carrier wave level can be raised.

(3) In order to solve the problem like (2) above, it is possible to lower the carrier wave level, but if the carrier wave level is transmitted at a low level, the C/N on the receiving side will decrease, and the S/N will deteriorate when demodulated. do.

(4) If the frequency deviation is large, the S/N will be the same even with the same C/N.
Conventionally, it has been considered to demodulate the modulated wave once and then re-modulate the frequency shift to a wide range before transmitting it. However, doing so would complicate the demodulation and modulation circuitry, and the demodulation circuit on the receiving side would not necessarily be able to demodulate FM waves with a wide frequency deviation, so even if the frequency deviation is widened, it will not be effective. Sometimes there isn't.

(Objective of the Invention) The object of the present invention is to transmit a once-modulated FM wave at a low level, such as an FM broadcast wave or a TV broadcast audio signal, and to widen the frequency deviation with a simple configuration. Ensure a fairly high S/N when demodulating on the receiving side,
Furthermore, it is an object of the present invention to provide an FM transmission method that can be demodulated even by a general receiver.

(Means for Solving the Problems) The FM transmission system of the present invention multiplies the once modulated FM wave on the sending side, widens the frequency deviation by the multiplication number, and sends it out.
On the receiving side, the frequency shift is maintained as it is, or the frequency is divided by a multiplication number to return to the original frequency shift, and then demodulated.

(Operation of the Invention) The present invention multiplies the FM modulated wave (α in the figure) by a multiplier circuit 1, widens the frequency deviation by the multiplication number, and sends it out to the transmission line 2.

After noise is removed by a limiter 3 on the receiving side, the signal is returned to the original frequency deviation using a frequency divider 4 having a frequency division ratio of the multiplied frequency on the sending side, and demodulated using a general demodulator.

Note that if the demodulator on the receiving side is capable of demodulating FM modulated waves with a wide frequency shift, the demodulation may be performed without frequency division using the frequency divider 4.

(Effects of the Invention) The FM transmission method of the present invention has the following effects (1) A high S/N is ensured on the receiving side.

(2) It becomes a transmission system with a simple configuration.

(3) S/N does not deteriorate even through a transmission path with a low C/N.

(4) An FM transmission method that can be demodulated even with a general receiver.

[Brief explanation of the drawing]

The figure is an explanatory diagram showing one embodiment of the present invention. l is a multiplier circuit 2 is the transmission line 3 is limiter

Claims (1)

[Claims] The modulated FM wave is multiplied on the transmitting side to widen the frequency deviation by the multiplication number, and the receiving side returns to the original frequency deviation with the same frequency deviation or by dividing the frequency by the multiplication number. An FM transmission method characterized by demodulating.