SU56467A1 - The way to combat fading radio transmission - Google Patents

Description

Among the various methods of dealing with malicious communications that are used in modern radio communication, the introduction of modulation into a signal emitted by a transmitter is very common. This method turns out to be very effective for selective fading and, despite a certain expansion of the emitted frequency spectrum, is becoming more and more applied to real radio installations. It is understood that this method can be applied only to wireless telegraph stations.

The invention described below permits the application of the principle to radiotelephone lines of communication.

The essence of the invention is as follows. The audio frequency spectrum necessary for transmitting a conversation (for example, 300-2700 Hz) is inverted with the help of a well-known balanced module torso 3 with the frequency spectrum of 2700-300 Hz, i.e. the frequency of 300 Hz is converted into 2700 Hz and in 3000 Hz. In this form, the audio frequency band is supplied to the modulator transmitter cascade, and the fixed cascade of the transmitter is supplied with a fixed frequency 3000 Hz of constant amplitude, operating continuously (i.e., even during conversation pauses). The transmitter cascade modulated by these frequencies is also balanced, as a result of which the carrier frequency / o from the transmitter is suppressed and does not fall into the antenna.

The frequency spectrum emitted by such a transmitter is depicted in FIG. 1. Written under FIG. 1 digits correspond to radiated frequencies. The numbers in parentheses (above the boundaries of the sidebands) indicate the initial, prior to inversion, values of sound frequencies. FIG. Figure 2 shows one of the possible transmitter circuits creating a similar spectrum. Here is the M microphone; I-frequency converter according to the balanced modulator scheme, which inverts the spectrum of sound frequencies around the frequency 300 Hz An audio frequency generator, feeds the converter I. This same frequency is supplied to the balanced modulator B. F is a filter that transmits conversational frequencies 300-2700 Hz; L - the assigning cascade of the transmitter, cascades of preliminary amplification and multiplications; B - KGASKADI powerful gains.

The effect of the scheme is clear from the previous description.

Transmitter radiation can be thought of as two identical radio telephone transmissions, each consisting of a carrier frequency and one sideband. At the same time (Fig. 1) the carrier / o-f-3000 Hz and the band from / o-2700 to / o + ZOO constitute one gear, and the carrier / o - 3000 and the band from / o - 2700 to / o -300 make up the second gear. Such a transmission is received at one time by two receivers operating from a common antenna (FIG. 3). Receiver Pr / is tuned to the first gear (with carrier frequency /, - f-3000) and with the help of the filter F it frees itself from the frequencies below. Receiver PrL is tuned to the second gear (with carrier frequency / o - 3000) and using the filter Φ, it is released from the frequencies of fluff. / o - 300. The use of quadratic detection when converting to an audio frequency caracks against distortion and the absence of a flicker. As it is easy to see, when receiving this radiation, there is no need for frequency inversion, since the boundaries of the sidebands facing the carrier frequencies (Fig. 1) correspond to low sound frequencies. The input circuits of the receivers are connected in parallel.

The system of two receivers must be equipped with a general auto-adjustment of the receiving power, switched on in such a way that a period of 1pc with a larger carrier amplitude, MiicToTij, is released. in the simplest case ((ig. 3), this can be accomplished by adding the constant components in the APC circuits and summing the received voltage as a negative bias to both receivers.

The advantages of the proposed method of combating fading, as compared with the usual one, are as follows.

1. Changes in the phase of the carrier frequency or phase of the frequency in the sidebands are not accompanied by distortions.

2. The selective fading of one of the carrier frequencies will be received at the expense of the second carrier.

3. With selective frequency fading in one of the sidebands, reception can be done at the expense of the same frequency in the other band.

4. Finally, in order to combat common fading, it is possible to use diversity antenna reception, using, in addition to the two, a third receiver, powered by a separately installed antenna.

The output circuits of all receivers are connected in parallel; The APC is still turned on so that the receiver, to which the carrier frequency amplitude is larger, receives the greatest gain.

In order to further combat selective fading, it is advisable to switch to the proposed h. The APC method. the essence of which is that in the middle of the sideband a constant amplitude frequency is turned on, which is emitted continuously. By a special filter, this frequency is suppressed in the main channel of the receiver, while another filter is allocated, then rectified, and in this form is used to adjust the gain of the receivers.

The subject matter of the invention.

The method of dealing with the fading of a radiotelephone transmission, especially on Short Loopes, is so dangerous because they radiate and attenuate sidebands and eliminate the carrier wave, and also apply a constant, constant amplitude to the modulator, and to receive this radiation, There are two receivers, each tuned to the carrier and one of the sidebands and connected in parallel with the output circuits. Copyright Certificate № 56467 M.P. Dolukhanova

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