IE44266B1 - Improvements in or relating to broadcast radio relay transmission links - Google Patents

Description

The invention relates to broadcast radio relay transmission links with a pilot control device or receivers for use with such devices, where a plurality of channels, frequency-staggered in accordance with a given pattern are relayed together, for example a plurality Of television channels and a channel that may include the VHF sound broadcasts as a composite signal in one channel.

A radio relay transmission system of this type is described in the publication Microwaves January 1972, page 38, where channel converters are power converters whioh are supplied with the requisite carrier power in sufficient magnitude via a distributor network from a klystron oscillator. In this way, it is poss15 ible to provide that the items of channel information converted into the radio frequency level, having been combined in the channel filter circuit, are directly irradiated via antennae, it being possible to dispense with a wide-band transmitting amplifier designed fox the entire transmission band. - Travelling wave tube amplifiers suitable for this purpose must be designed taking into account impermissible cross-modulation products for a high saturation power, and therefore involve a relatively high technical outlay in cost and labour. - 3 To ensure a satisfactory operation of such a radio relay transmission link it is necessary to take numerous measures at the transmitting station in order to suppress any cross-talk due to undesired couplings within those parts of the distributor network at which the signals have a high power level, especially for the supply of the carrier oscillation to the channel converters.

Also a disadvantage of the known system is that the pilot signal which is additionally transmitted for control purposes from the transmitting station to the receiving station is determined in its frequency by the frequency of the fundamental oscillator used in the transmitting station for producing the respective carriers. With regard to selective fading on the transmission link it is in fact effective to arrange the frequency of the pilot oscillation approximately in the centre of the overall transmission band, which itself contains all the channels. However, this presupposes in practice a free selection of the frequency of the pilot signal, since the centre position of the information band which under given circumstances will be transmitted in such a system can vary within a wide frequency range.

One object of the present invention is to provide a construction of a broadcast radio relay transmission device which, in particular in respect of a distributor network of the carrier supply for the various channel converters, requires only a minimal outlay in decoupling measures and filter means, and in addition permits a free selection of the frequency of the pilot signal required for the operation. 4426® - 4 The invention consists in a broadcast radio relay transmission link of the type providing pilot control for a plurality of channels frequency-staggered in accordance with a given pattern, in which a transmitting station is provided with a number of channel converter units corresponding to the number of channels, each with a respective amplifier connected between an associated signal input and a respective, filter feeding an associated signal output, a common carrier supply being provided for all the channel converter units, and a channel filter circuit being provided which combines all the channel information for feeding to a common output, means being provided at a receiver station to reconvert the incoming items of channel information into their original, respective transmitting frequency bands in accordance with said frequency-staggered pattern, the carrier supply for all the transmitting station channel converter units being in the form of a crystal-controlled oscillator of high frequency constancy stability with following frequency multiplication for each channel, said crystal-controlled oscillator for the transmitting carrier supply having a low output power level, and the requisite frequency multiplication of its output oscillations for each channel converter unit being effected by respective frequency multipliers of substantially mutually identical design prior to production, of respective high power carrier signal oscillations.

The invention is based on the recognition that the distributor network for the carrier supply can be of extremely simple construction if the actual frequency multiplication is carried out with a low output power level from the crystal-controlled oscillator, and in each case multiplication is only effected close to the location of a channel converter stage. The reason for this is that the danger of an electromagnetic coupling or cross-talk coupling between electric circuit components is less, the lower the power level of the high-frequency signal conducted in such a line network, and the lower its frequency.

The crystal-controlled oscillators, which exhibit a sufficiently high frequency stability at the transmitting and receiving stations for reliable carrier supply allow a mutual compulsory synchronisation to be dispensed with, so that the pilot which is additionally transmitted to the receiving station for control purposes no longer needs to be fixed in respect of its frequency. Therefore, it is advantageous for the pilot signal, which is separated from the incoming items of channel information at the receiving station, to be provided exclusively for purposes of level control.

In a preferred embodiment of the invention, for each transmitting station channel, a semi-conductor amplifier, preferably a semi-conductor power amplifier, is provided between the output of the respective frequency multiplier hnd the carrier input of a converter stage having a signal input for the respective channel information. The frequency multiplier itself only requires to be designed for a low power, as the actual amplification of the carrier oscillation is not carried out until after this multiplier. Therefore the multiplier can be of simple and inexpensive design.

The semiconductor amplifier can be realised in various ways. In a first preferred embodiment it is a semiconductor oscillator, preferably an Impatt-diode oscillator which is frequency synchronised by the respec5 tive oscillation from the frequency multiplier fed by the crystal-controlled oscillator . Instead of frequency synchronisation, it is also possible to employ a phase synchronisation, if the semiconductor amplifier is in the form of a semiconductor oscillator whose phase is controlled by a phase control circuit using the frequency multiplied output of the crystal-controlled oscillator.

For many applications it is conceivable to provide a respective semiconductor amplifier supplying a frequency multiplied carrier oscillation to an input of the converter stage of its channel at a relatively low power in the order of 100 mW, and to provide a common semiconductor amplifier operating with field effect transistors at the output of the channel filter circuit. In this case each individual channel semiconductor amplifier only requires to be designed for a relatively low power amplification, in the order of a few dB, so that any undesired intermodulation products which thus occur are kept within negligibly small limits.

Expediently the transmitting-end channel filter circuit possesses a number of circulators which corresponds to the number of channel converters, said circulators being interconnected to form two chains. The two chains are combined at their signal-sum-outputs via a summing element, preferably a directional coupler, and the various items of channel information are distributed amongst the corresponding inputs of the - 7 circulators in such manner that the mutual frequency spacing of two items of channel information relative to two successive circulators in a circulator chain is as large as possible.

In the practical use of a radio relay transmission link of the type in question, the number of items of television channel information to be transmitted, together with the VHF band will fluctuate, for example within limits from 3 to 16 channels. For this reason it is effective to design at least the transmitting station of such a radio relay link in such manner that it can be increased or reduced in size in respect of the number of channel converters required without difficulties. In this connection it is advantageous to combine each of the transmitting station channel converter units with its respective circulator provided for linking in the radio frequency level.

The invention will now be described with reference to the drawings, in which:Figure 1 graphically illustrates a channel allocation pattern including the VHF and UHF television bands and the VHF sound band UKW; Figure 2 is a block schematic circuit diagram of one exemplary embodiment of a transmitting station of a radio relay link constructed in accordance with the invention; Figure 3 schematically illustrates details of one exemplary channel filter circuit constructed with circulators, together with the antenna output circuit of the Figure 2 embodiment; 4 2 6 6 Figure 4 illustrates further details of a channel converter unit for use in an embodiment in accordance with the invention; Figure 5 shows a variant of the circuit shown in Figure 3; Figure 6 illustrates a variant of the semiconductor amplifier of the channel converter unit shown in Figure 4; and Figure 7 is a block schematic circuit diagram of a receiving station of a radio relay transmission link constructed in accordance with the invention.

The graph illustrated in Figure 1 shows the frequency allocation pattern covering a frequency band of approximately 300 MHz for a total of 30 television signal channels together with a channel of similar band-width for the VHF sound broadcasting band UKW, in the range between 87.5 and 105 MHz. In order to achieve an economical outlay in filter means, the transmission of items of television channel information including the UKW band via a radio relay distributor or feeder system can comprise a maximum of 15 items of television channel information, two in the VHF band, together with the VHF sound broadcasting on a single channel UKW. The mutual frequency spacing of the carrier frequencies then amounts to at least 14 MHz.

In the frequency allocation pattern shown in Figure 1, this is expressed by showing two television channels to be transmitted consecutively in the VHF portion of this raster indicated as shaped sections and separated by an unfilled television channel. _ 9 _ 44266 In this case the channels used in the UHF band are the thirteen unshaded sections, but it will be readily apparent that shaded channels could be used for television channel information. When the frequency allocation pattern has to accommodate less than 15 items of television channel information, mutually adjacent shaded and unshaded zones can be used together, maintaining the requisite spacings.

The block schematic circuit diagram shown in Figure 2 illustrates the transmitting station of a radio relay transmission link constructed in accordance with the invention, designed for a maximum of 16 items of channel information, 15 television channels and the UKW sound broadcast band which are made available at source outputs sl to sl6 for the television channels and the sound channels UKW, which latter are combined at one output of a source unit Q-TV. Each of the terminals sl to sl6 is connected to the signal input of an identical channel converter unit, but in Figure 2 only the channel converter unit Ul is illustrated in detail. Each channel converter unit possesses an amplifier Vs. at its signal input, which feeds a signal input of a converter stage U whose output signal is connected via a band-pass filter BP to the associated input terminal Sl to S16 of a channel filter circuit ZS. A common carrier supply is provided by a crystal-controlled oscillator KO of high frequency stability, the output of the oscillator KO being fed via a distributor network to associate input terminals £1 to ul6 of the channel converter units to produce the required carrier oscillations. As illustrated for the channel converter unit Ul, the output oscillation 442Θ6 of the oscillator is fed via the input ul to a frequency multiplier FV, which has a multiplication factor n, and having been multiplied, is amplified in a semiconductor amplifier VO before being passed to the carrier input of the converter stage U. A pilot signal required for control purposes at the receiving station is prepared in an assembly UP having an output SP for the radio frequency level, and an input up connected to the oscillator KO, the assembly UP forming a further converter unit which in its fundamental construction differs from the channel converter units merely in that a pilot generator Pi is provided in place of a signal-input amplifier Vs. The channel filter circuit ZS combines the items of channel information which are supplied by the channel converter units and have been converted into the appropriate radio transmission frequency, including the composite UKW band, to form a common radio frequency band transmission vzhich it emits via antennae Al and/or A2. Emission via only one antenna is possible. If two antenna outputs are arranged on the output side of the channel filter circuit, an antenna output which is not in use must be provided with a terminal impedance.

Two or even more antennae may be used, in particular whenever directional transmission in different directions is to be effected.

The channel filter circuit ZS can be constructed in various ways. The exemplary embodiment shown in Figure 3 represents a particularly favourable realisation in respect of low attenuation losses because of the use of circulators. As can be seen from Figure 3, the channel information signals converted into the appropriate radio frequency level, including the composite sound-channel UKW band, are initially coinbined in subbands via respective circulators Zl to Zl6. The combining is effected in that each of the circulators Zi (where i_ is an odd number in one case or an even number in the other) form separate circulator chains whose sum signal outputs are combined via a directional coupler RK, and the overall signal is transmitted via antennae Al and A2 with equal power in this embodiment. Here it is assumed that the index numbers i. of the circulators agree with the index numbers of the terminals si to sl6 of the sources Q-TV, and in addition that these index numbers reflect the frequency position allocation of the items of television channel information, together with the channel including the UKW sound band, in rising sequence in accordance with the frequency allocation pattern illustrated in Figure 1. In this way it is ensured that the mutual frequency spacing of two items of television channel information which arise at the corresponding inputs of two consecutive circulators of a chain, amounts to 28 MHz. With this frequency spacing it is possible to achieve the requisite backwards attenuation of >30 dB for a circulator without the need to make special demands on the production or technical design of the circulators.

As a rule, in a radio relay transmission link such as that on which the invention is based, the requisite transmission capacity requirement will fluctuate, in dependence upon the case of use, between 3 and 16 channels. In order to be able to make possible later extensions in a simple fashion, expediently a unit such as that shown in Figure 4 is used for the channel converter unit Ui.

This unit includes the respective circulator Zi. of the channel filter circuit, which is required for combining the separate television information channels converted into their transmission frequency state for each channel converter unit as an integral feature.

As can also be seen from Figure 4, the amplifier VU can be designed in various ways, and in this case is an Impatt-oscillator I, which is synchronised by the IO oscillation applied via the multiplier, after being frequency multiplied by a factor n when supplied from the common oscillator KO, which represents a common carrier supply (Figure 2). An Impatt oscillator of this type facilitates an effective power amplification to provide an output level of a few Watts, with relatively simple means, at very high frequencies.

Figure 6 shows a variant of such an amplifier VU. The oscillator I', for example a Gunn oscillator, is phase synchronised by means of a phase control loop P by the oscillation from the common oscillator KO after this has been multiplied by the respective factor n.

As can be seen from the channel filter circuit ZS in Figure 3 the items of information which have been converted into the radio frequency position by the channel converter units Ui having been combined, may be transmitted via the antennae Al and A2 without further amplification. The transmitting energy which is required for a satisfactory operation across a radio link in the order of 30 km is obtained in the channel converter units Ui which are in the form of 4 2 6 6 - 13 power converter units, and in fact primarily via the carrier power which is contrived to be of a corresponding magnitude. This carrier power is produced in the respective amplifier Vu which is designed as a power amplifier. In the variant embodiment shown in Figure 5, a channel filter circuit ZS' has a common semiconductor output amplifier V, which operates with field effect transistors, arranged between the antenna A and the output of a summing element SU which combines the sum signal outputs of the two circulator chains. In this case, it is sufficient if each channel converter unit amplifier VU does not produce an output power of approximately 1.5 W, but merely a carrier power of a few 100 mW. The semiconductor amplifier V, which in this case is designed to provide a few dB amplification, then raises the sum signal to the requisite transmitting level. The input-coupling of the pilot signal converted into the radio frequency position via a coupling K which in the embodiment of Figure 3 is effected at the output end of the circulator Z16, but is provided at the input of the common semiconductor output amplifier V in the channel filter circuit ZS' shown in Figure 5.

The block schematic circuit diagram shown in Figure 7, for the receiving station of a radio relay transmission link exhibits a receiving filter EF following a receiving antenna EA. Subsequently each received frequency band is reconverted into its original level in a receiving converter unit EU whose output is amplified in a selective preliminary amplifier W and is then fed to a respective main amplifier HV which is controllable in respect of its amplification. -14 The main amplifier assembly has two outputs, of which the items of television channel information or of the UKW sound band are available, in their original frequency positions, for further use at an output a. A second output is connected to the input of a pilot receiver PE, which latter separates the pilot signal from the sum signal and in dependence upon its amplitude emits a control signal to the control input of the main amplifier HV. The common carrier supply possesses a crystal controlled oscillator KO of high frequency stability similar to that provided at the transmitter, and whose output oscillation of relatively low frequency is multiplied by the factor n in a frequency multiplier EV, and fed to the or each respective amplifier VU. The amplifier VU raises the associated carrier oscillation to the carrier power value required for the conversion.

The common oscillator KO, at the transmitting station or at the receiving station is expediently operated under a thermostatic control with the aid of ™6 which a long-term frequency constancy of 2.10 can be ensured. This accuracy is adequate for an independent carrier supply at both the transmitting and receiving stations. The crystal controlled oscillator of the transmitting or receiving station common carrier supply emits an oscillation in the range between 100 and a few 100 MHz, as a result of which, in combination with the low output level previously described conditions are provided which are favourable for the construction of the distributor network.

As has already been pointed out, the common independent transmitting and receiving carrier supply circuits provide the possibility of positioning the frequency of a pilot signal, which has been transposed into the operating frequency position, into the centre of a band gap in the middle range of the transmission band. In this way, it is also possible, with simple means, to effect a frequency shift at an intermediate station of the radio relay link, if the distance to be bridged necessitates such an intermediate station.

In addition a radio relay transmission link constructed in accordance with the invention provides the possibility that particularly with critical radio fields, two pilot signals can be transmitted, of which one is arranged in the region of the upper limit of the radio frequency band to be transmitted, and the other is arranged in the region of the lower limit of the radio frequency band to be transmitted. For the transmitting station shown in Figure 2, this means that a second pilot assembly UP must be provided.

At the receiving station it will probably be expedient in this case to provide two pilot receivers, from the output signals of which the control value for the main amplifier can then be obtained via an analysis circuit.

Claims (11)

1. CLAIMS;1. A broadcast radio relay transmission link of the type providing pilot control for a plurality of channels frequency-staggered in accordance with a given pattern, 5 in which a transmitting station is provided with a number of channel converter units corresponding to the number of channels, each with a respective amplifier connected between an associated signal input and a respective filter feeding an associated signal output, a common carrier 10 supply being provided for all the channel converter units, and a channel filter circuit being provided which combines all the channel information for feeding to a common output, means being provided at a receiver station to reconvert the incoming items of channel 15 information into their original, respective transmitting frequency bands in accordance with said frequencystaggered pattern, the carrier supply for all the transmitting station channel converter units being in the form of a crystal-controlled oscillator of high frequency 20 constancy stability with following frequency multiplication for each channel, said crystal-controlled oscillator for the transmitting carrier supply having a low output power level, and the requisite frequency multiplication of its output oscillations for each channel converter 25 unit being effected by respective frequency multipliers of substantially mutually identical design prior to production of respective high power carrier signal oscillations.

2. A radio relay transmission link as claimed 30 in claim 1, in which means are provided to separate the pilot signal from the incoming items of channel - 17 information at the receiving station to be used for purposes of level control.

3. A radio relay transmission link as claimed in Claim 1 or Claim 2 in which a separate semiconductor amplifier is provided for each transmitting channel, between the output of the respective frequency multiplier and the carrier input of a converter stage having a signal input for the respective channel information.

4. A radio relay transmission link as claimed in Claim 3, in which said semiconductor amplifier is in the form of a semiconductor oscillator supplying a higher power output signal to its associated converter stage.

5. A radio relay transmission link as claimed in Claim 4, in which said semiconductor oscillator is an Impatt diode oscillator which is synchronised by the frequency multiplier output oscillation.

6. A radio relay transmission link as claimed in Claim 3, in which said semiconductor amplifier is a semiconductor oscillator whose phase is controlled by means of a phase control circuit using the frequency multiplied output of the crystal-controlled oscillator.

7. A radio relay transmission link as claimed in any preceding Claim in which the channel filter circuit possesses a common semiconductor output amplifier which operates with field effect transistors.

8. A radio relay transmission link as claimed in any preceding Claim, in which the channel filter circuit at the transmitting station possesses a number of circulators which corresponds to the number of channel 4420® converters, which circulators are interconnected to form two chains, said two chains having their sum signal outputs linked via a summing element, and the various items of channel information being distributed among the 5 corresponding inputs of the circulators in such manner that the mutual frequency spacing between two items of channel information, relative to two consecutive circulators in a circulator chain, is as large as possible.

9. 10 9. A radio relay transmission link as claimed in Claim 7, in which said channel converter units at the transmitting station are each linked as a unit together with the respective circulators provided for the combination of the radio frequency level outputs. 15 10, A broadcast radio relay transmission link substantially as described with reference to Figure 2, or as modified by any one of Figures 3 to 6.

10.

11. A broadcast radio relay transmission receiver substantially as described with reference to Figure 7.