Patent GB-599549-A (GB)
Title: Improvements in high-frequency radio relay stations
IPC: H04B7/165
Filed: 1944-09-22
Abstract: 599,549. Radio-signalling; generating high-frequency oscillations; frequency modulation. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Sept. 22, 1944, No. 18179. Convention date, June 16, 1942. [Class 40 (v)] A radio relay station for angular-velocity modulated waves comprises a plurality of frequency-changing stages for producing from the received waves other modulated waves of a mean frequency bearing a constant relationship to that of the received waves, at least one of the frequency-changing stages being a heterodyne stage for mixing received modulated waves whose mean frequency has been reduced in preceding stages with frequency-divided received waves of a low frequency. The constant frequency relationship may be achieved by using a local oscillator for two heterodyning stages where the frequency changes are achieved in opposite senses so that drift of the local oscillator has no effect on the re-radiated mean frequency. Alternatively, the local oscillator may be dispensed with, the inputs to the heterodyning stage or stages being derived by frequency division only. As shown, Fig. 1, angular velocity modulated waves received on antenna 2, at a mean frequency of e.g. 500 mc /s. are amplified at 6. A portion of the output therefrom is frequency divided and amplified at 10 to give an output at e.g..5 mc/s. which is further amplified and filtered at 14 and fed to a frequency changer 26. Another portion of the output of amplifier 6 is heterodyned at 16 with e.g. a 600 mc /s. wave derived from a local oscillator 20 and frequency multiplier 22. The difference frequency of 100 mc/s. is selected by a filter and amplifier 24 and heterodyned at 26 with the .5 mc/s. output from amplifier 14. The sum frequency, 100.5 mc/s. is selected by amplifier and filter 30, heterodyned at 32 with the 600 mc /s. output from the local source 20, 22 and the difference frequency, 499.5 mc/s., selected by the filter and amplifier 38 is radiated from antenna 42. Since the output of the local oscillator 20 and frequency multiplier 22 is used in the two heterodyning units 16, 32 in which the frequency changes are effected in opposite senses, frequency drift of the local oscillator 20 has no effect on the resultant reradiated output. The modulation frequency swing of the received wave assumed to be 200,000 c/s. is divided by 1000 in the divider 10. The reduced frequency swing of 200 c/s. present in the output of filter 14 reacts in the frequency changer 26 to modify the modulation of the output from filter 24 and hence the re-radiated wave from antenna 42, but its effect is insignificant. The frequency divider 10 may, alternatively, be fed from the output of amplifier 38 with suitable division. The frequency dividers may be such as described in Specification 562,993. In a modification, Fig. 2, the wave received on antenna 200 at e.g. 1000 mc/s. is amplified at 204, frequency divided at 208 to produce a 1 mc/s. wave, at 218 to produce a 500 mc/s. wave and at 220 to produce a 0.1 mc/s. wave. In converter 212 the outputs of converters 208, 220 are combined, the sum (or difference) frequency of 1.1 mc/s. being selected and combined in a converter 224 with the 500 mc/s. output from divider 218. The sum (or difference) frequency of 501.1 mc/s. is selected, amplified and frequency multiplied at 230, amplified at 232 and re-radiated at 234 at e.g. 1002.2 mc/s. The modulation frequency swing of the reradiated wave is substantially the same as that of the received wave, the modifying effect of the frequency swing of the output from divider 220 in the converter 212 being negligible. In a further modification, Fig. 3 (not shown), two different sub-multiples of the received wave, both obtained by frequency division, are heterodyned, the sum or difference frequency being selected and re-radiated direct or after. suitable frequency multiplication. In the arrangements of Figs. 2, 3, no local oscillator is used and the output frequency of necessity bears a fixed relation to the input frequency. In another arrangement, Fig. 4, the wave received at 800 is re-radiated at 818 at the same mean frequency, but with reduced frequency swing. The input wave at 1000.5 mc/s. is heterodyned at 804 with a 999 mc/s. wave derived from a local oscillator, the difference frequency of 1.5 mc/s. being selected and amplified at 808, frequency divided by two at 810, amplified at 1000, and mixed at 902 with a .5.00025 mc/s. wave derived by frequency division of the received wave at 1002. The sum frequency of 1.25025 mc/s. is selected at 904, mixed at 812 with the local oscillator frequency of 999 mc/s. and the sum frequency of 1000.25025 mc/s. reradiated at 818 after selection and amplification at 814, 816. The Specification as open to inspection under Sect. 91 also contains the following subjectmatter. In Fig. 4 (Cancelled), the wave received on antenna 500 at e.g. 600 mc/s. is heterodyned at 502 with a wave of 599 mc/s. derived from a local oscillator 504. The difference frequency is selected and amplified at 506, multiplied at 508 to e.g. 3 me/s., and heterodyned in converter 510 with the 599 mc/s. wave from oscillator 504. The sum (or difference) frequency is selected by filter 512 and radiated at 516 after amplification and, if desired, frequency multiplication at 514. In a further modification, Fig. 5 (Cancelled), the received wave at e.g. 600 mc/s. is heterodyned in a converter 602 with e.g. a 601 mc/s. wave from a local oscillator 604. The difference frequency is selected, amplified at 606, frequency multiplied to e.g. 4 mc/s. at 608, amplified at 610, and heterodyned at 612 with the 601 mc/s. wave from oscillator 604 and filter 620. The difference (or sum) frequency, 597 mc/s. is filtered at 614, amplified at 616 and radi.ted at 618. In this embodiment, the modulation frequency swing of the received wave is multiplied in the frequency multiplier 608 resulting in a correspondingly multiplied frequency swing in the radiated output. If it is desired to re-radiate with the same modulation frequency-swing, a portion of the output of the amplifier 606 is fed to a discriminator and signal demodulator 624, e.g. as described in U.S.A. Specification 2,121,103. The demodulated signal may then be fed to a reactance tube modulator 628 to modulate the local oscillator 604 in such a sense as to reduce the frequency swing in the output of amplifier 606 and hence in the radiated output. Alternatively, by suitable choice of time constants in the unit 624, the units 624, 628 may be used for A.F.C. of the oscillator 604 without reducing the modulation frequency swing. The discriminator 624 may, alternatively, be coupled to the output of amplifier 616. In another modification, Fig. 6 (Cancelled and not shown), the frequency multiplier 508 of Fig. 4 (Cancelled) is replaced by a frequency divided so that the re-radiated wave is at a reducer frequency and a smaller modulation frequency swing. The received wave may, alternatively, be re-radiated with reduced frequency swing, but at the same mean frequency, Fig. 7 (Cancelled and not shown), by heterodyning the output of the frequency divider 508 back to the mean frequency of the output of I.F. amplifier 506 by a further local oscillator. This heterodyned I.F. would then 'be combined with the waves from oscillator 504 in converter 510. Specification 544,502 is referred to. This subject-matter does not appear in the Specification as accepted.