Patent GB-656188-A (GB)
Title: Improvements in arrangements for locating defective submerged repeaters
Inventor: ROE FREDERICK ORMESHER
IPC: H04B17/40
Filed: 1948-02-17
Abstract: 656,188. Unattended repeaters. STANDARD TELEPHONES & CABLES, Ltd. Feb. 17, 1948, No. 4615. [Class 40 (iv)] In an arrangement for testing unattended repeaters in a carrier current communication system and for identifying a faulty repeater, a terminal station transmits a current of characteristic frequency corresponding to a given repeater which has means for producing a response current on receipt of its corresponding frequency. In the embodiment shown in Fig. 1, two terminal stations 1, 2 are connected by a twoway multi-channel circuit 3 including a number of repeaters such as 4, 5, 6 and 7, of which 6 is shown in more detail. Station 1 transmits on 12 to 60 kc/s. per sec. and station 2 on 72 to 120 kc/s. per sec., the usual transmitting and receiving equipment (not shown) being connected to conductors 8 and 9 respectively at station 1 and similarly at station 2. At station 1 band-pass filters 11, 12 and 15 are designed to pass bands from 12 to 61 kc/s. per sec., from 72 to 122 kc/s. per sec. and from 120 to 122 kc/s. per sec. respectively. An oscillator 14 supplies any one of a series of frequencies between 60 and 61 kc/s. per sec., a different one of which is allotted to each of the repeaters. Each repeater is provided with a harmonic generator 24, shown in detail in Fig. 2, which accepts only the particular frequency allotted to the repeater and generates its second harmonic in a rectifier 27 or similar device. A resonant circuit 29, 30 is roughly tuned to this second harmonic and an attenuating pad 28 is also provided. The second harmonic lies in the range 120 to 122 kc/s. per sec. and is therefore transmitted back to station 1 where it is selected by the band-pass filter 15 and measured by a transmission measuring set 16. In testing, the oscillator 14 transmits in turn the frequencies allotted to successive repeaters until an abnormal response indicates that the corresponding repeater is defective. In a modification, testing is carried out from the station transmitting in the upper band and the device 24 is then a frequency divider of suitable type. In a second testing arrangement, provision is made for following the deterioration of the valves in any repeater. The oscillator 14 supplies a set of frequencies in the lower band, preferably certain of the carrier frequencies, while an oscillator 33 at station 2 is arranged to supply a set of frequencies, preferably carrier frequencies, in the upper band. One of each of these sets of frequencies is allotted to each repeater, the difference between the two allotted frequencies being the same for each repeater and lying in the lower band. This common difference must not be one of the allotted frequencies. The low-pass filter 23 of the repeater 6 is modified to eliminate the lower allotted frequency and the high-pass filter 20 is made to eliminate the higher allotted frequency. Then both allotted frequencies will reach the amplifier 17 but will proceed no further, so that no other repeater will receive both the frequencies allotted to the repeater 6. Similar modifications are made in the other repeaters. The two allotted frequencies are transmitted at such a level that the amplifier 17 is operated at about the overload point, so that intermodulation will occur to produce the difference frequency which is transmitted to station 2 and measured by a transmission measuring set 32. As the valves in the amplifier 17 deteriorate the amount of intermodulation, and hence the strength of the difference frequency current, will increase, thus enabling the deterioration in the valves to be followed. Specification 446,225 is referred to.