STATION CONSTRUCTION SECTION.
In October 1942 the only SOE Station in the United Kingdom had its receiver site located at Grendon-Underwood and its transmitter site at Charndon. The Signal Office was in a down-stairs room in the house but a new building was under construction capable of accommodating equipment for increased traffic demands. The transmitter building whose dimensions were 20' by 12', housed eighteen 250 Watt transmitters. One 20-pair cable was installed between the receiver and transmitter site for remote control. Stand-by power supply was available from a 9 kVA P/E generator at both sites.

The problem which presented itself at this time was due to ever increasing traffic. Originally the station had been designed to cater for a smaller number of channels and at that time no doubt the space available was sufficient. Now, however, the transmitter building was very overcrowded and considerable loss of efficiency and flexibility were most apparent. The original aerial installation had catered for 12 cage-dipoles, but subsequent modifications had increased this number to approximately 20. This had been done without increasing the number of masts.


Initial steps taken to increase traffic handling capacity.


Receiver Site
.

The general lay-out of the Signal Office was considerably improved and there was a total of 18 operating positions of which 4 were equipped for automatic sending. A superintendant's desk was installed, where facilities existed for connecting any operating position to any transmitter and also allowed the superintendant to monitor any receiver.
The receiving aerials which consisted of 8 Rhombic and 4 cage-dipoles were not modified, but the feeder was diverted to the new building. These aerials were permanently connected to 12 of the receivers and the remaining 14 were connected to a new set of end-fed aerials erected round the Signal Office.
A new 28-pair remote control cable was now made available for service, although its main function was to be a stand-by nature. To achieve this satisfactorily this route to the transmitter site was different from the original 20-pair cable.


Transmitter site,

It had been decided that a second transmitter building was necessary to house further transmitters and a building measuring 35' by 18' had been erected. A further 6 250 Watt transmitters were installed here. Four half-wave dipoles were erected and arrangements were made so that any aerials could be connected to any transmitter. In addition each transmitter had available two end-fed aerials, one for day frequencies and one for night frequencies. Adjustments of length could be made electrically by matching units. The 28-pair remote control cable was extended to this building.



Construction of Station 53B.

The reconstruction outlined above was not sufficient to handle the increasing load and it was decided that an additional station was required. The receiver site chosen was at Poundon and that for the transmitter at Godington.


Receiver site
.

In the light of the past experience a very much larger scale Signal Office was build. This measured 40' by 12'. Here 40 operating positions were built of which more than half had sufficient space to permit installation of automatic sending facilities.
A new technique was employed in this Signal office in the use of Wide-Band amplifiers. these afforded great economy in aerials because each amplifier was capable of operating simultaneously as many as 50 receivers.
Two 3-wire receiving Rhombics were built, covering between them a frequency range of 3 - 13 MHz. In addition two single-wire Rhombics were built, each capable of operating 4 receivers simultaneously without the use of the Wide-Band amplifier.
The amplifiers themselves were mounted on racks; a lay-out was designed so that any receiver could be connected to any of the 3 Wide-Band amplifiers installed or to the single-wire Rhombics. Each receiver position was wired with coaxial cable and a total quantity of some 7000 ft of cable was used. 15.000 ft lead covered pair was used for wiring the keying, High Tension switching and monitoring circuits.
A superintendant's table was installed where facilities existed for any operating position to be connected to any transmitter and monitoring facilities were also available.
A disk recorder was installed, consisting of a double turntable recording unit and a double turn table play-back unit. The output of any receiver could be recorded. At a somewhat later date the automatic equipment was improved by the addition of an undulator which again could be connected to the output of any receiver.
Subsequent additions to the facilities of the station were made and included the building of two more 3-wire Rhombics and a folded dipole. The number of Wide-Band amplifiers was increased to 5 to accommodate the additional aerial facilities.
A 9kVA P/E generator was fitted for stand-by power and a system of automatic switching was installed so that in the event of a power failure the alternative power supply was first selected and if this too failed the stand-by generator was brought into action. Voltage regulators were also installed.


Transmitter site.

A transmitter building 100 ft long by 24 ft wide was designed with special facilities for bringing in open wire feeder route. Thirty four (
34) 250 Watt transmitters, together with their remote control apparatus were installed, the wiring of which necessitated the use of some 600 ft of lead covered pair cable. All transmitters were mounted on platforms, and facilities were made so that in the event of a failure, any transmitter could be removed and quickly replaced by one in a working condition.
Six 20 ft, one 80 ft and fifteen 100 ft masts were erected, so that there were 32 dipoles and 2 Rhombics. Some 10.000 ft of wire was used in their construction, and approximately 3000 spreaders were used in the down leads. Open-wire feeder routes were employed erected on approximately 100 Post office telegraph poles and employing some 75.000 ft of copper wire.
A 40 kVA D/E generator was installed for stand-by power. Automatic change-over in the event of power failure and automatic voltage regulation were fitted. Owing to the somewhat unusual requirements of SOE communications with the field, it is essential that transmitting stations should be capable of providing reasonable field strength over a wide area. Moreover, it is highly desirable that an operator should be able to change frequency on any transmitter with great speed. A standard 250 Watt transmitter requires on an average some four to five minutes to accomplish this accurately.
Investigations were made in order to meet these requirements and a Wide-Band transmitting amplifier working with three-wire Rhombic aerial was developed. Such an installation provided not only a good signal over a wide area, but would also transmit on twelve channels simultaneously, each channel giving a field strength  equal to that from a250 Watt transmitter connected to a resonant half-wave dipole.. Ant frequency between 3 MHz and 8 MHz could be transmitted on the first type of amplifier produced, but at a later date, a second model was brought into use, covering a range of 8 MHz to 13 MHz. The rapid frequency changing facility was most satisfactorily met: an average operator could do this in 30 seconds. One of the 3/8 MHz and one of the 8/13 MHz models were installed and were thus the first of their kind ever to operate in this country. Subsequently the total number of aerials in use was brought up to a total of 36 dipoles and 5 Rhombics.



Re-design and building of Station 53A.