The hollow state VHF aircraft radio SE-015 / STR.9-X, used in the fighter aircraft de Havilland "Vampire" und "Venom", is completely crystal controlled. A simple Control Unit is used to select one of ten pre-tuned operation frequency channels, the "Push-to-Talk" switch is also located at the control unit.

The aircraft radio has the characteristic modular construction: there is only space for a small control box in the cockpit of most fighter airplanes, the transceiver itself is located in an equipment bay usually located at the back of the aircraft. Several cables with multi-pole connectors (which are typically unavailable when searched for years later) connect the radio equipment with the on-board instalations of the plane.

After taking away the front cover, the crystal sockets can be accessed, they are suited to fit frequency crystals of the STC types 4004, 4044 and 4046 or the american equivalent HC/6U, the correct crystal frequency is (operation frequency divided by 18 - 0,54 MHz).
To tune the set, the transceiver has to be turned on with the control unit attached. The set has ten frequency channel slide strips for the ten pretuneable channels. After the slide releasing switch has been pulled outwards. For tuning the receiver section, the slide switch has to be pulled out for the first stop and the receiver tuning control is turned for maximum noise after the tuning control knurled locking disk is loosened. The the slide switch has to be pulled out for the maximum position to tune the transceiver section for maximum signal output, then the slide switch has to be set back in the middle position and the procedure is repeated for the next channel slide strip. After all pre-tuning is done, the knurled locking disks can be tightened and the channel strips are then moved electrically when the channel selector at the control unit is operated.

The transceiver is powered from the 26 V on-board power system of the aircraft, the heaters are powered directly, a rotary transformer is used to generate the plate voltage of 250 V and the grid voltage of 50 Volts.

A crystal controlled oscillator gives a signal between 5'848 - 7'515 kHz depending on the crystal in use, the operation frequency is generated by means of a frequency multiplier (two frequency tripler stages 3V1 and 3V2 and a frequency doubler stage 3V3). The operation frequency is the 18-fold of the crytsal frequency plus 9,72 MHz of the intermediate frequency.
I nthe receiver section, the antenna signal is moxed to generate an intermediate frequency of 9,72 MHz. This will have to pass three IF amplifier stages to be demodulated in a diode demodulator.
In transmit mode, the same oscillator signal after the first two frequency tripler stages is used, it will be mixed with a 4,86 MHz oscillator signal and will be fed to the modulator stages 4V2 / 4V3. After a frequency doubler stage 4V4 it is passed over to a RF dirver and final amplifier stage 4V5 and 4V6. The frequency of the emitted signal equals the 18 fold crystal frequency plus the double auxiliary oscillator frequency.
One example: with the 6,96 MHz channel crystal frequency, an oscillatorsignal of 62,64 MHz is generated after both frequency tripler stages 3V1 / 3V2, after beeing mixed with the auxiliary oscillator frequency of 4,86 MHz, a signal of 67,5 MHz is fed to the last frequency doubler stage 4V4, from which the final output on 135 MHz in the middle of the VHF air communications band will will result, this only needs further amplification to be transmitted.

The first four aircraft of the early DH-100 Mk 1 had the four channel STR 9 / SE-012 installed, the later DH-100 Mk 6 "Vampire" and DH-112 "Venom" came with the ten channel version STR.9X / SE-015. Later, the major part of the Swiss Air Force fleet has been equipped with this equipment, e.g. the C-3605, Pilatus P2, P3, PC-6, Do-27, Ju-52, Fieseler Storch and even the Hawker "Hunter". There also exists a 44 channel variant, the SE-015/1.

I would be very thankful for further information and images.