Inhaltsverzeichnis
P-723/m
Direction finding system P-723/m, Telefunken Telegon IV / PST638; manufactured by AEG Telefunken AG, Ulm & Berlin.
The transistorised Telegon IV direction finder based on the PST 638 receiver was purchased in the late 1960s as a mobile near-field direction finder. The system, which was installed in a Volkswagen bus, could be used very flexibly to localise illegal transmissions, among other things.
Technical data
- Principle]]: Visual direction finder Telefunken PST 638
- Frequency range: 0.25 - 30 MHz, optionally 9.8 - 570 kHz
- Sensitivity: AM (A3) 4 μV/m / selectivity - 3 dB: Hearing channel „narrow“ 0.45 kHz; „wide“ 3.4 kHz; DF channel 0.5 kHz
Power supply
- Mains operation: (110;) 220 V
- Batteries: 24 V vehicle electrical system
Dimensions
Accessories
- Ferrite DF antenna PR 638/1
- AP 638/1 Adjusting device
- Frequency indicator FA 990
- Panorama display unit PaG 724
- optional longwave adaptor LW 638/1
System material
The Telegon IV direction finding system from AEG - Telefunken, Ulm was designed for fixed and mobile operation on vehicles or ships and has a modular structure.
The core component is the receiver with an integrated bearing indicator using a round cathode ray tube, the SiG 638/2 is transistorised and equipped with a DP 10/14 cathode ray tube.
A rotary bearing dial is manually aligned with the maximum deflection on the display and the bearing can be read.
Push buttons are used to select the frequency range 250-510 kHz or one of the nine ranges from 0.55 - 30 MHz. The frequency is displayed on a horizontal frequency dial.
The FA 990/30 frequency indicator is a digital frequency display: the reception frequency is displayed with Nixie tubes in the range 10 kHz - 30 MHz with an accuracy of 1 Hz, the frequency accuracy on the analogue dial is only around 4.8 - 11.6 kHz / mm dial length in the short wave ranges.
For operation, the set is connected to the AC mains, the main switch is located at the top right. For normal operation, the BETR.KONTR. switch is switched off, for AM reception the bandwidth is set to WIDE, the BFO/A1 oscillator and „chopping“ are switched off, the loudspeaker is switched on, the volume is set to approx. position 3 and the RF control to approx. position 8 and the On/Off control is set to the centre position. The waveband can be selected using the row of pushbuttons, the tuning knob is located at the bottom right.
The CRT display on the left-hand side of the front panel is used to display the direction finding bearing; the FOCUS and BRIGHTNESS controls are set to maximum sharpness; the brightness is adjusted so that there is no glare in the vicinity of the light spot. Two small screws behind the cover allow the light point to be centred. The ILLUM.(ination) control is used to adjust the brightness of the illumination of the compass dial, the CURSOR control is used to rotate the bearing ruler with the parallel lines and to read the result on the outside of the compass scale when it coincides with the bearing ellipse. The SENSE button switches to reception from the auxiliary antenna for side determination. For normal signal monitoring, you can operate from the auxiliary antenna only, when the side determination button is pressed in, it can be rotated for 90° after being pressed and thus locked.
A crystal calibrator, which produces a calibration mark every 100 kHz, is provided for testing the device under the designation BETR.KONTR. For testing in the long-wave range, the 0.25-0.51 MHz range is selected and the set is tuned to the calibration mark at 400 kHz; the corresponding band dial is backlit. With the BFO (narrow bandwidth) activated, a heterodyne tone is audible and the lowest frequency or maximum deflection of the ellipse is tuned. The RF control is now used to set the gain so that the ellipse reaches the edge of the compass scale as close as possible; the setting is made using the step switch and the fine control on the inner knob og GAIN CONTROL.
Now use the AMPL and PHASE controls to adjust the ellipse until it is as narrow and sharp as possible; the angle on the compass scale should be 45 % +/- 2° or the number shown in the label at the top right. Press the SIDE/SENSE button to activate the side determination; a cross now appears instead of the ellipse.
To use the system on VLF / longwave ranges 9.8 - 575 kHz without a gap in the IF range, the longwave adaptor LW 638 is connected to the receiver.
With the optional built-in wideband output BPA 638/2, the IF signal can be fed to a panorama display: Using the PaG 724/525 a range of 20 - 100 kHz width can be monitored for radio activity.
A PR 638/1 ferrite antenna mounted on the vehicle roof with various groups of ferrite rods is used as a DF antenna, the entire antenna is protected under a bonnet made of glass fibre reinforced polyester (this was called „Emmental cheese“) and is wear-free, as it has no moving parts.
For example, the insulated luggage rack mounted on the vehicle could be used as an auxiliary antenna.
The system could be powered from 110 - 220 V mains or from 24 V DC from the vehicle battery during mobile operation.
Technical principle
Single conversion superhet; direction finder with north-south and east-west antennas for XY deflection and auxiliary antenna for side determination.
Tube assembly
The set is fully transistorised, only the display tube is a conventional DP10-14 CR tube.
Development
The Telegon IV direction finder was developed by Telefunken in the mid-sixties and was sold over the years with various improvements in different versions.
Use
In Switzerland, the systems were installed in a closed VW 1500 bus; the large round direction finding ferrite antenna was concealed under a tarpaulin over the luggage rack. The vehicles were also equipped with an SE-208 for communicating direction finding commands and results.
In 1967, six systems for MW / SW and a further four systems with the additional longwave adaptor were purchased, the vehicles for the latter were painted in civilian colours and the station personnel on duty was wearing civilian clothing.
The systems remained in use until 1985 and were liquidated in 1989.
