Alarmempfänger 45 (Air Attack Alarm Receiver 45), E45; developed and produced by Autophon AG, Solothurn.
The E45 has been used as an Air attack Alarm receiver by the Swiss Airforce and Anti-Aircraft troops. A special transmitter transmitted tone coded signals to switch the receiver loud from standby operation when when an air attack message was transmitted.
There has been a possibility to switch the receiver to one out of five „Alarm Groups“ with different tone coding, so only receivers in a certain area could be addressed. This feature has been eliminated during a modification of the E-45 receivers on later years, when this set has been only as simple surveillance receiver.
There has been the possibility to control the receiver frequency from crystals stored in a compartment of the power supply case.
The receiving equipment consists of the Receiver E45 in one case / container and EZ45 in a second case, this one containing a separate mains power supply and an integrated audio stage with volume control (with a EBL-21 AF tube) and speaker. Both sets are connected by a heavy multipole cable.
The front panel is divided in two sections by the horizontal linear dial of the turret tuning arrangement. Above the dial, you find from the left hand the coaxial antenna connector and the sockets for connecting longwire antenna and earth, the crystal socket and switch for fixed frequency operating using speciyl crystals, then the clock (many of these neat Swiss clocks have been taken away by station personnel when these receivers have been taken out of duty), and the signal strength meter. At the right upper corner, you find the switch for the Alarm groups (tone coded) and the socket for the multipole cable (caution: the receiver is almost useless without this cable) and some fuses.
Underneath the frequency dial, You find the rotary band switch operating the turret tuner - find the corresponding dial in the dial window - and at the right hand the main tuning knob with a mechanical blocking arrangement. Two pushbuttons allow to switch the receiver „loud“ manually and to reset to muted „Alarm surveillance mode“.
On the image, you find the more rare variant E45Z / EZ of the power supply / AF stage with an internal speaker and speaker volume control and a second volume control for field telephone connectors. This variant of the E-45Z has been used in command posts.
Many thanks to Daniel Jenni, who sold this set in mint condition to me.
The antenna signal has to pass two RF preamplifier stages (D1F); it is converted to an IF of 1600 kHz in the mixer stage (D1F). This is followed by two IF amplifier stages (D1F, D1F). Then, the signal is demodulated (D1F and fed to the audio preamplifier (D1F), it's output is sufficient for headphones operation. The audio final stage with two DLL21 in a push - pull arrangement and the speaker are located in the power supply cabinet.
THe „Alarm Section“, which acted as a selective call unit, with it's four D1F valves was removed from the receivers according to a technical direction from Feb. 1974.
From the Airforce and Anti - Aircraft Units, 87 receivers E45 have been ordered. The selective call unit has been removed in 1974, after this year the receiver was still used to monitor air raid alarm messages, but as it provided no squelch operation, very often, the volume was turned down and the messages ended unheard.