Aeronautical Ground Station SE-405
Z - Station / ZM - Station
Radio Corporation of America

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überarbeitet am 5.1.2013

The aeronautical ground station SE-405 consisting completely from RCA equipment is one of the few "real" aircraft traffic ground stations used by the Swiss Air Force, and not an adapted or impovised set.

The station consists of a powerful shortwave transmitter and receiver and two VHF frequency modulated transmitters and receivers.
The equipment was used for fixed operation in military airports or as relays in mountain station (designation Z-Station or SE-405/f) and for mobile operation on a Saurer 4x4 truck (ZM-Station or SE-405/m) and was acquired in 1948/50.

Shortwave transmitter AVTG 500R (RCA)

2 - 20 MHz ,

A1 (CW), A3 (AM)

pout A1, A3 500W

Shortwave receiver: RCA CR 91
(improved AR-88 for military use)

73 - 550 kHz, 1480 kHz - 30,5 MHz


VHF - Transmitter (2 samples)

105 - 156 MHz ,

A2 (telegraphy modulated), A3 (telephony AM)

pout A2, A3 225 W

VHF - Receiver: two AVRG-2R or E-505 / BC-624

100 - 162 MHz


When all aircraft communications were moved to the VHF frequency band in the late fourties, there was the demand to acquire completely new equipment for the aeronautical ground stations for the ground to air traffic. Additionally, "mountain stations" had to be established to make links between the airfields and fighter mission controls.
The RCA ground station purchased for this purpose consisted of shortwave and VHF equipment and got the designation SE-405 / Z-Station.

SE-405 Sender KW / VHF
The shortwave transmitter is a AVTG 500 R, a 500 Watts shortwave transmitter constructed by RCA, whoch can operate in CW telegraphy (A1) and telephony (A3). The shortwave band is covered in three ranges, all frequencies are crystal controlled.
In the 2 - 5 MHz frequency range, the crystal frequency equals the operation frequency, in the 5 - 13 MHz range, the operation frequency is the double crystal frequency and in the 13 - 20 MHz range, the crystal frequency is tripled. Different coil sets had to be used for the different band ranges. To match the antenna, a BC-939 A antenna tuner is used.
In the VHF air band, two transmitters with an output power of 225 Watts each are used, they cover 105 - 156 MHz. In a similar way, by plugging in shorting plugs, frequency doubler or multiplier stages are activated or bypassed. The transmitters can operate in telephony (A3, still in use today) and modulated telegraphy (A2) with an internal AF tone generator active.
SE-405 Empfänger RCA CR-91 SE-405 Empfänger RCA CR-91
The shortwave receiver of the Z-Station is a RCA CR-91, a variant of the classic RCA shortwave receiver RA-88LF with additional longwave coverage. The single conversion superhet with an IF of 455 kHz uses fourteen valves. The VHF receivers are two AVRG-2R, the RCA VHF receivers operate on a fixed frequency, both receivers are connected to one speaker unit.

For measurement purposes, a signal generator Boonton Modell 80 (to tune the VHF transmitters) and a kathode ray oscilloscope Dumont Modell 292 made part of the station equipment.

For shortwave transmission, a 70 Ohm dipole antenna or the vehicle whip antenna could be used, for VHF transmissions two fixed dipole antennas or the vehicle VHF dipole; for reception the shortwave main antenna or two auxiliary dipole antennas were used.

The station is powered from a three phase 250 / 380 / 500 V mains power supply or from a fuel operated generator PE-95 with 220 V / 60 Hz for mobile operation.

In 1948, eleven Z-Stations / SE-405 have been ordered, the mobile units ZM / SE-405/m served until 1969, the fixed stations SE-405/f were faded out in 1990.

further information:
The station is displayed at the Swiss Air Force museum at Dubendorf.
d: technical handbook of the Z-Station

© 5.1.2013 Martin Bösch