In the first six high power stations G1,5K - the "Big 1,5 KW Short Wave Stations" -
a Lorenz EO 509/I all wave receiver has been used as main receiver. In the later
stations with serial numbers above No. 15, the Lorenz "bread box" has been replaced
by the much more modern superhet receiver E41 from Zellweger, Uster.
The Lorenz EO 509/I is a regenerative TRF (tuned radio frequency) receiver,
it has two tuned HF circuits and four valves.
The twelve band segments of the EO 509/I can be switched by rotating a heavy
coil turret, the impressive coil arrangement can be seen, when the cover of
the receiver ist lifted off. It has only a logging frequency dial with the numbers
indicated in a small window at the right end of the cover, a frequency chart
on the receiver cover helps attributing the frequencies to the readings of the
A cariable capacitor "Korrektur" (stands for frequency "Correction") is used to bring
the two HF circuits in tune.
The signal from the antenna socket is amplified in a RF amplifier stage (MF 2) followed by the reaction
stage (Audion, operated by control "Rückkopplung" (regeneration)) (valve MF 2) for demodulation.
After two AF amplifier stages (valves MF 2, MF 2), the audio signal
is fed to the headphone sockets, the AF output power is not sufficient to drive a speaker.
For the reception of morse code transmissions (CW), the regeneration stage is brought into
oscillation (control "Rückkopplung") and the emerging howling noise makes the unmodulated morse code signals
A RF blocking circuit is provided to eliminate an interfering radio frequency signal
in the 1000 - 3750 kHz range, in addition to that, a selective 900 Hz AF filter ("Ton Selektion") can
be activated, this will only let pass morse code or Hell radioteletype signals.
Like most of the German marine receivers, this All Wave receiver is still
a regenerative TRF set on a very high standard - the German navy stepped back from
using superhet receivers on their ships for many years, because of a fear, that
their oscillator signal could be use to trace the ship's position. And like some
other German made marine receivers from the thirties, also the EO509/I comes
equipped with a crystal detector for emergence reception in case of a power
failure onboard the ship.
As the Lorenz EO509/I is still a regenerative set, it's sensitivity and
selectivity has been considered as quite poor compared to the reception quality
of the superhet receivers, a design which was preferred from American receiver
developers - even by the Swiss Army signalmen.
As this Lorenz receiver was considered as technically outdated, a poor performer
and without sufficient stability for Hell radioteletype operation by the Swiss Army,
it was replaced by the double conversion superhet E41 (All Wave Receiver Uster)
made by Zellweger, Uster, in the second badge of wireless stations G1,5K.