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This receiver was developed by the German manufacturer Wandel &
Golterman (W&G) in 1958 and was given the designator BN-58.
It was used with the SP-15 spy set
and later also with the SP-20 spy set.
W&G is widely known for the production of high-end electronic test
equipment such as audio and HF spectrum analyzers.
The BN-58 is also known as the FE-8 or as Empfänger SP-15
when part of the SP-15 radio station,
but also as SP-20E when it was part of the
SP-20 radio set.
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The BN-58 is one of the first small receivers that was completely
transistor-based and featured very low power consumption.
The double conversion superheterodyne receiver has an IF of 1.635 MHz
and covers 2.5-24 MHz divided over two ranges, selectable with the
second knob:
- 2.5 - 9.1 MHz (green)
- 9.1 - 24 MHz (red)
The receiver features permeability tuning (coil tuning), similar to
Collins receivers, and had a separate tuner for each of the above ranges.
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Because the permeability tuning is mechanically calibrated,
the frequency scales are nearly linear. Each tuner has its own tuning
coil that can be adjusted by means of a fold-out crank; one at either
side of the unit.
The image above shows both cranks in their operational position.
Another example of a receiver that uses permeability tuning is the
WWII American RBZ Receiver.
Power for the FE-8 is supplied by the internal 6V/225 mAh battery,
that can be charged with the supplied mains charger.
Furthermore, an external 6V DC source can be connected to a 2-pin LEMO
socket at the rear of the unit.
In full operation the receiver consumes no more than 8mA.
Also at the rear is a small coaxial LEMO socket that allows connection
of the side-tone cable from the transmitter.
Audio is delivered into 2000 Ω headphones that can be connected
to the 2-pin socket at the far right of the front panel.
Volume is adjusted with the rightmost knob.
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The images above give a clear view of the various control of the FE-8
receiver. Please note the two
notches on top of the unit
that could be used to 'feel' the currently selected band.
In the image, the green band is selected (2.5-9.1MHz) and hence
the rightmost notch protrudes the top of the case to indicate the use
of the green scale. When both notches are 'in', the receiver is 'off'.
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Below is the block diagram of the FE-8 receiver, which is partly
based on the work of Helmuth Meyer (DJ2EI) [1].
At the left are the two different tuners (one for each frequency range).
The first local oscillator and mixer are inside the tuner and produce
an IF1 at 1.635MHz. This signal is mixed with the 2nd IF oscillator
at 1.180 MHz. It produces a 455kHz signal that is amplified
and fed to a detector. The output of the detector is amplified to a suitable
level for 600-4000 Ω headphones. For the reception of CW (morse),
the signal of a switchable BFO is mixed with the 455kHz signal in the 3rd
IF amplifier. In the leftmost position the BFO is turned off.
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The filter between the 2nd mixer and the IF amplifier
is a mechanical Collins band-pass filter
which is just 3.1 kHz wide.
In the above block diagram, the two tuners are each simplified to a single
block. A more detailed block diagram of a single tuner is given below.
Each tuner is in fact a very complex device with multiple permeabilty
tuning coils, resulting in a nearly linear scale. Turning the tuning
crank, moves the ferrites in and out of the coils.
In order to get rid of any linearity-errors, a sophisticated
mechanical correction adjustment is present. Please check the images below
to see this wonderful piece of engineering.
An adjustable 'glide path' that is sensed
by a 'finger' which in turn moves a second ferrite. The glide path
represents in fact the correction curve for the frequency scale.
Never alter the adjustments of this path.
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The FE-8 can be powered by an internal 6V battery,
that consists of five stacked 1.5V NiCd cells. As the original battery is
no longer in production, it may be difficult to find a replacement.
It should be relatively easy however to create a good alternative
from existing 1.2V NiMH cells.
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The FE-8 can also be powered from external 6V DC source that should
be connected to the power socket at the rear of the device, close to
the battery compartment. This sockets needs a
2-pin LEMO connector
of which both pins are used for the plus connection, whilst the
shield is used for the ground (negative) contact.
The image on the right shows the charger that was
supplied with the FE-8. It allows the 6V battery to be charged directly
from the 220V AC mains. The battery is placed inside the outer shell,
which is then fitted onto the charger.
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The complete assembly can then be inserted into a standard wall socket.
Once the battery is full, it can be placed inside the battery
compartment of the FE-8 again. Alternatively, the battery can be charged
directly inside the FE-8 by supplying a slightly higher voltage (7.2V)
to the external DC socket at the rear.
The same type of 6V stacked battery is used in the calibrator
(see below).
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The BN-58 was a very sensitive receiver with a nearly linear scale,
making it easy to tune it to the desired frequency.
Nevertheless, it had to be calibrated from time to time.
This was done by means of the external calibrator shown
in the image below, which is in fact a frequency marker.
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Inside the device is a so-called comb generator [4]; a device
that generates multiple harmonics from a single base frequency,
all of which are identical in strength. When used with a rounded
base frequency (e.g. a 1 MHz crystal) it produces a reference signal (marker)
at regular (1 MHz) intervals. The device is constructed in such a
way that its signal is rather weak (typically -60dBm or lower),
so that the sensitivy of the receiver can be checked at the same time.
The device has two internal reference crystals plus an external one
that can be inserted in the crystal socket on top of the device.
At the front is a three-position rotary switch
with three settings, marked I, II and III.
It is used to select the mode of operation:
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- 100 kHz
This setting produces a -80dBm marker signal
at 100 kHz intervals.
- 1 MHz
This settings produces a -60dBm marker signal
at 1 MHz intervals.
- Crystal
In this mode, the external crystal socket on top of the device is used.
It can be used with any arbitrary frequency that is within the range
of the receiver. We've tried, for example, a standard amateur frequency
crystal of 3.575 MHz, which generates
a marker at 3.575 MHz, 7.150 MHz, etc.
In this mode, the signal strength depends on the crystal's activity.
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