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Field-strength meter with frequency counter
3000/C was a mobile frequency counter with built-in field-strength
indicator, developed by Dare Instruments in Woerden (Netherlands) [1]
around 1997 for the Dutch police.
The units were used by the police to determine the frequency of mobile
radio systems used by criminals in order to be able to intercept them.
They could also be used to trace bugs
and find beacon transmitters.
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The unit has the form factor of a standard car radio, so that it could be
built into virtually any vehicle, without attracting too much attention.
It is powered by the 12V car battery (10-15V).
The CR-3000/C has a frequency range of DC to 1 GHz and will automatically
lock onto the strongest signal when in close proximity of a transmitter.
When locked, the 8-digit display will instantly show the
frequency of the intercepted signal. When very close to the transmitter,
the 8-unit LED bar to the right of the display will give an indication of
the field-strength of that signal.
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It is currently unknown how many CR-3000/C units were made, but assuming that
every police district in the Netherlands had between 2 and 4 units, we assume
that approx. 100 units were built. In 1013/2014, the majority of CR-3000/C
units were dumped on the Dutch surplus market. The handheld version, known
as the CR-3000/H, has not (yet) been dumped.
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All controls are at the front panel of the CR-3000/C which
consists of an aluminium panel with a custom-made self-adhesive keypad.
A series of push-buttons at the lower half of the front panel are used
to control the unit. The leftmost button is the ON/OFF switch.
The display has two brightness settings: one for
when the unit is used in bright daylight and one for use at night.
The remaining black buttons (marked with up/down arrows) are for
adjusting the threshold and sensitivity levels of the instrument,
and for adjusting the volume of the acoustic indicator. When a speaker
is connected at the rear, the unit will produce a tone of varying height
depending on the strength of the signal, in parallel with the LED bar
indicator at the front panel.
The image above shows the connectors at the rear panel of the CR-3000/C.
The power socket accepts a wide range of DC voltages (10-15V) and was
typically connected to the 12V battery of a car. Note that the sockets
for the power input and the speaker output are identical.
Do not swap them,
as connecting power to the speaker output will permanently damage
the audio amplifier inside the unit.
The 1/100 output was intended for driving an external PLL,
but it is unclear whether this was ever used.
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The interior of the CD-3000/C can be exposed by removing 4 screws from the
sides of the unit. This allows the upper and lower sections of the case to
be separated, after which the interior becomes visible. The image below
shows the interior or the CR-3000/C, seen from the rear.
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The first impression is somewhat disappointing. One would expect a professional
custom-made instrument like this to be a single integrated design, but instead
it consists of a collection of separate PCBs, that were (probably)
designed for other products and that were reused here.
The front-end
was clearly designed for, say, an HF instrument, and is bolted
to the bottom of the case. To the left of the front-end is a small PCB that
holds the DC power converter and the audio amplifier.
The main unit, mounted at
the left, consists of three stacked and bolted PCBs.
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The upper PCB of the main unit appears to be nothing more than a cable
adapter. The second PCB contains an
Intersil ICM7216D [2],
which is an 8-digit LED display driver / frequency counter. Despite the
rather disappointing first impression however, the unit performs very well
and does exactly what it was designed for. It can still be used as
an intercept or measuring device today.
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The block diagram below gives an impression of how the CR-3000/C works.
The input signal is first amplified with a 2-stage wide band amplifier.
The frequency counter inside the Intersil ICM7216D is suitable for frequencies
between DC and 10 MHz, which is why the input signal has to be divided
by 100 first. This is done by the pre-scaler, who's output is available
at the rear.
The output from the pre-scaler is fed into the frequency counter, which
drives the LED display. The output from the font-end is also fed into
a detector that drives the field-strength LED bar indicator
and the acoustic indicator (speaker).
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© Copyright 2009-2013, Paul Reuvers & Marc Simons. Last changed: Wednesday, 30 April 2014 - 23:43 CET
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