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Clandestine receiver
The Mk.328 is one of the first fully transistorised miniature receivers that
were used for special purposes. It was developed by HMGCC (GCHQ) in the UK
and was introduced in 1970. It was probably intended as the successor
to the 1954 Mk.301 that was based on miniature valves.
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The receiver has a rather unusual 'modern' look and feel. It has no pluggable
coil packs and is completely self-contained. It even has space for two
6.75V Mercury cells (Mallory TR165), but it can also be connected to an
external PSU (10.5-16V DC, 13-18mA).
The receiver has a sensitivity of 3-25µV at 1mW AF output, depending on the
frequency band in use. Output power is about 1mW into 2Kohm headphones.
Furthermore, it has a separate (22Kohm) output for the connection of an
external (tape)recorder.
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It's a single conversion receiver, with switch-selectable band-pass filters
before and after the RF stage, a local oscillator, a mixer, a 3-stage IF
amplifier, a detector, and AF amplifier and a BFO oscillator. It also has
a built-in 250kHz/1MHz oscillator that can be used to calibrate the scales.
Frequency coverage is from 2.5 to 30 MHz in 5 ranges, each with its own
colour coding:
- 2.5 - 5MHz (orange)
- 5 - 10 MHz (green)
- 10 - 15 MHz (yellow)
- 15 - 20 MHz (red)
- 20 - 30MHz (white)
The receiver was distributed with some accessories, such an antenna, headphones,
instruction booklet, etc. The complete kit was packed inside a polytene
box, such as the one shown below.
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Inside the box, the various units are held in place by polystyrene foam.
The blue receiver is visible in the right, whilst the left compartment holds
a transparent plastic box with the additional accessories.
The high-impedant headphones (2Kohm) are placed on top of the accessory box.
In the middle of the box is the telescopic antenna that has a rather
unusual M4 thread screw at the bottom, allowing it to be bolted onto the receiver
(see the pictures below).
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The user had the option to use the telescopic antenna (screwed into a terminal
at one of the corners of the receiver), or a supplied wire antenna. In the latter
case, the receiver also needed a proper connection to the gound (earth).
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The following accessories were present:
- Receiver
- Telescopic antenna
- 2-way headphones (in-ear)
- 2 Mallory mercury cells (6.75V each)
- Instruction booklet
- External battery lead
- Earth lead
- Wire antenna
- Ear clip
- Jumper clip (?)
- Two different recoring cables (Lemo and Uher)
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The receiver is also known as Radio Receiver 328R or as
the complete station UK/TRR-328.
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- HMGCC, Mk 328 Receiver User Handbook
UK, National publication No. 249. Part of the Mk.328 package.
- Louis Meulstee, Wireless for the Warrior, volume 4
ISBN 0952063-36-0, September 2004
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© Copyright 2009-2011, Paul Reuvers & Marc Simons. Last changed: Tue,12 Apr 2011.22:37:38
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