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Motorola MX-300
Handheld radio with digital voice encryption - this page is a stub

The MX-300 was a handheld radio, developed by Motorola in 1975. Many different variants of this radio were developed, incuding VHF, UHF and SHF versions, ruggedized versions, crystal operated channels, versions with a frequency synthesizer, and optional Digital Voice Encryption.

There are many different variants of the MX300, making it difficult to describe it features. The are versions for 4 frequency bands (VHF-L, VHF-H, UHF and SHF) and there were at least 3 different case models. Furthermore, a range of options was available, inluding a frequency synthesizer, channel scanning and digital voice encryption.

The image on the right shows the MX300-R, which is the ruggedised intrinsically safe model. The outer 'skin' of this model is made of rubber, but as it is close to 40 years old now, most of the rubber has become stiff and brittle.
  
MX300-R Control panel

The MX300-R was developed especially for military use and special operations. It is significantly different from the other MX300 models. Not only is the outer body covered in rubber, the internal frame is different as well and some parts and accessories are not interchangable with the rest of the MX300 series. The radio is completely black, as the normal models were too shiny at night.

The MX300 was available with fixed CTCSS 1 (called PL 2 by Motorola), with MDC signalling, with Digital Private Line (DPL) and with DVP 3 or DES 4 voice encryption. It was a popular police radio throughout the 1970s and 80s, until it was succeeded by the Motorola SABER series in 1989.

  1. CTCSS = Continuous Tone-Coded Squelch System.
  2. PL = Private Line ™.
  3. DVP = Digital Voice Protection ™.
  4. DES = Digital Encryption Standard.

MX-300-R without antenna MX300-R Control panel MX300-R Control panel Crypto/Plain selector Accessory socket MX300-R
Models
  • MX-300
    This is the standard version of the MX300. In most cases it has a silver body and a silver control panel with flat knobs. Depending on the version and options however, the layout of the control panel may vary. The radio has 2, 4, 6 or 8 channels, each of which is defined by installing the appropriate crystal. Check the Factory ID to see which model and version you have, and which options are installed.

  • MX-300-S
    This is the synthesized model of the MX300. Rather than installing RX and TX crystals for each channel, the frequencies are stored in a PROM 1 (later in an EEPROM) 2 , organised in 4 banks of 12 channels each. Depending on the variant, 2, 4, 6, 8 or 12 channels are selectable. Furthermore, also depending on the variant, an additional rotary switch might be present to select up to 4 channel banks (marked A, B, C and D). Some versions had a scan option. Digital voice encryption was also available as on option.

  • MX-300-R
    This is the ruggedized version of the MX300. It has most of the features of the MX300-S, but is housed in an intrinsicaly safe enclosure of which the outer skin is cast in rubber. As rubber is a natural product, it might lose some of its properties over time and become stiff and brittle. This model has different knobs on the control panel, which are also made of rubber (similar to the ones used with the later Motorola SABER radios).
  1. Programmable Read-Only Memory (one-time programmable).
  2. Electrically Erasable Programmable Read-Only Memory.

Versions
The MX300 was available for the 4 different frequency bands listed below. It should be noted however, that a single radio could not operate the entire frequency range for which it was designed, but rather a 2 to 4 MHz segment of it. This is often referred to as the Band Split by Motorola. The exact band split can not be determined from the Factory ID, but only by inspecting the reference numbers on each of the internal modules. The following band-versions are known:

  • MB
    This version is for the 68-88 MHz MIDBAND, also known as VHF-L or 4-metre band. This frequency band was widely used by the Police in most countries for many years but has since been abandonned. In some countries, a small segment around 70 MHz has now been allocated for use by Radio Amateurs (HAMs) in some countries [4].

  • VHF
    This version is for a 3 to 4 MHz band split in the 136-174 MHz range, also known as VHF-H or 2-meter band. This band was very popular with the police and other public serives until the arrival of digital radio. Some band-split variants can be converted for use by Radio Amateurs operating in the 144-146 MHz band (148 MHz in some countries).

  • UHF
    This version is for a 2 MHz ban split in the 403-470 MHz band, which was very popular with the police and other public services until the arrival of digital radio. It was also used by the Militry for so-called Special Operations (Special Ops). Some band split variants can be converted for use by Radio Amateurs operating in the 70 cm band (430-440 MHz).

  • SHF
    This version is for use in the 800 MHz band and was only available with fixed (crystal operated) frequencies. It is also believed to be the first radio that was available in a trunking version.
Note that the versions for the first three bands (MB, VHF, UHF) were also available as synthesized variants. The 800 MHz was only available with fixed (crystal operated) channels.

MX-300-R
The image below shows the controls and features of a typical MX300-R radio as it was used by the Dutch armed forces during the 1970s and 80s. The radio shown here has 12 channels and has a rather long squelch adjustment. Furthermore, this radio has a DES encryption module fitted.


Factory ID
There are many different models, versions and variants of the MX300-series. The exact version can be determined by decoding the Factory ID that is printed on a label at the back of the radio. The diagram below shows a typical Factory ID, but it should be noted that the last two letters are optional and my not be present on your radio. They used to identify Revision and Package.


Each position of the Factory ID identifies a single feature or configuration of the radio. At the moment, not all positions are known. The ones that are known are listed below. If you have additional information, please contact us.


Product type
H Handheld
Z Special product

  

Output power
2 1W
3 2.5W (VHF), 2W (UHF), 1.5W (SHF)
4 6W (VHF), 5W (UHF)

  

Frequency band
2 MB: 68-88 MHz
3 VHF: 136-174 MHz
4 UHF: 403-470 MHz
5 SHF: 800 MHz

  

Channel type
A Crystal operated
S Synthesizer

  

Encryption
A No encryption
X Digital encryption

  

Unknown parameter
U ?

  

Squelch type
1 Carrier
3 PL - Private Line (CTCSS)
6 DPL - Digital Private Line

  

Channel spacing
0 Wideband (15 kHz deviation)
1 Narrow band (5 kHz)

  

Channel selector
2 2 Channels
4 4 Channels
6 6 Channels
8 8 Channels

  

Unknown parameter
0 ?

  

Revision
A Original revision

  

Package
- (blank) Warranty replacement radio, bare radio
N Complete package, with antenna and battery

  

Memory modules
  1. NLN5096A
    PROM
  2. NLN5096B
    PROM
  3. NLN5096C
    EEPROM
  4. NLN5096D
    EEPROM
Programming
In the synthesized version of the MX-300 (S in the 4th position of the Factory ID), the RX and TX frequencies are stored inside a PROM or EEPROM. There are organised in 4 banks of 12 channels each, or 16 channels each on some special product (SP) variants. The channel information can not be programmed with an old IBM-compatible computer (as with later Motorola radios), but only with a Motorola R-1800 programmer 1 [2][3].

  1. R-1800, R-1801 and R-1821 suitcase programmer with suitable board and software are all suitable for programming the MX-300 [3].

Connections
The MX300 has an accessory socket at the left side panel, just below the control panel and above the PTT. On the ruggedized model (MX300-R) it is covered by a protective rubber flap. The socket is used for the connection of a range of microphone/speaker and other accessories. On versions with built-in digital encryption, this socket is also used for connecting the key variable loader. The layout of the socket when looking into it whilst the radio is standing up straight is as follows:

  1. PTT (connect to ground)
  2. Speaker audio (with pin 10)
  3. TX audio in (microphone)
  4. Line output (audio before volume control)
  5. 7.5V
  6. RX distriminator audio
  7. Spare
  8. Spare
  9. Ground
  10. Speaker audio (with pin 2)
References
  1. Mike Morris, Robert Meister, Motorola MX-Series Related Information
    Repeater-Builder Website. January 2007 (updated 8 May 2015). Retrieved June 2015.

  2. Brinkley Electronics, Motorola MX Portable FAQ
    Retrieved June 2015.

  3. Batlabs, The MX-300S/R or Scorpio Series
    Retrieved June 2015.

  4. Wikipedia, 4-meter band
    Retrieved June 2015.
Further information
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Crypto Museum. Last changed: Saturday, 11 July 2015 - 08:02 CET.
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