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Transmission Security Key Fill Device

The MX-18290 is a small military-grade ruggedized electronic device that is used for transferring frequency hopping tables into compatible devices, such as the SINCGARS radio sets. This is often called ECCM (Electronic Counter Counter-Measures). It is also known by National Stock Number (NSN) 5895-01-270-3935.
It's case closely resembles that of the KYK-13 but differs from that device as it can only be used for the transfer of the Transmission Security Keys (TSK), consisting of the Frequency Hopping Tables (FH) and channel lock-out information. It can not be used for transferring the Transmissiton Encryption Keys (TEK). For the latter, a KYK-13 or similar is needed.

The MX-18290 roughly measures 15 x 8.5 x 4 cm and is made of die-cast aluminium. At the rear is a small battery compartment that takes a standard 6V BA-5372/U battery.
View of the controls and the left side of the unit. The key input is on the right and the output is on the left.

The device has two connectors (one at either side). The two connectors are male/female pairs of the 6-pin U-229 connector that is commonly used for the connection of voice equipment (microphones and handsets). The NSA uses the same connector for their fill devices. Although one end of the MX-18290 can be connected straight to the fill input of the device that needs to be filled (e.g. a SINCGARS radio set), it is recommended to use a short dedicated 1:1 fill cable.
Like the KYK-13 it has two rotary switches and a recessed push-button at the centre. The push-button is used to initiate a fill or transfer. Just above the initiate button is a green CHECK LED. The topmost rotary is the MODE-switch, controlling the operation of the device. It has three positions:
  • OFF
  • ON
  • ZA (Zeroize All)
The lower rotary is the ADDRESS-selector. It has 16 positions:
  • 1 thru 13 - 13 different frequency hopping sets
  • T1 and T2 - TSK (control the order of the frequency hopping sets)
  • A (All) - load of fill All keys
After connecting the filler to a compatible COMSEC device, keys (i.e. frequency hopping sets) can be loaded individually, by selecting the propriate address (1 thru 13) and subsequently pressing the initiate button. Two complete hopping tables (i.e. the order of the frequency hopping sets) can also be transferred individually (T1 and T2). Setting the MODE-switch to 'A' and pressing the initiate button, will load all keys into the connected device.

In the event of capture by an enemy, the keys can be purged by setting the mode selector to ZA (Zeroize All) and pressing the initiate-button simultanenously.
The MX-18290 can easily be opened by removing the 6 screws from the left panel. Once opened, the solder side of the Printed Circuit Board (PCB) becomes visible. The PCB is held in place by another 6 screws and connects to the rest of the device with a 30-pin connector. After removing these 6 screws, the PCB can be removed by pulling it out of the connector.
The MX-18290 contains only one PCB. When removed, the other parts (switches, LED, connectors and battery compartment) become visible. They are all connected to a large green 30-pin connector by means of a so-called flex PCB. The advantage of using flex PCB rather than just a simple bundle of cables, is the lower weight and easier manufacturing (and hence lower cost).

The PCB contains all active (electronic) parts. The 6th image below gives a good view of the component side of the PCB.
The interior of the device after removing the PCB. The connectors and controls are interconnected with a flex PCB.

At the left is the Harris controller. Below it are the EPROM and two RAM chips. The keys are stored inside the RAM chips and are retained as long as the 6V battery is present (and connected). Removing the battery, or removing the PCB from the case, will disconnect power from the RAM chips and hence delete the keys. The keys are also purged when the user sets the MODE-switch to the ZA position (Zerioze All) and presses the initiate-button simultaneously.
View of the controls and the left side of the unit. The key input is on the right and the output is on the left. View of the controls and the right side of the device, holding the lid to the battery compartment. PCB bottom perspective view View at the solder side of the PCB after the lid is removed. The interior of the device after removing the PCB. The connectors and controls are interconnected with a flex PCB. On the left is the (Harris) controller. Below it are the EPROM and the two RAM chips. View of the (empty) battery compartment after the lid is removed.

Memory of the MX-18290 can be preserved with a standard military 6-Volt Lithium Manganese Dioxide battery BA-5372/U. Note that the prescribed battery type, cast in the battery compartment, is BA-1372/U. This is the earlier Mercury-based battery with the same voltage that has since been replaced by the better BA-5372/U. This battery is available from a variety of sources.

The image on the right shows an example of a suitable battery. Please note that the shape may be different.
Typical 6-Volt BA-5372/U battery

Further information

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