Hand Emplaced Expendable Jammer
Model No. 4286-031

 VHF Low Band Jammer

Brooke Clarke 2008 - 2013

HEXJAM VHF Low Band Jammer
HEXJAM VHF Low Band Jammer
HEXJAM Control
                    Control Panel HEXJAM Control
                  Panel close up
                    Control Panel
HEXJAM Battery



During W.W.II a number of communication (and RADAR) jammers were developed, but the com jammers ended up on shelves not being used.  That was because we were listening to the messages the enemy thought were secret because they were using cryptography.  When you can break someone's crypto then it's best to not jam but instead listen.

I used to have a cylindrical jammer that may have been made from paper or cardboard that was varnished.  It had a knob on the end, maybe tied to a timer.  I think it worked using batteries and a spark gap.  Brown and/or yellow color.

This is a VHF Low Band Jammer covering 20 to 90 MHz with a range of 1 km.  It's powered by a BA-5590/U battery for 4 hours.
The three rotary switches set a time delay of up to 29 Hours.  Or the jammer can be turned on using a switch at the end of some field wire.

Note the two wings when folded closed form a box to enclose the jammer and when opened help to stabilize the whip antenna.

Photos provided by Pat L.

Joint Counter Radio-Controlled Improvised Explosive Device Electronic Warfare ( JCREW)

How IEDs Work -

CRS Report "Improvised Explosive Devices (IEDs) in Iraq and Afghanistan: Effects and Countermeasures" RS22330.pdf - IED Countermeasures Equipment (ICE) and Warlock are jammers that disable radio receivers. 

June 5, 2009 - Sierra Nevada Corp awarded $36M contract for JCREW systems
Jan 16, 2008 - Northrop Grumman Corp $16M contract for JCREW systems

Motorola VHF Jammer

There is a very similar Motorola jammer for UHF, this is the VHF version.
The battery box holds three each BB-390 or BB-590 batteries and (as can be seen by the connector in the photo below) a charger for those batteries.
There is a trap door on the bottom of the chassis (facing down to the top for the battery box) under which is a socket for a EEPROM.  What it controls is TBD.

Motorola VHF
The Type-NF connector is marked ANT and the BNC jack nestled in the heatsink fins is marked EXT ANT.  The implication is that the ANT connector is for a  wave whip and the EXT ANT connector is for an antenna matched to 50 Ohms, like the OE-254.  Note it's very difficult to use a simple whip antenna for the VHF low band (30 to 90 MHz) so they typically have a network containing a load lowering the efficiency.
Inside the
              Motorola VHF Jammer
The uP board has been removed from the bottom slot and is shown below.
There are positions for two other boards, but no sockets on the mother board for them
so they may be used in a different model like the UHF version.
The removable board with the metal can on the left appears to be a synthyzer.
The black box at the right bottom (above the guide pin) is a 15 to 32 VDC In to 12.0 VDC
Output conveter rated for 700 ma, i.e. the total power consumption of this jammer is about
8 Watts to the output power maybe 4 Watts average.

Above the syn board is a box containing the power amp.

The power Amp has 7 lines plus 2 (power & ground).

The AC line connector on the battery box is a:



chassis gnd


to 6A fuse
Battery Box is Motorola p/n:
It can hold two or three BA-5590/U Primary batteries, or
two or three BB-590/U Ni-Cad batteries.  \

There are no contacts for the thermistors in the BB-390 Ni-MH so these should not be used.
Motorola VHF
              Jammer & Rechargable Battery boxMotorola Jammer micro Processor

The 40 pin chip at the left is an MC 146805E2 uP.  It's program is in the MC27C64 just
above the Zero Insertion Force socket that holds the parameter EEPROM chip.  Just below
the ZIF socket is a 160 kHz unit oscillator and a 74HC390 dual decade divider.  The 40 pin chip on the right is an MC146823 RAM and the 24 pin chip in the lower right corner is an MC 146818 timer.

The 8 pin DIP in the upper left is an MM5437 Digital White Noise Generator.  Probably a modulation source or frequency setting source driving the synth board.
The 8 pin DIP at the left center is a MAX638 switching regulator to reduce the board 12 Volts to some lower voltage for the ICs.


The box on the left has 9 traces going to it on the top and 2 traces on the bottom (to 145158-8 Fin &-12 Mod.  The 16 pin DIP about in the center of the board is an MV145158 Serial Input Dual Modulus PLL Synthesizer aimed at the TV market, AM/FM and 2-way radios.

Pin 1 of the 145158 is fed from a 14.4 MHz unit oscillator in the upper right of the photo.  The serial clock and data comes from the uP board.

Motorola VHF Jammer Synthesizer
Motorola VHF Jammer Synthesizer board


Modern Communications Jamming: Principles and Techniques  By Richard Poisel


3600685 Apparatus and method for interfering with radio communications, Doyle William C, Itek Corp, Mar 20, 1969, Aug 17, 1971, 455/1, 342/15
                10 kHz Rx/Tx jamming cycle allows recording speech for later analysis while jamming enemy

Selective disruptor for voice modulated communications, Vincent J Nardozza, Marvin R Clinch, Secretary Of The Air Force,
                Oct 22, 1969, Jun 21, 2011 (Top Secret for 42 years!), 342/15, 455/1, 342/13
                The original voice signal is recorded and then played back after a delay. 
allows recording speech for later analysis while jamming enemy


Shaping the Electronic Battlespace: The HEXJAM - Engineer Bulletin August 1996
Using the MC145158 PLL Frequency Synthesizer
Tactical Radio Jammers

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