With Two Way Radio for a long time now, one of the biggest limiting factors when running a covert surveillance operation has been the radio’s antenna.
Unlike the internal antennas on mobile phones, two way radios antennas need to be external.
This is partly due to the fact that phones only need to communicate with the nearest cell site.
Another factor is that the frequencies used in cellular phones are far higher than PMR frequencies, so antennas can be made much smaller.
After many months of intensive research, one manufacturer has developed a highly efficient, totally covert antenna for use in professional surveillance scenarios.
The main problem was to relocate the antenna, which radiates the electromagnetic waves, away from the main mass of the human body to increase radiation efficiency.
It was also desirable to reduce the bulk of the antenna to an absolute minimum, so it could be concealed beneath thin clothing. This would allow use in situations where thick coats and jackets may draw attention to the surveillance operative. (Such as in warm climates).
The ingenious solution of attaching an (almost) invisible antenna to the body was to simply paint the antenna onto the skin. The connection to the radio was also needed and the final low-loss design resembles a clothing pop fastener along with a strap.
Initially, there were problems associated with placing an open radiating element directly against the skin.
Unfortunately, a small number of minor injuries occurred before the complex calculations on safe transmit power levels at both VHF and UHF were completed.
Once the prototype body paint and connector system was developed and safe radiation calculations were finished (and test subjects skin had healed sufficiently), a number of body locations were identified as possible antenna sites.
Trials on the upper leg (Femur) and lower leg (Tibia) proved unsuccessful.
Test results on the upper leg were erratic. The reason was eventually found to be variation of pocket contents. (If keys or loose change were carried in the pocket, there was a detrimental effect on antenna performance).
The lower leg , being fairly close to the floor, gave poor results on range tests. Increasing transmit power simply caused radiation burns (again!) with no appreciable increase in performance.
The lack of range problem experienced with the lower leg prompted investigation into using the highest point of the human body, the skull.
Users were obliged to wear some type of hat or headgear to conceal the “Paint Antenna”. (A surveillance operative wearing a hat would draw attention in any number of situations).
Test subjects also complained of blurred vision and/or “ringing” in the ears, whilst transmitting. Severe headaches also seemed to be a common after-effect.
There was only one minor problem.
Raising the arm to the horizontal changes the vertically polarized radiation pattern to horizontally polarised, which introduces approximately 3dB of attenuation. (Half power).
Fortunately, this should be a minor inconvenience for a professional operative. The only time that it may be a problem is when a sidearm is brought to bear.
The solution to this problem would be for the user to “shoot from the hip”, thus keeping the upper arm in an upright position.
The “Paint Antenna” is supplied as a kit with paint, connector (customised to radio model) and a “paint application chart”.
Because the human body is not standard, the application chart is used to tailor the “Paint Antenna” pattern to a wide variation of BMI (body mass index), skin complexion, muscle tone, arm length and various types of clothing.
Additionally, instructions are included with the chart to design directional paint antennas. These patterns can increase range, but will obviously have to be used with care. (If the operative changes orientation significantly, comms can totally disappear).
The antenna site will also need to be shaved. This is because painted hairs of differing lengths could create an alternating pattern of nodal and antinodal waves. This is known as “interference pattern effect” and has the potential to reduce the efficiency of the “Paint Antenna” by as much as 9dB.
The company is continuing development of this exciting product, and are presently looking into the use of permanent tattooed antennas, disguised as traditional “tribal” tattoos.
Other designs are possible, but there are obviously considerations to be made, to ensure antenna concealment.
In the future the company see the possibility of installing the ultimate covert antenna actually inside the humerus bone itself.
Any (paid) volunteers for trials of this groundbreaking product can initially contact us and we will pass on your details.
(In the interests of full disclosure, we do get a referral fee).
Oh, and happy April Fool’s Day everyone!