Antenna - Signal Acquisition
Normally the TSCM specialist will use several types of antenna or ridged wave guide to search for eavesdropping signals while performing TSCM services. This equipment often includes various type of loop probes, omnidirectional whips, discones, log periodic, and microwave waveguide.
The most popular "band splits" and matching antenna are as follows:
|100 Hz - 400 MHz||Transient Limiter/RF Coupler||(VLF and AC Mains Devices)|
|3 kHz - 50 MHz||Active HF Loop Antenna||(Directional)|
|9 kHz - 70 MHz||Active HF Whip/Rod Antenna||(Omnidirectional)|
|40 MHz - 1.5 GHz||Discone||(Omnidirectional)|
|70 MHz - 1 GHz||Log Periodic||(Directional)|
|480 MHz - 2 GHz||Crossed Log Periodic||(Highly Directional)|
|1 GHz - 3 GHz||Spiral Log Periodic||(Highly Directional)|
|1 GHz - 8 GHz||Dual Ridge Wave Guide||(with Preamplifier)|
|8 GHz - 18 GHz||Dual Ridge Wave Guide||(with Preamplifier)|
|18 GHz - 26 GHz||Dual Ridge Wave Guide||(with Preamplifier)|
|26 GHz - 40 GHz||Dual Ridge Wave Guide||(with Preamplifier)|
|40 GHz - 75 GHz||Wave Guide/Reflector Plate||(with Preselected Mixer)|
|75 GHz - 110 GHz||Wave Guide/Reflector Plate||(with Preselected Mixer)|
|110 GHz - 325 GHz||Wave Guide/Reflector Plate||(with Preselected Mixer)|
|.5 GHz - 40 GHz||Spinning Parabolic Reflector and Waveguide|
with Dual Polarized Crossed Log Periodic
|(ACES DF System)|
|200 MHz - 3 GHz||Waveguide on Expandable Pole||(Non-Linear Junction Detector)|
A TSCM antenna is normally operated on a tripod until a spectral anomaly is identified. The antenna is then moved towards the suspect emission to further pinpoint the source. This works well for signals in the VHF/UHF range between 50 MHz and 1 GHz. For signals above .5 GHz the energy is best collected by slowly moving a ridged waveguide over the suspect area.
The signal usually passes from the antenna or waveguide then into a preselector to isolate the signal further. This preselected signal is then passed to a preamplifier to further enhance detection.
Dual ridge waveguides typically act as their own preselector, and only require a preamplifier (or mixer) before passing the signal to the spectrum analyzer.
A transient limiter is also utilized to couple the spectrum analyzers input directly into the power lines or telephone lines to assist in the detection of carrier current and VLF devices.
The preselector, preamplifier, and transient limiter all provide protection against high voltage and RF overload, thus protecting the spectrum analyzers sensitive front-end.
Gain parameters are commonly used to model the performance of both and transmit and receive antenna, but Antenna Factors are normally only used to model the performance of a transmit antenna (which are more precise than receive only units).
While it may seem odd to specify AF for a receive antenna it starts to make sense when you are using calibrated EMC antenna for all TSCM procedures.
Of course antenna factors increase with frequency (as does gain), and remember that Antenna Factor is different from Transmit Antenna Factor (so be careful). Antenna Factor is calculated as AF = Electric Field/Voltage applied to antenna and is normally expressed in dB.
Remember that while Gain is commonly used to describe the directional response, AF is used to describe how "clean" the antenna is, and to describe its efficiency as a transducer.
The high threat VHF band may be checked using an antenna factor of at least 10 dB 1/m for signals between 20 MHz and 300 MHz. Antenna gain should be between unity and 4 dB over this range. A biconical antenna works well within this frequency band.
Antenna factors for frequencies above 300 MHz should be between (at least) 15 and 20 dB 1/m. Antenna gain should be over 4-8 dB from 300 MHz to 1 GHz. A log periodic antenna works well within this frequency band.
At frequencies above 900 MHz it is desirable to use an antenna which offers a factor of at least 25 dB 1/m, and 30 dB 1/m above 2 GHz. Antenna gain should be at least 8-10 dB above 900 MHz (a gain of at least 15 dB is preferred). A gain of at least 15 dB is recommended between 1.2 GHz and 3 GHz. A broadband duel ridged waveguide or log periodic antenna works well within this frequency band).
From 3 GHz to 12 GHz an antenna factor of between 30 to 40 dB 1/m is good, but anything above 12 GHz requires at least 40 dB 1/m of antenna factor or it will be virtually impossible to detect the signal. Antenna gain should be at least 8 dB over this range. A gain of at least 20 dB is recommended between 3 GHz to 6 GHz, and at least 30 dB up to 12 GHz.
Above 12 GHz antenna factors of at least 35 dB 1/m must be considered. A gain of at least 50 dB should be used when dealing with frequencies in this range.
The antenna being used must be operated in both a horizontal and vertical polarized position, and also in a 45-degree diagonal position for optimal signal detection. A professional eavesdropper will often install their antenna using horizontal polarization to minimize possible interference or detection.
Left and Right Handed Polarized signals should be checked between at least 900 MHz and 12 GHz using an antenna factor of at least 25 dB 1/m and a gain of 2-4 dB. Remember that you will get a polarization offset loss figure that must be taken into consideration when using a linear polarized antenna. It is OK to measure circular polarized signals with a linear polarized antenna, but you will need to apply compensation to the measurement.
The number of antenna azimuth and elevation positions used will of course be directly related to the gain of the specific antenna.
A good rule of thumb is that in a 10-meter by 10-meter square room in an office environment to use at least 16 steps (22.5 degrees) along each axis for every 10 dB of antenna gain. For a typical log periodic antenna (with 5 dB of gain) this would result in 64 measurement positions for each polarization for a total of 320 positions (assuming horizontal, vertical, diagonal, LHCP, and RHCP polarization). Needless to say a small computer controlled antenna positioning system is most helpful.
When performing the RF segment of a TSCM survey a search grid of 10*10 foot is commonly used. Also, all cables are kept as short as possible and only low loss cables are used (N Type are strictly used for anything below 3 GHz, SMA or equiv. for anything above 3 GHz). Low noise preamplifiers can (and should) be used as much as possible as the primary concern is to collect as much of the suspect signal as possible.
AS-106 Compact, Broadband Spinning DF Antenna
The AS-106 is a compact, broadband spinning DF antenna system measuring only 14" by 17" and weighs only 20 pounds. Frequency coverage is from 500 MHz to 18 Ghz, (18-40 Ghz via an optional frequency extender). The antenna may be controlled from either a PE-140 pedestal, or C-8101 antenna controller. Very popular due to the small footprint, light weight, and excellent beam width.
AS-105 Broadband Spinning DF Antenna
The AS-105 is a compact, broadband spinning DF antenna system measuring only 19" by 24" and weighs 50 pounds. Frequency coverage is from 500 MHz to 18 Ghz, (18-40 Ghz via an optional frequency extender). The antenna may be controlled from a PE-105 pedestal controller. Popular for signal interception and space domain/DF measurements (but it's a bit heavy for the size).
AS-135/CS-2200 Broadband Spinning DF Antenna and Pedestal
The AS-135 is a broadband spinning DF antenna system measuring only 19" by 24" and weighs 75 pounds. Frequency coverage is from 500 MHz to 40 Ghz. The antenna may be controlled from a PE-105 pedestal antenna controller. Very popular due to the very wide bandwidth, and integral threshold detector.
CS-9184/WJ-49184 Millimeter Wave Spinning DF Antenna
This systems provides a compact (22" * 15") spinning DF antenna system which does not utilize rotary joints. The entire system weighs just under 40 pounds, and is controlled via the C-861/WJ-49861 controller and display. Features include a series of interchangeable feeds which provide coverage from 8 GHz to 110 Ghz (40-60, 60-90, and 75-110 are the most desireable). This system is typically used along with a "low-band" DF system such as the AS-135, which allows frequency coverage of microwave threats from 500 MHz to 110 GHz.
CS-8050 Three Axis Spinning DF Antenna System
This is "The Cadillac" of TSCM microwave DF systems with a compact size, high performance, and an excellent performance to weight ratio. The antenna system features three axis of control (elevation, azimuth, and polarization). Frequency coverage is 1 GHz to 18 GHz (18 Ghz - 40 GHz with an optional frequency extender) and may use either a 1 or 2 foot dish. The system is controller via a C-8130 antenna control unit, and may be "remoted" via fiber optic control lines. The system measures only 43" * 34", weighs just over 88 pounds, and is typically operated from a transit case.
AS-151 Deployable Microwave Antenna
The AS-151 is a 1 GHz to 20 GHz 36 inch reflector and feed assembly which utilizes a precision azimuth positioner. The antenna may be set up in only two minutes, and is very easy to set up. The sighting scope is a real asset when attempting to locate the location of suspect RF energy.
AS-48410 Dual Polarized Quad-Ridged Horn Antenna
Pyramidal horn with two orthogonally placed SMA feed points, and frequency coverage from 750 MHz to 4.5 GHz. This antenna may be used alone, or with a 36 inch dish to intercept and detect many of the 900 MHz to 2.8 GHz covert video eavesdropping devices. This antenna is also commonly used for non-linear junction detection (up to 40 watts output).
AS-48603 Spiral Antenna
Extremely broadband planar spiral and helix combination antenna in a single housing with frequency coverage from 250 MHz to 2 GHz. Normally used in conjunction with a AS-48605 spiral antenna. Primarily used to detect ultra-low power microwave video and burst transmitters.
AS-48605 Spiral Antenna
Extremely broadband planar spiral and helix combination antenna in a single housing with frequency coverage from 700 MHz to 18 GHz. Normally used in conjunction with a AS-48603 spiral antenna. Primarily used to detect ultra-low power microwave video and burst transmitters.
| Spectrum Analyzers
| Vector Signal Analysers
| Time Domain Reflectometers
| Antenna | Oscilloscopes | Multimeters | Craft Instruments | TSCM Specific Instruments |
| Non Linear Junction Detectors | Acoustic | Physical Search | Photographic and Imaging |
| Auxillary | Ancillary | Video | Vehicles |
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