Antenna - Signal Acquisition

Normally the TSCM specialist will use several types of antenna or ridgedwave guide to search for eavesdropping signals while performing TSCMservices. This equipment often includes various type of loop probes,omnidirectional whips, discones, log periodic, and microwavewaveguide.

The most popular "band splits" and matching antenna are as follows:

Range	Antenna Type	Comment
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 MHz	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 anomalyis identified. The antenna is then moved towards to suspect emission tofurther pinpoint the source. This works well for signals in the VHF/UHFrange between 50 MHz and 1 GHz. For signals above .5 GHz the energy isbest collected by slowly moving a ridged waveguide over the suspect area.

The signal usually passes from the antenna or waveguide then into apreselector to isolate the signal further. This preselected signal isthen passed to a preamplifier to further enhance detection.

Dual ridge waveguides typically act as their own preselector, and onlyrequire a preamplifier (or mixer) before passing the signal to thespectrum analyzer.

A transient limiter is also utilized to couple the spectrum analyzersinput directly into the power lines or telephone lines to assist in thedetection of carrier current and VLF devices.

The preselector, preamplifier, and transient limiter all provideprotection against high voltage and RF overload, thus protecting thespectrum analyzers sensitive front-end.

Gain parameters are commonly used to model the performance ofboth and transmit and receive antenna, but Antenna Factors arenormally only used to model the performance of a transmitantenna (which are more precise than receive only units).

While it may seem odd to specify AF for a receive antenna itstarts to make sense when you are using calibrated EMC antennafor all TSCM procedures.

Of course antenna factors increase with frequency (as doesgain), and remember that Antenna Factor is different fromTransmit Antenna Factor (so be careful). Antenna Factor iscalculated as AF = Electric Field/Voltage applied to antenna andis normally expressed in dB.

Remember that while Gain is commonly used to describe thedirectional response, AF is used to describe how "clean" theantenna is, and to describe its efficiency as a transducer.

The high threat VHF band may be checked using an antenna factorof 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. Abiconical 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 dBfrom 300 MHz to 1 GHz. A log periodic antenna works well withinthis frequency band.

At frequencies above 900 MHz it is desirable to use an antennawhich offers a factor of at least 25 dB 1/m, and 30 dB 1/m above2 GHz. Antenna gain should be at least 8-10 dB above 900 MHz (again of at least 15 dB is preferred). A gain of at least 15 dBis recommended between 1.2 GHz and 3 GHz. A broadband duelridged waveguide or log periodic antenna works well within thisfrequency band).

From 3 GHz to 12 GHz an antenna factor of between 30 to 40 dB1/m is good, but anything above 12 GHz requires at least 40 dB1/m of antenna factor or it will be virtually impossible todetect the signal. Antenna gain should be at least 8 dB overthis range. A gain of at least 20 dB is recommended between 3GHz 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 beconsidered. A gain of at least 50 dB should be used when dealingwith frequencies in this range.

The antenna being used must be operated in both a horizontal andvertical polarized position, and also in a 45-degree diagonalposition for optimal signal detection. A professionaleavesdropper will often install their antenna using horizontalpolarization to minimize possible interference or detection.

Left and Right Handed Polarized signals should be checkedbetween at least 900 MHz and 12 GHz using an antenna factor ofat least 25 dB 1/m and a gain of 2-4 dB. Remember that you willget a polarization offset loss figure that must be taken intoconsideration when using a linear polarized antenna. It is OK tomeasure circular polarized signals with a linear polarizedantenna, but you will need to apply compensation to themeasurement.

The number of antenna azimuth and elevation positions used willof course be directly related to the gain of the specificantenna.

A good rule of thumb is that in a 10-meter by 10-meter squareroom in an office environment to use at least 16 steps (22.5degrees) along each axis for every 10 dB of antenna gain. For atypical log periodic antenna (with 5 dB of gain) this wouldresult in 64 measurement positions for each polarization for atotal of 320 positions (assuming horizontal, vertical, diagonal,LHCP, and RHCP polarization). Needless to say a small computercontrolled antenna positioning system is most helpful.

When performing the RF segment of a TSCM survey a search grid of10*10 foot is commonly used. Also, all cables are kept as shortas possible and only low loss cables are used (N Type arestrictly used for anything below 3 GHz, SMA or equiv. foranything above 3 GHz). Low noise preamplifiers can (and should) beused as much as possible as the primary concern is to collect asmuch of the suspect signal as possible.

Condor Systems

AS-106 Compact, Broadband Spinning DF Antenna
The AS-106 is a compact, broadband spinning DF antenna system measuringonly 14" by 17" and weighs only 20 pounds. Frequency coverage is from500 MHz to 18 Ghz, (18-40 Ghz via an optional frequency extender). Theantenna may be controlled from either a PE-140 pedestal, or C-8101antenna controller. Very popular due to the small footprint, lightweight, and excellent beam width.

AS-105 Broadband Spinning DF Antenna
The AS-105 is a compact, broadband spinning DF antenna system measuringonly 19" by 24" and weighs 50 pounds. Frequency coverage is from 500 MHzto 18 Ghz, (18-40 Ghz via an optional frequency extender). The antennamay be controlled from a PE-105 pedestal controller. Popular for signalinterception and space domain/DF measurements (but it's a bit heavy forthe 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 40Ghz. The antenna may be controlled from a PE-105 pedestal antennacontroller. Very popular due to the very wide bandwidth, and integralthreshold detector.

CS-9184/WJ-49184 Millimeter Wave Spinning DF Antenna
This systems provides a compact (22" * 15") spinning DF antenna systemwhich does not utilize rotary joints. The entire system weighs justunder 40 pounds, and is controlled via the C-861/WJ-49861 controller anddisplay. Features include a series of interchangeable feeds whichprovide coverage from 8 GHz to 110 Ghz (40-60, 60-90, and 75-110 are themost desireable). This system is typically used along with a "low-band"DF system such as the AS-135, which allows frequency coverage ofmicrowave 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. Theantenna system features three axis of control (elevation, azimuth, andpolarization). Frequency coverage is 1 GHz to 18 GHz (18 Ghz - 40 GHzwith an optional frequency extender) and may use either a 1 or 2 footdish. The system is controller via a C-8130 antenna control unit, and maybe "remoted" via fiber optic control lines. The system measures only 43"* 34", weighs just over 88 pounds, and is typically operated from atransit case.

AS-151 Deployable Microwave Antenna
The AS-151 is a 1 GHz to 20 GHz 36 inch reflector and feed assemblywhich utilizes a precision azimuth positioner. The antenna may be set upin only two minutes, and is very easy to set up. The sighting scope is areal asset when attempting to locate the location of suspect RFenergy.

AS-48410 Dual Polarized Quad-Ridged Horn Antenna
Pyramidal horn with two orthogonally placed SMA feed points, andfrequency coverage from 750 MHz to 4.5 GHz. This antenna may be usedalone, or with a 36 inch dish to intercept and detect many of the 900MHz to 2.8 GHz covert video eavesdropping devices. This antenna is alsocommonly used for non-linear junction detection (up to 40 watts output).

AS-48603 Spiral Antenna
Extremely broadband planar spiral and helix combination antenna in asingle housing with frequency coverage from 250 MHz to 2 GHz. Normallyused in conjunction with a AS-48605 spiral antenna. Primarily used todetect ultra-low power microwave video and burst transmitters.

AS-48605 Spiral Antenna
Extremely broadband planar spiral and helix combination antenna in asingle housing with frequency coverage from 700 MHz to 18 GHz. Normallyused in conjunction with a AS-48603 spiral antenna. Primarily used todetect ultra-low power microwave video and burst transmitters.

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