All Zap Checker models are easy to use, small, handheld products with internal fixed antennas which require no adjustments. All models employ linear (regular) as well as logarithmic (compressed) amplification and detection. Each model has an analog meter and LED display. (The LED displays are visible from a distance and at night time.)
Most Zap Checkers have an audio output to hear signal strength levels and identify sources by their characteristic sounds. Some products have a switch enabled silent vibrator. The more professional models employ specialized external antennas and, in the case of the ABC 126, a high frequency band that filters out noise and interfering signals to allow for the highly sensitive detection of signals above 1.5 GHz. The ABC 126 also has a USB output connection for distant monitoring, remote powering and accessory switching.
COMMON USERS OF ZAPCHECKER PRODUCTS
Security personnel involved in installing and detecting surveillance equipment, wireless installers and RF networking personnel to optimize hub and satellite sites, confirm transmissions, detect hot and cold spots, measure baseline RF levels, detect and locate RFI, plot radiating patterns, and aim wireless/ communication antennas. Users include amateur radio operators and hobbyists for tuning up milliwatt transmitters, measuring far-field transmitter/antenna performance, determining front to back antenna ratios, plotting antenna patterns, detecting cable leaks and RFI locations, pruning antennas and detecting and locating hidden transmitters during “fox” hunts. Aircraft flight crews and maintenance personnel can use the products to detect interfering devices that could affect flight safety and communications, especially during flight times. Other users are people involved with the maintenance of RF-communications devices (utilities, military, police, fire, construction, data), and those who test, install or maintain RFID, cellular phones, remote-keying and signaling devices. As well as persons interested in measuring levels of radio frequency transmissions for environmental or health reasons.
ARTICLE: RF SIGNALS
Radio Frequency (RF) signal measuring instruments have been a necessary tool for the effective installation, detection and monitoring of wireless devices. RF Field strength meters have been used in this capacity for years for signals below 400 MHz. Special diode-detection apparatus has been used for frequencies up to 1 GHz but become progressively weaker and ineffective at higher frequencies. These diode-detecting devices have previously been the only apparatus available for portable, wideband, high frequency detection. In the security counter-surveillance field, diode-detector based instruments priced above US $2,000 to $15,000 are still the mainstay of wireless detection gear. This heavy, bulky equipment can detect 2.4 GHz bugs only from distances of ½-1 meter away, hence the necessity for security “sweeps” at close distances. Low cost diode detection devices for computer wireless applications have a limited range and sensitivity to them.
The Zap Checker products - using micro-IC technology - introduce a new generation of high frequency RF signal detectors. The zap Checker products are small, handheld ultra-sensitive RF measurement instruments. They span a broadband of frequencies extending from 1 MHz (AM radio) to 14 GHz (twice as high as 802.11a wireless transmissions.) The Zap Checker Model ABC 126 has a sensitivity of -95 dBm in the gigahertz range. It can effectively be used to beyond 14 GHz.
It is relatively easy to make comparative sensitivity measurements at these higher frequencies. Standard 2.4 GHz wireless telephones and microwave ovens make excellent signal sources. Using an operating “sealed” microwave oven, it is common to detect the oven’s 2.4 GHz signal using the Zap Checker products at greater than 10 meters distance. The Zap Checker Model 300 and ABC 126 with directional Yagi antennas can detect wireless 2.4 GHz telephones (10 mw of power) at distances greater than 60 meters. Make a comparative measurement between RF detectors that you may now be using and these Zap Checker products. It becomes quite evident that the Zap Checker products represents a new generation of sensitive, high- frequency detectors.
FICKLE RF SIGNALS
We are continuously immersed in a pool of radio-frequency (RF) signals. (Television, FM, voice and data communications, microwave and radar transmissions; all at different frequencies) are constantly in our environment and have been for decades.
When we are in a room, these RF signals bounce off the walls, ceiling and floor to converge in some regions (hot spots) and leave relatively dead signal areas (cold spots) in other locations. The location of these hot and cold spots is also dependent upon the frequencies involved - the RF signals being reflected, refracted and absorbed depending upon their frequency content. Even in outdoor environments we can measure relative hot and cold spots due to reflections and refractions from buildings, the ground, mountains and even the sky. When using the Zap Checker products you will also notice the change in signal strength due to people and vehicles moving in the vicinity of the beam path.
As a rough analogy, think of a rapid flowing stream (RF signals) flowing over small and large rocks, crevasses and abutments (reflecting surfaces). The clear water is deflected and tumbles in some areas causing opacities and cataracts (hot spots) and also producing regions with lower velocity and almost stagnant flow (cold spots).
Zap Checker products give us the ability to measure RF signals over a broad range of frequencies down to their weak background (ambient) levels. This high sensitivity allows us to detect RF signals almost everywhere, in a fickle manner. Not only are there hot spots, cold spots and intermediate signal levels, but also the levels can change appreciably from one location to the other, only a few centimeters away. Moreover, we can observe changes over time as well (transmissions from a passing police car or utility vehicle, the neighbors’ intermittent use of wireless computer devices, cell phones and wireless phones and microwave ovens, etc.). How can we use the improved sensitivity to our advantage rather than getting confuse with measuring signals everywhere?
HOW TO USE THE ZAP CHECKER PRODUCTS
We can reap the benefits of increased sensitivity in the Zap Checker products by using them in a standard, repeatable manner. First we need to measure the background (ambient) levels of RF signals in the region of interest. Switch the Zap Checker to LINEAR MODE with the antenna switch in the Internal Antenna position. Turn the Zap Checker on by rotating the sensitivity control clockwise and advancing it to a level where the measured background RF signal registers between 10 to 40 on the meter scale. Move around a bit while observing the scale to confirm that the background level is relatively constant at this location. In high-signal, urban areas the Zap Checker may need to have the mode switch set to the Intermediate or even the LOG Mode to avoid overloading the signal reading. In rural, low-signal areas, sometimes almost no ambient signal measurement can be made even with the mode switch in LINEAR and the sensitivity controller on number 10). Once the background RF signal is adjusted on the Zap Checker meter, any signal that exceeds this background level will register as a rise in the signal level and an increase in the red LED illumination.
In the LINEAR mode, even a weak 1 dB signal change above background levels will be detected. In the INTermediate mode, a signal about 8 times stronger will just be detected, but the signal detection range will be extended 8 times to measure stronger signals within the meter’s range. In the LOG mode, the detection range is compressed on the meter scale so that very weak signals to very strong signals (1,000 times stronger than the weak signals) can be displayed on the same scale. The LOG mode is used to measure relative signal strengths between 2 signals or to home-in on a transmitter and pinpoint its position without overloading the meter reading. The LOG mode will register a linear increase in its reading as the signal source is approach. If a move in one direction increases the LOG mode reading, then the movement is towards the signal source and vice versa. The correct direction to the source is recognized by the greatest signal increase as the Zap Checker is moved in different directions.
The LEDs are used to observe the RF signal measurements from a distance or in dim light. For analog signal sources, as the signal measurement gets stronger the green LED gets progressively weaker and the red LED gets progressively stronger. (Both LEDs will be brightly illuminated when a digital signal source is being measured. This is because the rapidly pulsed on and off digital signal registers rapidly in sequence on the red and green LEDs.)
The analog meter registers the average signal level of the digital signal. If a digital signal is pulsed on and off equally in time, the meter scale would measure one half the reading that would be registered if the digital transmission was constantly in the “on” position. This difference in meter reading is particularly apparent when switching from Analog to Digital modes. Digital signals give a “peak” reading which is higher than the average reading in the Analog mode.
Once the background RF signal is detected, we can measure for any radio frequency interference (RFI) at the installation site. If RFI is causing a problem, then switch to the MID or LOG mode and locate the source of the interfering device. Perhaps it can be moved or eliminated.
The Zap Checker products can help to establish optimal transmitting and receiving locations once the interfering signals have been eliminated. Is the chosen location in a Hot or Cold spot? There would probably be trouble in obtaining a wireless connection using a cold spot. On the other hand, hot spots may contain too many other extraneous signals. Use the Zap Checker to choose an intermediate signal location.
Is the transmission with its antenna system working properly? Place the Zap Checker at the receiver site where its LEDs can be seen from the transmitting site. Trigger the transmitter on and off noting the corresponding signal level with the colored LEDs. (An assistant communicating with you using a walkie-talkie will be helpful for receiving sites that are too far away or are not directly observed from the transmitter location). Adjust the wireless link by moving the transmitter (or hub) location a few centimeters or adjusting the remote/receiver location so that maximum signal strength is obtained. Hub and satellite sites are optimized in this manner.
Sometimes a better wireless link can be made by transmitting down hallways or reflecting signals obliquely from corners rather than transmitting through walls or partitions. Remember also to try bounce-communication links from ceiling and floors as well.
With longer distance wireless links or passage through several walls or obstructions, the effective radiating power of the transmitter and/or the sensitivity of the receiver will need to be increased. This can be accomplished effectively with the use of directional transmitting and receiving antennas. RF signals can lose 2-5 dB passing through walls and partitions and up to 10-20 dB passing through concrete. Steel buildings or steel reinforced concrete can attenuate the signal even more.
The Zap Checker Model 300 and ABC 126 are designed for use with either their internal antennas or with switched external antennas. By employing their fixed internal antennas, the meters are sensitive omni-directional RF measuring instruments. Such a self-contained handheld device is ideal for installing and checking the performance of a wide range of wireless products such as computer wireless devices, police and utility communication equipment and RFID systems. Other uses for the omni-directional internal antennas are the detection of cable leaking and also the identification of potential hacker sites outside the intended WLAN area. These identified potential hacker locations can then be minimized by shielding, moving hub/remote sites and RF power management.
The Zap Checker products with internal or external antennas make super-sensitive Wi Fi sniffers. The effective coverage of a Wi Fi system can be mapped from far distances, the hub site optimized for coverage, or the RF signal managed to exclude unwanted users. Denial of service, jamming or radio frequency interference is also detected and the source of the problem localized and corrected.
For general wireless applications (such as the installation of computer WLAN’s, security and surveillance equipment and the detection of covert devices) the ZC 300 and the ABC 126 are often used in conjunction with specific task-oriented antennas.
YAGI DIRECTIONAL ANTENNA
Why are different types of antennas needed for different wireless communications? The effectiveness and reliability of wireless communication links are often dependent upon the antennas that are employed. The government specifies the frequencies and maximum power levels that can be used for different applications. The power levels are limited to low values for computer wireless links, WLAN, Wi Fi and security /surveillance applications. The radiating power from the transmitting system can effectively be multiplied several times by using an appropriate directional antenna system. Similarly, the sensitivity of the receiving system can be increased several fold by the use of a frequency-specific directional antenna system. Hence, by using frequency-specific directional antennas, the effective wireless connection can be extended to long distances.
Directional antennas are used with the Zap Checker products to customize the directionality, sensitivity and frequency specificity of the RF measurement system. A Yagi antenna is used to maximum the sensitivity (and directionality) of the RF signal along the long axis of the antenna. The length of the Yagi antenna generally determines its sensitivity and directionality: with longer antennas being more sensitive at a specific frequency. The handheld Alan Broadband Co. Yagi antenna will increase the sensitivity and sharpen directionality by a factor of 8 times at 2.4 GHz. The Zap Checker/Yagi antenna combination is optimized for the distant detection of low power wireless devices in the 2.4 GHz band. This makes them particularly applicable for such tasks as aiming and aligning antennas for longer distance communications, for detecting signals at a far distance (such as determining which insulator is arcing at the top of the utility pole) or determining the direction to a micro-power covert transmitter (sweep the room from the door).
LOG PERIODIC ANTENNA
The Zap Checker 300 and ABC 126 are also designed for use with a small triangular 1.8 – 6.4 GHz Log Periodic Antenna. The Log Periodic antenna improves sensitivity and directionality by a factor of about 3 times. This antenna is the most popular one for general use. It improves high frequency reception in the 1.8, 2.4, 3.5, and 5 -5.8 GHz bands (for wireless computer WLANs and surveillance installations) as well as improves measurement of cell phones, wireless phones and high frequency data links. It is ideal for the general detection of covert cameras and bugs (where a high sensitivity is required) and also provides a directional indication of the transmitter’s location
OMNI DIRECTIONAL ANTENNAS
The straight and right-angle-bent screw-on dipole antennas are used for general signal enhancement. They are most sensitive along the side of the antenna and less sensitive at either end. The shorter antennas are particularly applicable for 5 - 6 GHz use whereas the longer antennas are best for 1.8 - 6.4 GHz applications. Most computer wireless devices are used in the 2.4 GHz band, but 802.11a devices are used in the 5 - 6 GHz range.
POLARITY OF SIGNALS
The polarity of a signal source is usually in a horizontal or vertical direction. This corresponds to the orientation of the strongest signal vector. The Zap Checker meters will register the highest measurements when the polarity of their external antennas match the polarity of the transmitted signal.
The polarity of the straight dipole antennas is along the long axis of the antenna. A vertically polarized signal would best be detected by a bent screw-on antenna in a vertical position. Rotating the antenna to a horizontal position will optimize the signal measurement for horizontally polarized signals.
The flat surface of the Log Periodic triangular antenna corresponds to the plane of its polarity. The microwave connection-cable on the Log Periodic antenna can be carefully bent to orient the antenna to either a vertical or horizontal polarization. The cable will break after 2 or more bends. We find most signals to be vertically polarized.
The Yagi antenna is polarized in the direction of its elements. A Zap Checker product mounted on a Yagi antenna will have a horizontal polarization when the antenna is held with the meter facing upwards. By turning the antenna so that the elements are aligned vertically, the RF signal measurements are enhanced for vertically polarized signals.
BAND SPECIFIC FREQUENCY FILTERS
The external SMA connectors of the models ZC 300 and ABC 126 can be used in conjunction with special band-select filters. These filters are placed in series between the meter and a detecting antenna. The filters are available for specific bands above or below select frequencies. The filters greatly decrease the strength of received signals at frequencies outside their specific passbands. Thus they focus the high sensitivity of the Zap Checker meters to a chosen frequency band. In this manner, the Zap Checker products can be customized to a number of selected frequency bands.
By using a variety of low cost connection adapters, i.e., BNC or TNC connectors attached to male-SMA connectors, most antennas and cables can be adapted to connect to the Zap Checker meters. These adapters are readily available through amateur radio stores (such as Ham Radio Outlet or Amateur Electronic Supply) or by catalog order through Allied, DigiKey, Jameco or Mouser.
The Zap Checker products are time saving, effective tools to use for detecting, installing and maintaining wireless RF signal links.
