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Wireless Video Basics 101
With our years of experience with Wireless Video Camera systems we can create solutions where others have failed.
FM Analog 2.4GHz and 5.8GHz Thank you for checking us out, we hope to give you a crash course education here to help you better understand the basics of video transmission in the microwave bands. This is a quick education to help you get started, please feel free to call us anytime if you have any questions or require additional information.
Ground Based, Point to Point, Fixed Transmitter and Receiver Location: We first start off with the understanding that we are transmitting video and audio on 2.4GHz and 5.8GHz band. The most common system used is FM Analog which can transmit and receive up to 525 lines of resolution which is a industry standard. The transmitter RF output power varies from 50mV at 3 Meter Range to 1-WATT based on the ratings, FCC Part 15, FCC Part 97, and FCC Part 90 approvals for different types of application such as License Free for all types of usage to Hobby, non commercial, to Business and Law Enforcement. The normal video and audio input and output signal is rated at 1 volt peak to peak again an industry standard. The transmitter is the part the video and audio inputs are connected to transmit the video and audio signal wirelessly to the receiver which receives the video and audio and connects to a TV, DVR or VCR type of devise to view or record. The higher the frequencies, 2.4GHz and 5.8GHz gives us more band width to transmit higher lines of resolution and the video looks more like broadcast quality you would except from your TV. The transmitter transmits the signal one way on a preset channel (frequency) and performs its best when we have a direct line of site between the transmitter and receiver. We need to make sure we have control of the 2.4GHz or 5.8GHz band with-in 50 to 75 foot radius around the receiver which receives the signal. The items we need to be concerned about are 2.4GHz and 5.8GHz home version wireless telephone systems. These wireless phones normally operate with spread spectrum technology which means when it is powered up, both ends, base station and hand set they continuously hunt for clear channels and frequency hop up and down the band. This will create white lines our video picture and sometimes popping noise in the audio. In cases with apartments, condos, and shopping malls we can not control the 2.4GHz or 5.8GHz band so systems with directional antennas and/or Spread-Spectrum or C-OFDM systems will give the best results. With a single dwelling home we can control the frequency and choose one band over the other if there are wireless phone system already in the home. If you have a wireless computer network in most all cases it will be an 802.11G system which is on 2.4GHz and locked onto a single channel, generally this does not cause any interference and the channel can be changed if it conflicts with the video frequency. We can transmit through plastic and glass as if it was not there, when we transmit through normally constructed walls, dry wall, wood, and insulation, the wall will trap a small amount of moisture which will attenuate the transmitted signal a little bit, the more walls the more signal loss. To over come this we need to either increase the transmitter power or add a higher gain receiver antenna to pick up the weaker signal. Red brick is made of clay which is earth, we can not transmit through earth, concrete is made with rocks and the rocks have iron which can block the signal. Concrete is sometimes unpredictable in that if we test out the wall we might find a gap in the mix which has less rocks and we have a stronger signal passage, good luck hunting. The ranges we rate our equipment is based under ideal conditions which is defined as in the desert with low to no humidity with the transmitter and receiver off the ground about 10 to 20 feet at a 300 foot and higher for longer ranges. The long range transmitter and receivers are effected by what we refer to as "Ground Effect" the greater the distance we transmit the great the height off the ground. When we transmit 15, 20, 30, or 40 miles remember the earth is round so for a 40 mile range you should plan having the transmitter and receivers about 60 to 80 above the ground. Another factor is salty air; if you are anywhere near the beach the salty air will reduce the range by 1/4 to 1/3 of the rated distance. In all cases we want to use a system that is rated a greater amount than the actual distance. If you measure out 800 foot distance between the transmitter and receiver we would recommend a1300 foot, you want to plan for less than ideal condition so that if or when the weather changes we are covered.
Moving Transmitter: When we transmit inside a building and walking around we are subjected to RF reflections, this is when the metal objects inside the building reflect the transmitted signal back to the receiver causing the receiver to receive more than the original signal and the picture flickers / blinks. To understand better how this works think of the transmitter signal like a light bulb and all of the metal inside the build are mirrors reflecting the light back to your eyes (receiver). As you can imagine you would have a difficult time locating the original source of the light. If we were to take this outside in the open we would have no problems, everything would work fine. Transmitting inside a build can be accomplished using a C-OFDM system which we will talk about near the end of this lessons.
Airborne Video Downlinks: This is mostly done by RC hobbyist that transmit live video and audio from a radio controlled aircraft to the ground to either fly from or record to relive the experience. Many companies that are involved with UAV's (Unmanned Aerial Vehicles) and AP (Aerial Photography) use wireless video downlinks to view the video to fly from a or view what the on board video recorder or digital camera is recording, the range can be from 1-1/2 mile to 25 miles. With the transmitter in the open sky's and the receiver antenna facing the transmitter we have a clear view and can travel many miles. The amount of RF output power from the transmitter and the type of receiver antenna will determined what the range will be. When we have a low gain receiver antenna such as 3dB patch the antenna beam width will be greater about 160 degrees, When we increase the gain of receiver antenna to 24dB we now have a antenna beam width of about 7 degrees. When you are flying out 5 to 25 miles the tracking is not difficult since the aircraft is normally flying in one direction and the 7 degree beam width opens up the further out the aircraft is.
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Digital / Ethernet / IP Cameras / Encoder - Decoder 5.3-5.8GHz OFDM - Orthogonal Frequency Division Multiplexing: OFDM - Orthogonal Frequency Division Multiplexing is a technology that transmits multiple signals simultaneously over a single transmission path on a single channel. Each signal travels within its own unique frequency range, carrier, which is modulated by the video, data. The spread spectrum technique distributes the data over a large number of carriers that are spaced apart at precise frequencies. This spacing provides the "orthogonal" in this technique which prevents the demodulators from seeing frequencies other than their own. The benefits of OFDM are high spectral efficiency, resiliency to RF interference, and lower multi-path or reflection, distortion.
5.8GHz C-OFDM Digital MPEG, MPEG 2, MPEG 4 & H.264 Indoor & Moving Transmitter C-OFDM Digital Video
C-OFDM - Coded Orthogonal Frequency Division Multiplexed transmission technology provides a superior means of transmitting wireless information in high multipath environments. C-OFDM systems use 2000 coded carriers within the main signal; each carrier is coded modulated for signal robustness. The loss of one or many coded carriers have no impact on the video received. Adjustable guard intervals minimize multipath interference. The system also uses Forward Error Correction coding, further increasing signal reliability. Multipathed signals are summed at the receiver, actually aiding in signal quality. C-OFDM systems have become the standard for transmission in Europe. C-OFDM transmitters involves three major components: A signal encoder, a modulator, and an RF transmitter. MPEG, MPEG 2, MPEG 4 & H.264 are the industry standards for encoding an NTSC or PAL signal, the modulation scheme is C-OFDM.
Wireless Video Installation Basics 101
Always perform a site survey to make sure you have Clear-Line-of-Sight with no obstructions between the Transmitter and the Receiver. Always mount the Transmitter and Receiver at least 10 feet higher than any obstruction. Always aim the Transmitter antenna enclosure Directly at the Receiver antenna enclosure. When using multiple systems in the same area, Always install all even channel Receivers 25 to 50 feet from odd channel Receivers. This will eliminate the chance of interference.
Contact Wireless Video Cameras.com Technical Support if you have any questions.
Wireless Video Installation Basics 101 Examples The below installation diagrams should be used to help you plan your wireless system installation carefully for the best results possible.
The above installation image illustrates that it is important to mount your wireless transmitter & receiver on poles to raise them above any obstructions. Besides raising them, it is equally important to make sure that there is a direct line of sight between them.
Fresnel Zone & Long Range Wireless Video Basics
Fresnel Zone Example
Fresnel Zone Clearance and Antenna Height CalculatorRadio Line-of-sightAt UHF and microwave frequencies, when you deploy an RF link between two distant sites you need to make sure you have "line of sight" between the two antennas. But at these frequencies "line of sight" does not simply mean that from one site you can "see" the other. When your distance exceeds, say, 5 miles (8 Km), you need to take into account the following factors:
The figure below illustrates these concepts with an exaggerated representation of a long link. The following sections describe these effects.
Fresnel Zone Definition The Fresnel zone is a long ellipsoid that stretches between the two antennas. The first Fresnel zone is such that the difference between the direct path (AB in the figure below) and an indirect path that touches a single point on the border of the Fresnel zone (ACB) is half the wavelength.
If a significant portion of the Fresnel zone is obstructed the receive-signal-strength at the receiving antenna can be greatly attenuated. A rule of thumb is that you need at least 60% of the first Fresnel zone clear of any obstructions in order for the radio wave propagation to behave as if it is in "free space". "60% of the first Fresnel zone" means a narrower ellipsoid with a radius that is 60% of the radius of this first Fresnel zone.
Even though at 2.4 GHz half of the wavelength is only 2.4 inches (6.2 cm), at long distances the radius of this ellipsoid can be quite large. For example, with a link distance of 31 miles (50 Km) the radius of this (60%) ellipsoid at the mid-point is 77 ft (23 meters). You can use the calculator to compute this radius at any point in between the two antennas. You may also change the percent value of the first Fresnel zone you wish to clear. Atmospheric RefractionUnder normal atmospheric conditions radio waves do not propagate in a straight line, they actually bend slightly downward. This is due to "refraction" in the atmosphere which affects radio waves propagating horizontally. To take this downward bending into account, we perform all the path calculations using a larger value for the earth radius, such that we can then consider the radio waves as propagating in a straight line. Equal Antenna Height SolutionFor any given distance the Fresnel zone calculator displays the antenna heights (same at both ends) such that the Fresnel zone just clears the earth surface as shown in the figure below.
Different antenna heights It is unusual that you would have both antennas at the same height, so the calculator lets you enter different heights for the two end points (all heights are above sea-level; see "h1" and "h2" in the figure at the top). Clearing an obstructionThe calculator allows you to quickly determine whether you have enough clearance above a particular obstruction in the RF path, or alternatively, how high you need to elevate your antennas to clear the obstruction. For each potential obstruction in the path you need to know its distance from one of your end points and the height of the obstruction above sea-level. Drawing the path in "Google Earth " is a quick way of identifying buildings or structures that lay in the direct path and finding their distance from the end points. You may need to use a topographic map, draw the line between the end points, and create an accurate terrain profile. If there are buildings or trees in the path you need to determine or estimate their height above the ground, and add it to the terrain elevation at those points. For each of these potential obstruction points, enter its distance from site 1 and the height of the obstruction above sea level in the bottom left input "spinners" of the calculator. On the right hand side the calculator displays the vertical separation between the top of the obstruction and the bottom of the Fresnel Zone. If this value is negative you can use the antenna height spinners to increase the height of one or both antennas until that clearance becomes greater than zero. Fresnel Zone Examples
Repeater Systems to Achieve Clear-Line-of-Sight Repeater Systems using multiple Wireless Video Transmitters & Receivers may be used to achieve Clear-Line-of-Sight to enable use when obstructions are in the way. RX 1 TX 2
TX 1 (camera) RX 2 (monitor or DVR) Note : Transmitter (TX 1) connects to the camera and sends the signal to Receiver (RX 1). These 2 units will be set on Channel 1. The video output from RX 1 will connect to the video input of TX 2. TX 2 will send its video signal to RX 2. RX 2 connects to a monitor or DVR. These 2 units (TX 2 & RX 2) will be set on Channel 3.
Antenna Towers to Achieve Clear-Line-of-Sight
Air-Craft Grade Aluminum Antenna Towers are the perfect low-cost solution to get above most obstructions to achieve Clear-Line-of-Sight. Light-weight, easy to install and come in 10ft. sections Purchase directly from: PALCO ELECTRONICS Universal Antenna Towers
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