FAQ'S

1. Antenna beam width and height- how is this determined and how should one choose this? Comparing to the antennas we purchase from Bluewave how do they fit into this overall scheme?

An antenna plot is like a road map. It tells you where the radiation is concentrated. Patterns are usually referenced to the outer edge of the plot which is the maximum gain of the antenna. This makes it easy to determine other important antenna characteristics directly from the plot.

Most antenna users are interested in the directivity or beamwidth of the antenna. This is usually referred to as the "half-power" or 3 dB beamwidth, the points between which half the power is radiated or concentrated, and specified in degrees. As an example, the typical half-power beamwidths of a 3, 6 and 10 element Yagi are 60, 40 and 30 degrees respectively.

Beam width is a function of design, which has to incorporate all the relevant (and related!) factors to achieve the optimal result: gain, VSWR ( voltage standing wave ratio), front-to-back ratio, operating frequency, & bandwidth. Bluewave antennas have excellent operating characteristics in that they are broadbanded, have a VSWR of 1.5:1 or less, a high front-to-back, and very consistent gain across the operating frequency.

If you require more coverage, choose an antenna with more beamwidth. However, more beamwidth can imply a lower nominal gain at the same frequency than an antenna with a narrow beamwidth. Beam width is related to gain-see below.

2. How is gain determined and why are the antennas we use the gain that they are?

What kind of radiation pattern is desired?
This is the first major delineator of antenna selection. The only way to increase gain is to concentrate power in a narrower beamwidth. The narrower the beamwidth, the greater the gain of the antenna.

To get a handle on gain, let’s talk about it in terms of using a Maglite flashlight. When you first rotate the bezel to turn it on, the light beam is diffuse (wide beamwidth) and the light intensity is not very bright (low gain). As you continue to rotate the bezel, the light beam narrows (decreasing beamwidth) and the light intensity becomes brighter (higher gain). By the time that you reach the end, the light beam is very tight ( narrow beamwidth) and the light is almost a pinpoint (highest gain). At no time did we (i) change the light bulb or (ii) increase the battery power. We have merely concentrated the same power in a more focused manner.

A Yagi antenna is basically a standard half-wavelength antenna with additional elements placed in front of it to focus the energy for transmission in one direction. The more directive elements, the narrower the beamwidth and the greater the gain. In other words, gain is simply how you focus the radiated energy at the transmitter and how you focus the ‘ear’ of the receiver.

Above 300 MHz, a 3 element yagi will typically have 6 to 6.5 dBd gain, depending on the physical size of the elements, the boom, and other design characteristics. Adding additional elements will increase the gain. (Adding 3.5 dB is DOUBLING the gain.) So the 10 dBd yagi has twice the gain of the 6.5 dB yagi.

A properly designed Yagi antenna increases in gain as the length of the boom is increased along with additional elements. This table will give some rough guidelines as to the gain, boom length and number of elements required.

*Wavelength (in inches) = 11803/F (MHz). At 900 MHz, 1.0 Wavelength = 13.114"

3. Omni-directional antennas- how is gain determined and actually affected since they do not have elements that can be added.

Omni antennas radiate transmit power (the signal) in all directions (360 degrees) and listen for incoming messages from all directions. Omni antennas, therefore, do not send a signal as far as a yagi antenna of the same gain.

A vertical omni directional antenna is often used for line-of-sight communications with mobile stations spread out in various directions usually restricted to the horizon. If greater performance is required, the antenna gain can be increased by using a collinear type of omni that decreases the vertical beamwidth and hence concentrates more power on the horizon where it will be most beneficial. Increasing the length of the antenna ( adding vertical elements) will increase the gain of an omni antenna.

4. Mounting requirements- how is wind load determined and how are the mountings designed for proper attachment?

WIND LOAD = 1/2 X AIR DENSITY X (WIND VELOCITY SQUARED) X (CROSS SECTIONAL AREA)

If the antenna is attached to a tower or mast, what is the diameter of the pipe or mast? Will the antenna be rear or center mounted?

For an exterior mount, the integral strength of the design must be considered such as its ability to withstand wind, ice, heat/cold and other extremes. You should also assess the ability of the major components such as the feed, a radome if so equipped, and connectors to withstand stress. The materials and hardware used in the construction of the antenna are also important. Outside mounted antennas should use durable materials such as aluminum with heavy duty hardware. Additionally, has the antenna been designed to properly operate with 1/2" of radial ice encrusting on it, or will it stop working until the ice melts?

All Bluewave antenna mounts are designed to support and hold still the antenna as designed, which includes that antenna under stress (radial ice).

5. Grounding of antennas for noise reduction and system protection. Are there any other special grounding requirements or practices that should be taken into account for proper antenna grounding?

It is important to point out at the start that lightning protection is primarily a function of how much time and money you are willing to spend. Obviously, the more expensive the radio and the importance of system connectivity, the more robust your protection should be.

Lightning protection must be examined from four distinct directions. First off, the place where the antenna is mounted (such as on a tower) is important. Then there must be input protection from the lightning strike itself, typically in the form of a huge and rapid build up of voltage and current at the input to the radio. Thirdly, a proper ground system must be employed to rapidly conduct the lightning bolt energy away from the radio. Finally, protection is required at the output or main power supply such as the line voltage supply (e.g. the 115 VAC we obtain from a line cord).

If at all possible, don't mount your antenna on the highest building or tower. Place it a few feet lower and hopefully the fickle lightning bolt, if it generates a direct hit, will not discharge through the antenna. Furthermore, the boom or mast should be grounded to the mast or tower. Don't forget to ground guy wires that are used on stabilize towers. They are just as likely to be hit since they extend over a wide area around the tower.

The most important lightning protection is a good low impedance Earth/ground connection to the associated equipment. The Earth ground connection should be a copper plated rod preferably at least 5-8 feet in length driven into the ground. This ground rod should be located as close to the equipment as possible, typically just outside of a building at the entry point of the antenna feed-lines.

6. Using propagation patterns how is distance of propagation determined and how are the propagation patterns of an antenna determined? This is required to assist the customer in determining which antenna, gain and pattern to choose for his application.

Typically, propagation software is employed to determine appropriate antenna gain and mounting height. This software will incorporate such data as surrounding terrain, operating frequency, antenna beamwidth, antenna gain, overall system gain and other related factors. This is a service that many design firms specialize in.

7. Do antennas meet Class 1, Div. 2 applications?
As we understand it, there are no antennas that are rated as a Class I, Div. 2 capable device. Antennas are not classed as electrical equipment and are therefore not included as a component for this specification.
However, Bluewave antennas generally meet the criteria for Class I, Div. 2 if this standard were to be applied. For instance, the antennas do not spark or arc in normal operation. There are in fact, no active components in the antenna. Secondly, the antennas have no operating temperature. They operate in ambient air temperatures which are not likely to exceed 100 degrees Centigrade. Finally, since the antenna does not operate as “electrical equipment” it has no particular “safe failure mode of operation”. The antenna is generally inert electrically.

8. Does the BW900001 surge protector meet Class 1, Div. 2 applications?
Here are the facts on the BW900001 and similar products, relative to Class I, Div. 2 applications. All comments assume that the device is properly installed with a low impedance path to ground from the bulkhead connection. There are two modes: normal operation; and operation during a lightning surge event.

There are three basic criteria that the component must meet:

1. No arcs or sparks in normal operation.

The BW900001 Lightning Protector (LP) is a passive device, consisting of a gas tube to ground for purposes of diverting the surge current, and a blocking capacitor to keep any voltage spikes from reaching the equipment. The gas tube is a sealed device. No electrical arc or spark generation will occur during normal operation. Properly installed and grounded, the device can handle a lightning surge up to 20kA, 8/20 uSec waveform, without generating an external spark or arc.

2. Components and Device enclosure must stay below 100 degrees Centigrade.

When operated within the RF Power limits stated in the specification, the internal component and case temperature is below 100 degrees Centigrade. This applies for both normal and surge event operation.

3. Safe failure mode for electrical equipment.

The normal failure modes for this LP are an open or shorted coupling device, or a shorted gas tube. In either event, the system will cease functioning properly, requiring replacement of the device. These failures will neither create arcs or sparks under normal operation or a surge event, nor cause excessive heating. It is statistically possible for a Gas Tube to fail in the open condition, although it is rare. If this occurs AND a lightning event occurs, arcing is possible within the device.

The BW900001 is not a weatherized unit, and is not certified by a Nationally Recognized Test Laboratory (NRTL) as a Class I, Div 2 capable device. Under normal operating conditions, even with an internal component failure, neither arcing nor high temperatures should occur. During a Lightning strike, internal arcing is possible if the voltage rise time is extremely fast or the surge current is extremely high. If the device is within another enclosure (NEMA 12 or 13 have been mentioned), the probability of igniting flammable gases or vapors is also significantly reduced.

Warranty

Cables & Connectors
1. All products sold with integral cable feeds are electronically tested to ensure they meet specifications. Accordingly, cracked or damaged cables in the field are not considered valid warranty returns.

2. All factory applied connectors are pull tested to ensure physical and electrical integrity. However, field installation conditions can sometimes put tremendous strain on cable and connectors. Connectors that may fail under these circumstances are not considered valid warranty returns. Bluewave representatives will work with you to supply replacement components.

Horizontal Polarization Mounting in Wet Environments
1. Antennas that are known to be mounted using horizontal polarization in wet or coastal environments should be ordered without the Dipole vent hole.

2. If any standard vented dipoles are installed for horizontal polarization in wet or coastal environments the vent hole should be sealed (as indicated in the installation instructions provided with each antenna).

3. Antenna failure resulting from a failure to seal the vent hole in these circumstances is not considered a valid warranty problem.

Anodizing

Is anodizing better than Alodine® or Iridite® finishes?

Yes. Chromate Conversion (aka Alodine® or Iridite®) is a chemical treatment process for Aluminum used to provide corrosion protection and surface preparation for paint and adhesives. Chromate is an excellent treatment method for paint or adhesives since it greatly enhances the product's ability to form a bond with the aluminum. It is frequently used on electrical and electronic equipment because it provides increased corrosion resistance while remaining electrically conductive. However, Alodine® or Iridite® processes are thin-film processes. The coatings are easily scratched, exposing the raw aluminum underneath to corrosive atmospheres. Anodizing, on the other hand, creates a chemically bonded coating that penetrates beyond the surface thereby providing a superior finish and an electrically stable structure.

Is anodizing necessary?

Raw aluminum exposed to most atmospheres will quickly degrade. Antennas that are not anodized, particularly those that are not fully welded, will change electrically as the aluminum breaks down. Corrosion will begin to cause intermodulation problems and eventually the antenna will fail.

Antennas that are coated with thin film processes (Alodine® or Iridite®) are susceptible to surface scratching – providing opportunities for corrosive degradation. These finishes are inferior to anodizing.

Copyright © 1996-2007 All rights reserved
Bluewave Antenna Systems Ltd.