Antenna Configuration Explained
A line locator is a simple tool to detect electromagnetic fields. The receiver picks up an electrical induced charge when crossing through a moving electromagnetic field. The current being generated within the receiver indicates the presence of a signal. The stronger the signal, the greater the induced current.
As the receiver is moved horizontally through the electromagnetic field, current increases and decreases relative to that proximity. The amount of current the receiver picks up is communicated to the user through an audible tone and visual display. The source of that electromagnetic field can be from a transmitter, but not always. There are passive electromagnetic fields all around us. For example power lines, cathodically protected gas lines, radio stations signals; virtually every pipe and cable that has metal or continuity carries some electrical charge that creates a detectable magnetic field.
The earth itself is a strong magnetic field. With all the electrical noise around us it’s important to understand how we can translate what we hear and see what our locator is telling us.
The Radiodetection receiver is made up of 5 antennas. 1 hollow round core antenna in the middle surrounded by 4 ferrite core antennas.
Ferrite core is a type of magnetic core used for its properties of high magnetic permeability coupled with low electrical conductivity (which helps prevent cousin eddy currents). In short, they read all frequencies cleaner and concentrate the signal into a smaller pathway making the locator lighter and ergonomically sexy.
The center round antenna controls the compass on the screen of the receiver and it's always on the screen. However it can be shut-off by entering into your advanced menu system by giving your On/Off key a quick press.
This compass detects the position of the magnetic field, which should match the direction of your target line. If the target line starts to turn, the compass will direct you the way your current is headed.
For example, if you are locating gas or water service to the main, when you get close to the main you have two magnetic fields intersecting causing your compass to tilt. Your compass will magnetize the direction where more of your current is headed when you are directly over the T or the intersection of the two pipes. When your compass isn’t directly lined up with the field or confused by multiple signals your automated depth reading will not display. This is because your locator knows the field is not clean and therefore an accurate depth may not be possible.
The same goes for when you are on a multi line corridor. If your compass is attracted to some constructive current from a neighboring line it will tilt towards that line until your field is isolated again. This is a good indication of interference and the direction your locator is mis-locating. If the neighboring line contains destructive interference it will tilt away through your locate until you're back into a clean area again. This is a good indication your signal isn’t properly isolated.
The alignment of the aerial antenna is linked to the reaction of the response as it travels through the electromagnetic field. A circular magnetic field comes above ground in a wide semi-curved horizontal antenna formation. An aerial antenna laying in a horizontal direction will give a large peak response when perfectly aligned over the apex of the field. This is know as peak response. In contrast, a vertical antenna will Null out, or get no response when over the target line because it’s completely perpendicular to the magnetic field.
The benefit of the Peak antennas are they allow for a larger sample size of current and the user can determine the orientation of the signal. Horizontal antennas are the best choice for locating utility lines, which are also horizontal. They ignore any lines crossing perpendicularly against your locate, eliminating unwanted interference. They are also a good choice for locating near T’s and elbows because they won’t pick up the interference from the perpendicular magnetic field crossing your path. This gives you a much tighter locate at a turn.
Vertical antenna’s gives a NULL response when directly over the line because the field does not flow through the aerial antenna. When you move the ariel to the either side of the field the flow goes through the antenna and gives a response. The sharp “non” response of the vertical Ariel is easier to use than the flatter peak response to the horizontal antenna and gives the user Arrows telling them the direction of the line. However, it is vulnerable to interference and should not be used for locating except in areas with no interference. A vertical Ariel indicates line position but not its orientation, which makes for locating around elbows and T’s difficult.
The very bottom horizontal antenna is represented by a small hill icon. This is called single peak mode. In a peak response the bar graph and numbers are greatest when you’re direct over the strongest part of the magnetic field. A tide mark appears on the bar graph when the peak is reached making it easy to identify the location of the line.
Single peak mode is one of the most accurate antenna responses because it’s closest to the ground and to the center of your magnetic field. The only drawback is that using a single antenna creates a wider peak response making it less evident when you are directly over your target. The audio and visual response is wider. For a quicker audio and visual response the dual horizontal peak antenna are a good choice.
The dual peak mode is represented by a large hill icon. The dual peak mode also has a more acute and quick visual and audio response making it the preferred mode for experienced locators that use mostly audio to perform their locates. Dual antennas also allow for some fancy algorithms to be implemented by Radiodetection, which we will discuss in a moment.
Guidance mode is a dual vertical antenna, which is almost as accurate as dual peak. Gain control is automatic in Guidance mode, which makes this the easiest mode to become familiar with the Radiodetection unit. Guidance mode also takes advantage of twin aerials and also applys some fancy filtering and algorithms to provide very accurate locates. Guidance mode is a good choice to become familiar with the locator but once you do you’ll want to graduate to…