Working with Antennas

Antenna Development and Experimentation

Antenna experimentation and testing is one of the most common uses for the DIGI-FIELD. The DIGI-FIELD can regulary replace instruments costing thousands of dollars more with simplicity and portability. The operator can accurately record digital information for a variety of tasks. The source should be emitting an RF signal (CW or Pulse), and the DIGI-FIELD should be located in the same area as the antenna under test (AUT).
To simplify and understand antenna radiation patterns, please refer to the figures below. As with any field strength meter, the lower the SWR ratio, created by an efficient ground plane and antenna location, the better the efficiency of the antenna. Changes in SWR can be observed in the field strength.

The DIGI-FIELD was designed to be used with many antenna configurations. It can be located several wave lengths away and connected with 50 ohm coaxial cable. Coaxial attenuation should be taken into account when doing accurate measurements.

Antenna Patterns

The figure on the left represents a top view of a typical antenna pattern of a mobile antenna configuration. The image on the right is a side view of the same mobile installation. Many companies make sophisticated readings of gain (degrees of permormance) and shapes of patterns. Sophisticated calibrated receivers, computers, and antennas are used to obtain the horizontal/azimuthal plane pictures and vertical/elevation pictures. These are also measured with a rotating platform. With simple instructions, the DIGI-FIELD can measure with a high degree of accuracy.

Using the DIGI-FIELD for Antenna Patterns

To make an azimuthal (or top view) pattern, readings should be recorded on the DIGI-FIELD 360 degrees around the transmitting antenna. Start by sending an emitted power to the antenna at a level that will not saturate the DGF. Use enough power to control any possible external emission that can cause interference. (It is suggested to obtain a reading between 5.00 and 12.00). The distance selected from the DGF to the AUT for measurement will depend on power and frequency. The height of the DGF should be the same as the antenna under test (AUT). For the azimuthal data, a non-conductive tripod and a extended string can be used to keep the same radius around the antenna (360 degrees). Take measurements every 15 degrees. By using a temporary protractor around the base of the antenna (a paper template is useful) and knowing the frequency of the transmitted source, use the supplied curves (readings can be converted to dBm or dB's using the highest reading as 0 degrees) Plot in circular graph the corresponding difference of dB's at different angles of rotation. (see figure)
For the elevation Plane, radiation patterns must be measure vertically. The DIGI-FIELD will plot the angle of radiation. (see figure) Please note: the location and environment affect radiation patterns. Readings may vary slightly due to ground and nearby objects.
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