Antenna Selection Guide
Elsema has a wide selection of antennas manufactured by our RF engineers using the latest technology and test equipment from Rohde & Schwarz. We have our standard antennas on 915MHz, 433MHz, and 151MHz that are always in stock. Antennas come on different frequency bands, connectors or coaxial cables can be designed to meet specific customer requirements.
To select the correct antenna you will need to match the antenna frequency to the equipment you are using. Most of Elsema’s radio equipment is on 915MHz, 433MHz and 151MHz. For the higher frequencies such as 433MHz and 915MHz it is important that the coaxial cable is low loss and is terminated with a high quality connector.
As a general rule we have used high quality SMA connectors for frequencies above 300MHz. For frequencies below 300MHz the PL259 and the SO239 is used. We do not use the PL259 and the SO239 on frequencies above 300MHz as this connector does not work well above 300MHz. Other connectors available on special requests are N, BNC, MCX and MMCX.
Other considerations in selecting the correct antenna is the gain, SWR and coaxial cable. Antenna gain is often measured with respect to a hypothetical antenna that radiates equally in all directions, an isotropic radiator. This gain is in decibels called dBi. The antenna gain can also be measured in dBd which is equal to dBi -2.15.
The SWR is a measure, of the amount of mismatch between the load (Antenna) and the transmission lines impedance. A SWR of 1 is a perfect match which occurs on a transmission line where there are no reflections. An SWR less than 1.5:1 is considered good and a SWR greater than 2:1 is usually unacceptable. This may indicate a problem with the antenna. Refer to the table to convert SWR to power transmitted or reflected power.
All coaxial cables have attenuation. Using good quality coaxial will minimize the loss in the coaxial cable. Refer to the coaxial cable data table to compare common types of coaxial cables.