22
Measurements
Connecting antennas:
Observe the utmost care when connecting antennas via cables , as these
cables can be connected to transmitters and/or power sources! Make sure
you have chosen the antenna you intend to test!! Connection to transmitters
and/or other sources can destroy the instrument or cause hazardous electri-
cal conditions.
When connecting to the “N” female connector on the instrument make sure
you are using either “N” male antenna or cable connector.
If antenna or cable is fitted with another type of connector use appropriate
adapter. Please observe that the use of adapters and cable connections of
poor quality may influence the SWR and give higher readings than the actu-
al antenna SWR. Once the antenna has been connected to the instrument
you switch the SWR True on and select the relevant frequency band by
using the Fc and FΔ. By sweeping the frequencies of interest while observ-
ing the graphs on the screen you should see VSWR or Return Loss curve.
Antennas are usually designed to have a SWR below a given value within
the band for which it is designed. As an example a GSM 900 antenna could
have the following specifications: Range 890 - 960 MHz SWR less than
2.0:1 typical 1.5:1.
Nearby objects
When testing SWR on low gain antennas (Gain <3 dBd) the influence from
nearby objects is small when the objects are more than ½λ away (15 cm at
GSM900). When testing high gain antennas ( e.g. Yagi’s and panel’s) you
should avoid objects in the direction of radiation.
Strong RF fields
When testing SWR on antennas located in strong RF fields, the reading you
will get on the SWR meter may be incorrect, because the strong RF field
present will be indicated as reflected power coming from the antenna. If a
precise reading is needed, you must switch off the disturbing source of RF
or move the antenna under test out of the RF field.
Bandwidth
Some antennas may need tuning by adjusting the length of an element or
by other means in order to cover the entire band of interest, please refer to
