Chapter 10 2-Port Transmission Testing
86
CellAdvisor JD720C User's Manual
Introducing 2-port transmission measurements
The 2 Port Transmission measures the level of the signal attenuation of passive RF elements
such as cables and filters, or the level of gains of active RF elements such as amplifiers. The
frequency band to measure the characteristics of a cable must be calibrated before
performing the insertion loss/gain measurement.
Gain
The gain is the gain resulting from the insertion of a device in a transmission line, expressed
as the ratio of the signal power delivered to that part of the line following the device to the
signal power delivered to that same part before insertion.
Insertion loss
The insertion loss is the loss of the transmitted signal power resulting from the insertion of a
device in a transmission line. It is usually expressed relative to the signal power delivered to
that same part before insertion. In most systems, insertion loss is introduced by things such
as connectors, splitters, or couplers.
The insertion loss of a device (which may be a whole line) may also be referred to as
attenuation. Line terminations play an important part in the insertion loss because they reflect
some of the power. Apart from this, it is clear that not all of the power that is sent in to the line
at one end appears at the other. This is because of radiation losses, resistive losses in the
conductor as well as losses in the surrounding dielectric. The loss resulted from inserting a
transmission line between a source and a load is called the insertion loss of the line.
If the power transmitted by the source is PT and the power received by the load is PR, then
the insertion loss is given by PR divided by PT. For maximum power transfer the insertion
loss should be as small as possible. In other words, the ratio PR/PT should be as close to
one as possible, which in decibels means as close to 0 dB as possible.
Display screen
shows an example of 2 Port Transmission measurements.
