Operating instructions

LOCAL OPERATION
3-46 46882-311D
Return to the RECEIVER TEST screen and adjust the RF output level to that required by the test
specification.
Switch the RF generator output
ON by pressing the orange [ON OFF] function key.
The audio output from the receiver is measured and the level and frequency displayed.
For measuring sensitivity levels, rather than checking against settings, the various parameters on
the monitor can be adjusted in steps using the LEVEL [
] and [ ] keys, or by precision
adjustment using the variable control.
AF bandwidth
The audio bandwidth of a receiver should be complementary to that of the transmitter or
transmitters associated with it.
The test for audio bandwidth is made by establishing a reference frequency, usually 1 kHz, and
reference level, then varying the modulating frequency until the measured audio output level
reduces by 3 dB. The 3 dB points above and below the reference frequency will be the limits of
the AF bandwidth.
When carrying out audio bandwidth tests the monitor audio filtering should be set to the widest
possible, i.e. 50 kHz.
Note that most FM transceivers apply pre-emphasis filtering to the transmitter modulation and
de-emphasis filtering to the demodulated signal.
AF distortion
The two methods used for quoting distortion within radio receivers are Distortion Factor and
SINAD.
SINAD tests are usually made in conjunction with sensitivity testing (see above), while distortion
test results are often quoted within the power output parameter. For example ‘3 Watts output
with better than 10% THD’ (total harmonic distortion).
The signal to noise level is also quoted but is a measure of receiver quality, not a true measure of
distortion.
The AF distortion measuring facility performs continuous reading and display metering using the
selected function, (SINAD or distortion factor). Therefore a distortion test can be carried out by
ensuring that the RF generator is tuned to the correct frequency, select the distortion measuring
function required and set the levels of the RF and AF generators. The distortion factor or SINAD
level is then read from the screen.
To obtain sets of readings relating to differing levels of RF or AF, the levels are reset and the new
reading made.