Operating instructions
OPERATING MANUAL 2945A
46882-311D 3-43
See Fig. 3-8 a, & d, Distortion level and signal to noise level measurements , on page 3-33. The
distortion bar chart is graduated in dB and is also displayed as a digital read-out above the bar
chart. The Rx test menu is recalled automatically after pressing this key.
SINAD
Selects SINAD as the measurement method. The modulation generator is set to 1 kHz. By
filtering the demodulated signal with a 1 kHz notch filter and comparing the result with the
unfiltered signal, the SINAD level is established using the formula:-
SINAD
= 20
1
2
log
V
V
dB
=
++
+
20 log
()
()
SND
ND
dB
See Fig. 3-8 a, b, & c. Distortion level and signal to noise level measurements , on page 3-33.
The distortion bar chart is graduated in dB and the SINAD level is displayed as a digital readout
above the bar chart. The Rx test menu is recalled automatically after pressing this key.
Dist’n
Selects distortion percentage as the measurement method. The modulation generator is set to
1 kHz. By filtering the demodulated signal with a 1 kHz notch filter and comparing the result
with the unfiltered signal, the distortion percentage level is established by the formula:-
Distortion
= 100
2
1
V
V
%
=
+
++
100
()
()
%
ND
SND
See Fig. 3-8 a, b, & c. Distortion level and signal to noise level measurements , on page 3-33.
The distortion bar chart is graduated in % and the distortion percentage level is displayed as a
digital readout above the bar chart. The RX TEST menu is recalled automatically after pressing
this key.
Making measurements
(Examples of receiver tests).
The procedure for making each of the tests listed in the receiver testing overview, above, follows.
Some of the tests may require separate operations and others will only require a reading to be
made.
Sensitivity
Receiver sensitivity is defined as the minimum RF level required at the antenna to produce an
intelligible output of the modulated information.
The problem with the above definition is that of defining ‘intelligible output’. As this is a
subjective decision, sensitivity specifications require certain parameters to be set down. The
nature of FM and phase transmissions makes sensitivity measurements less straightforward than
with AM transmissions. A sensitivity test on an AM receiver can be stated as ‘X watts audio
output from Y µV RF input at Z% modulation’.