UNAOHM
NG500 (Rev. 0)
11
response of each instrument does not guarantee perfect linearity (they both have a certain
tolerance on linearity).
Furthermore, the display on the tube may appear poorly defined due to the nature of the “noise”
signal. To improve it, it may be useful to include a video filter if provided with the field strength
meter.
Once the reference level
dB(ref)
has been established
,
disconnect the cable and connect the
generator to the input of the device under test (DUT) and the FSM to the output of the DUT as
per figure 4A.
As a result, the loss (or gain) of the device will be determined by :
dB(loss) = dB(ref) - dB(measurement)
dB(gain) = dB(measurement) - dB(ref)
Warning: if the device under test is active with gain and wideband, be careful since the power
increase due to the extended bandwidth may easily cause overload (remember that each time the
bandwidth is doubled, corresponds to a 3 dB increase in signal level).
Therefore, if necessary, engage some attenuation on the generator until proportionality is
reached. In other words, if a 2 dB attenuation is inserted on the generator, a similar attenuation
should correspond on the measuring instrument too.
For selective devices (amplifiers, filters, etc.) it is also necessary to adjust the frequency
deviation of the spectrum analyser in order to display the response curve at its best.
