Analogue Tv: Measuring The Video / Audio Ratio (V/A) - Promax TV EXPLORER II User Manual

When at the RF input appear an important number of carriers with a high level the tuning
circuit may become out of control, giving as a result wrong level measurements. To be
able to determinate the equivalent level of a carrier group (with similar levels) at the RF
input, it is possible to use the expression:
L t =L + 10 log N
L t : equivalent total level
L: average level of the carriers group
N: number of carriers
So, if there are ten carriers with a level around 90 dBµV, their equivalent level will be:
90 dBµV + 10 log 10 = 100 dBµV
Observe that in this case, loss of tuning by overload of the RF input may occur besides
other effects such as tuner saturation and generation of intermodulation products that
may mask the spectrum visualization.

5.14.2 Analogue TV: Measuring the Video / Audio ratio (V/A)

In the Audio/Video measurement mode, on the screen appears the following
information:
FREQ:
CH:
In addition to the video carrier / audio carrier level ratio (16.2 dB in previous figure)
it also shows the frequency or channel, depending on the tuning mode selected, and the
Carrier/Noise ratio.
Page 50
0 10
168.25 MHz
S10
Figure 23.- Measurement of the video/audio ratio
USER'S MANUAL. TV EXPLORER II/II+
20 30
LEVEL: 78.2
C/N 40.1
» V/A: 16.2
FM DEV: - - -
WARNING
40
dBµV
dB
dB
kHz
09/2009