9
July 6, 2010
AN1559.0
MTV Application Setup
The following setup should be used for testing QHx220
noise cancellation ability for a MTV application. It is
important to maintain the identical core setup used in the
“MTV Optimization Setup (Static Coupling Channel)”
section on page 7. Otherwise, the optimization values will
not be valid.
Begin with the aggressor source (signal generator) and
QHx220 board powered off. Turn on the MTV generator
and MTV tuner and record the receiver’s signal quality
parameters (C/N, BER, etc.) once a channel synch is
achieved. Find the weakest MTV generator level that will
still enable the tuner to maintain synchronization. Next,
set the aggressor signal generator to the same channel
frequency and set the power level to roughly 10dB above
the peak of the broadcast MTV signal. The aggressor
signal needs to be high enough to show degradation of
the receive signal strength reported by the MTV receiver.
Remember not to exceed ~ -45dBm at the input of the
QHx220. Once an aggressor power level is found that
degrades the receive signal strength reported by the MTV
receiver, turn on the QHx220 board and set the
optimized I and Q values that were determined in the
“MTV Optimization Setup (Static Coupling Channel)”
section on page 7. This should result in a <15dB
recovery of the receive signal strength power reported by
the MTV receiver if the board was optimized correctly.
However, since the setup was slightly modified from the
original optimization setup, it should be possible to fine
tune the QHx220 to improve the in-band noise
cancellation. Please note that any changes to the cable
lengths or slight impedance changes will slightly impact
the optimal gain and phase of the QHx220. Therefore, in
the MTV application setup, adjust the gain and/or phase
one step at a time and monitor the MTV receiver
sensitivity (or any other signal quality parameter (i.e.
C/N, BER, etc.). Continue to adjust the gain and phase
one step at a time until no further improvement to the
receiver sensitivity can be achieved.
FIGURE 9. MTV TESTING SETUP DIAGRAM
MTV
AGGRESSOR
PATH
MTV
GENERATOR
QHx220
MTV
TUNER
CANCELLATION
NODE
MTV RECEIVE PATH
POWER
SPLITTER
ATTENUATOR PAD
TO SET COUPLING LOSS
POWER
SPLITTER
AGGRESSOR
GENERATOR
Application Note 1559
