Sony DWM02/14 Product Information page 12

Technology
Simultaneous Multi-Channel Operation
With WiDIF-HP, the number of transmitters that can be used within the same band frequency is 1.5 times that of
an analog system, allowing for greater operability.
RF and third-order intermodulation
The RF related circuit design is an important aspect for realizing multi-channel operation. In wireless systems
with multiple channels, the intermodulation that is generated in the RF amplifier of the transmitter/receiver
often causes interference between the wireless channels. The RF block of an analog wireless system must be
designed carefully to deal with intermodulation. However, intermodulation cannot be eliminated completely,
either in an analog or digital system, as long as the RF part is composed of analog circuits.
CH1: 640.000 MHz
CH2: 640.500 MHz
Why are digital wireless systems advantageous to simultaneous multi-channel operation?
In an analog system, the D/U (Desired/Undesired) signal ratio will be the S/N ratio of the demodulated audio
signal. The higher the undesired signal level, the higher the noise will be in the modulated signal. Typically,
analog systems require a D/U signal ratio of 40 dB or more.
In the Sony digital wireless system on the other hand, an error does not occur provided the D/U signal ratio
is 20 dB or more. Therefore sound quality will not be impaired as long as this condition is met. The digital
wireless system provides interference rejection that surpasses conventional analog systems by 20 dB or more,
and is therefore much less prone to problems caused by intermodulation and is more efficient in handling
frequencies within a limited frequency range.
Application Example: Reality TV Show Production
Frequency environment: Clear channels are TV33, TV42, and TV55 only.
ANALOG
DIGITAL
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Key Features of WiDIF-HP
RF spectrum
CH 1 CH 2
Third-order intermodulation signals
Wireless channel cannot be allocated
due to the intermodulation noise
Frequency
TV33: 8ch, TV42: 8ch, TV55: 8ch
TV33 4ch TV55 2ch
TV33 4ch TV55 2ch
TV42 4ch TV55 2ch
TV42 4ch TV55 2ch
TV33: 12ch, TV42: 12ch, TV55: 12ch
TV33 4ch TV55 2ch
TV33 4ch TV55 2ch
TV33 4ch TV55 2ch
TV42 4ch TV55 2ch
TV42 4ch TV55 2ch
TV42 4ch TV55 2ch
Third-order intermodulation signals will occur
at 639.500 MHz and 641.000 MHz
Frequency
CH 1
CH 1 & 3 CH 2 & 3 CH 1 & 2
Total 24 channels
4-camcorder system
Total 36 channels
6-camcorder system
CH 1 CH 2 CH 3 CH 4 CH 9 CH 10
...
CH 2 CH 3
CH 1 & 2
Intermodulation free
special channel allocation
CH 11 CH 12
Equally spaced easy
channel allocation