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RF output once the battery drops below its usable voltage range or
if the voltage controlled oscillator is unable to lock to the reference
oscillator.
Channel Selection via the SIP
Switches
Programming the synthesizer takes place each time the PWT is
powered ON. This operation is automatically completed by the
microcontroller to enable the correct frequency for transmission.
The required data to program the synthesizer is translated from the
2 – 8-pin SIP switches (in the form of a channel selection) to the
necessary code for frequency setting. This operation takes place
only when the unit is powered ON. For the switch settings to take
effect, the unit must be powered OFF and then back ON.
The transmitter includes the channel selection in the data frame. The
receiver confirms that the channel number within the data frame
agrees with the actual channel being used. If the two do not agree,
the receiver will not display a waveform. The technical specification
indicates the correlation of the SIP switch settings with the desired
channel and bandwidth.
Invalid Channel
When reading the channel selection from the SIP switches, the
microcontroller performs a check for validity. On the condition that
the settings are invalid, the microcontroller disables the RF output,
preventing transmission on an unknown channel. During power ON,
the microcontroller reads and stores the SIP switch settings on
board. No further changes to the switches affect transmit in any
way, until the unit is powered OFF and then back ON. In the event of
a loss of frequency lock, the microcontroller reloads data stored
internally in FLASH memory and reprograms all devices. In the event
the programming of the synthesizer’s registers changes during
operation, the synthesizer will lose lock, at least temporarily. This
prompts the microcontroller to reset and reprogram the synthesizer.
The entire RF section will be powered down if the synthesizer fails to
lock when it is reprogrammed. To re-enable the RF output, the unit’s
power must be removed and reapplied.
SIP switch Settings for
Transmitter Type
The channel selection uses the lower four bits of SW2. The upper
four bits are used to indicate the transmitter type. This information is
included in the data frame such that the receiver can confirm the
transmitter type. If the transmitter type indicated within the data
frame disagrees with what the receiver expects, then the waveform
will not display. The transmitter does not use this information for any
other purpose.
Baseband Data Selection for
Modulation
There are two modes of modulation for the transmitter PCBA. The
normal operating condition is to modulate the RF carrier with the
data generated internally by the PWT. An additional mode allows
external data to be used to modulate the RF carrier. The external
data mode is only used for testing and manufacturing purposes and
is not required in the field. To enable the external modulation mode,
the
ExtMod
input must be driven. For the internal data to modulate
the RF carrier, there must be no connection made to the
ExtMod
input (or any line connected to it must be switched to high
impedance). The
ModOut
line can be used to probe the digital
baseband signal for testing purposes.
