Tait TB7100, Service Manual

Page: 50 / 370

50 Circuit Descriptions TB7100 Service Manual
© Tait Electronics Limited October 2005
Speed-up
Techniques
To reduce the change-over time between transmit and receive, part-time
speed-up techniques have been implemented. Speed-up involves changing
some resistor values while simultaneously changing the PLL IC settings.
This process is implemented in hardware under software control in
conjunction with use of the synthesized reference input. The result is a
transmit-receive settling time of less than 4.5ms. (The switching time is
measured for a frequency change equal to the first IF plus 10MHz or 1MHz,
depending on the repeater offsets used for the band. This implies a
synthesizer transmit-receive change-over plus an offset of 1 MHz or 10 MHz
in less than 4.5ms. The ramp-up and ramp-down of the transmitter, which
totals 1ms, extends this change-over time to 5.5ms.)