Transmit Vco And Related Circuitry (Uhf Radios) - Tait TM9100 Service Manual

9.6

Transmit VCO and Related Circuitry (UHF Radios)

If there is no fault with the power supplies, the PLL inputs and output, and
Introduction
the loop filter, check the VCO and related circuitry. The procedures in this
section apply only to UHF radios with a system error or transmit fault, and
therefore with suspect transmit VCO and related circuitry. (The minimum
and maximum transmit frequencies for the different UHF frequency bands
are defined in
The measurement points for diagnosing faults in the VCO and related
circuitry are summarized in
Table 9.3 Minimum and maximum transmit frequencies for the different UHF frequency bands
Frequency band
H5
H6
TM9100 Service Manual
© Tait Electronics Limited August 2005
Table 9.3.) There are five aspects:
Task 23: check transmit VCO
Task 24: repair PLL feedback
Task 25: repair transmit VCO
Task 26: check switching to transmit mode
Task 27: check transmit buffer amplifier
Transmit frequency in MHz
Minimum
371 ± 5
419 ± 5
Figure 9.8.
Maximum
492 ± 5
545 ± 5
Frequency Synthesizer Fault Finding 201