June 15, 2005 6815854H01-A
4-12 Troubleshooting Procedures: UHF Range 1 (380–470 MHz) Band Main Board Troubleshooting
NOTE: The UHF band radios use high-side injection with an IF frequency of 109.65 MHz; therefore,
the receive VCO frequencies are 109.65 MHz higher than the selected radio channel
frequencies.
NOTE: If a failure is indicated in any of the VCOs, whose operation is defined in the table above, then
the respective circuit should be checked to ensure proper bias is being applied to the
transistor. Specifically, the transistor collector pin should be at 8.2 V and base-emitter voltage
should be on the order of 0.8 V. The steering line voltage should be in the range of 2 V for the
lower frequency end of operation, and on the order of 11V at the upper frequency end of
operation. There could be typically +/- 1 V deviation from the above quoted numbers, which
allow for tolerances in the components. A clean, steady, frequency spike should be observed
on a spectrum analyzer of typically -18 dBm at the end of the resistive pad in the collector
circuitry of a properly working VCO.
3. Continue troubleshooting by using the Fail 001 troubleshooting chart in Chapter 5.
Table 4-7. Test Mode Channels UHF Range 1 (AUX 4 is not used for VCO selection in UHF)
Test
Mode
AUX (TX Logic)
TX
VCO
TX Freq
(MHz)
AUX (RX Logic)
RX
VCO
RX Freq
(MHz)
RX VCO
Freq
(MHz)1 2 3 1 2 3
Chan 1
000
Q5825380.0250010Q5901380.0750489.7250
Chan 2
000
Q5825391.4750010Q5901391.4250501.0750
Chan 3
000
Q5825408.9750010Q5901408.9250518.5750
Chan 4
000
Q5825424.9375110Q5903424.9875534.6375
Chan 5
100
Q5826425.0250110Q5903425.0750534.7250
Chan 6
100
Q5826436.0250110Q5903436.0750545.7250
Chan 7
100
Q5826455.8750001Q5905455.8250565.4750
Chan 8
100
Q5826469.9375001Q5905469.9875579.5750
Table 4-8. VCO Frequency Calculation and Switching Logic (UHF Range 1)
VCO AUX1 AUX2 AUX3 VCO Frequency
RX VCO Q5901
010
489.65 <= f < 519.65
RX VCO Q5903
110
519.65 <= f < 549.65
RX VCO Q5905
001
549.65 <= f < 579.65
TX VCO Q5825
000
380 <= f < 425
TX VCO Q5826
100
425 <= f <= 470
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