Shure BG 3.1 Service Manual download pdf (Page 6)

Shure T2 Vocal Artist Microphone Transmitter

Characteristics

25C1018 (CC)

circuit (L203 and C213) capacitively coupled to a low-pass filter (C219,

L206, and C218). C213 and C219 provide a capacitively tapped voltage

divider for matching into the low-pass filter.

Final Output (ETSI-Approved Models)

Transmitter: This can deliver up to +11.5 dBm (14 milliwatts) to the

antenna. No user adjustments permit this value to be exceeded. Test-

point TP6 provides a termination point for the 50 Ω output. C243 and

L211 act as a series resonating network for the battery, which acts as the

antenna. The unit should be powered exclusively by a 9 Vdc dry battery

(an alkaline type like the Duracell MN1604 is recommended).

Voltage Measurements: With 9 Vdc applied to the unit, the fol-

lowing voltages should appear at the terminals of the output transistor:

S Vc = 8.83 Vdc

S Vb = .097 Vdc

S Ve = .32 Vdc

S Base current = 0.27 µAdc

S Emitter current =9.67 mAdc

S Collector current = 9.67 mAdc

S Power input = 87 mW

The output power is +9.5 dBm (8.9 mW) into a 50 Ω load, at a fre-

quency of 169.4445 MHz. At the lowest acceptable battery voltage of

6 Vdc, the final collector current drops to 8.84 mAdc and the output

power to +7.3 dBm (5.4 mW).

Spurious Emissions: To minimize the production and radiation of

spurious emissions and harmonic energy, and to promote stable opera-

tion, the collector of each RF stage is separately decoupled from the 9 V

supply by ferrite chokes, resistors, and bypass capacitors. The base cir-

cuits are similarly decoupled except they use resistor-capacitor (R-C)

networks, whose higher-impedance levels are more appropriate.

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Shure BG 3.1 Service Manual Page 6