Shure T2 Vocal Artist Microphone Transmitter
3
Characteristics
25C1018 (CC)
20 MHz region. Fundamental-mode crystal Y201 is tuned 10 kHz below
series resonance by the series combination of frequency-netting coil
L209, diode D201, capacitor C214, and capacitor divider C224 and
C230.
Frequency and Temperature Stability: To ensure frequency sta-
bility despite changes in the battery voltage, regulated 5 Vdc bias is ap-
plied to the varactor diode and to the base of Q201. C224, C230, and
C214 provide temperature compensation.
Tuned Circuits (FCC-Approved Models)
Stage 1: The collector circuit of Q201 is tuned to the third harmonic
of the oscillator frequency (approximately 60 MHz) by L205, C225, C234,
L202, C217, C237, and C233. (The latter components also form a ca-
pacitively tapped voltage divider for matching into the base of Q203.)
The output is double-tuned to provide high spectral purity. Regulated dc
bias is again employed to minimize changes in loading on the oscillator
stage and to stabilize the drive levels.
Stage 2: Q203 operates as a frequency tripler, with the collector cir-
cuit tuned to the output frequency (for example, 180 MHz). In this case,
L204, C216, C238, C236, L210, C235, and C222 perform tuning and
impedance-matching functions. As in the preceding stage, regulated dc
bias is applied to the base circuit to stabilize the drive level, and the
output is double-tuned to provide spectral purity.
Stage 3: Q204 operates as a tuned amplifier. Resistive loading on
the input provides stability. The output circuit consists of a resonant tank
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 (FCC-Approved Models)
Transmitter: This can deliver up to +17 dBm (50 milliwatts) to the
antenna. No user adjustments permit this value to be exceeded. Test-
point I110 provides a termination point for the 50 Ω output. C211 and
L207 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 = 8.88 Vdc
S Vb = .450 Vdc
S Ve = .473 Vdc
S Base current = 0.29 mAdc
S Emitter current = 21.5 mAdc
S Collector current = 21.8 mAdc
S Power input = 183 mW
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