Shure T2 Service Manual page 5

Shure T2 Vocal Artist Microphone Transmitter
Section:
RF ETSI
Characteristics
The output power is +16.5 dBm (44.7 mW) into a 50 Ω load, at a fre-
quency of 169.4445
MH
6 Vdc, the final collector current drops to 15 mAdc and the output power
to +13.9 dBm (24.4 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
supply by ferrite chokes, resistors, and bypass capacitors. The base cir-
cuits are similarly decoupled except they use resistor-capacitor (
networks, whose higher-impedance levels are more appropriate.
-Approved Models
Audio Input: Processed audio enters R201, an internal potentiom-
eter that is adjusted for 15 kHz deviation (100% modulation) when the
audio section provides a –2.2 dBV, 1 kHz tone.
Oscillation: The audio then goes to varactor diode D201, which is
part of the modulated oscillator-tripler stage (Q201). The latter's base-
emitter circuit operates as a crystal-controlled Colpitts oscillator in the
20 z region. Fundamental-mode crystal Y201 is tuned 10 kHz below
MH
series resonance by the series combination of frequency-netting coil
L201, diode D201, capacitor C203, and capacitor divider C206 and
C207.
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. C203, C206, and
C207 provide temperature compensation.
Tuned Circuits (
ETSI
Stage 1: The collector circuit of Q201 is tuned to the third harmonic
of the oscillator frequency (approximately 60
C210, L203, C214, C213, and C215. (The latter components also form a
capacitively tapped voltage divider for matching into the base of Q202.)
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: Q202 operates as a buffer, with the collector circuit tuned to
the output frequency (for example, 60
C245, C218, L205, C222, C221, and C224 perform tuning and imped-
ance-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: Q203 operates as a frequency tripler, with the collector cir-
cuit tuned to the output frequency (for example, 180
L206, C226, C227, C229, L207, C230, and C232 perform tuning and
impedance-matching.
Stage 4: Q204 operates as a tuned amplifier. Resistive loading on
the input provides stability. The output circuit consists of a resonant tank
z. At the lowest acceptable battery voltage of
stage is separately decoupled from the 9 V
RF
-Approved Models)
MH
z). In this case, L204, C216,
MH
4
)
R-C
z) by L202, C208, C244,
z). In this case,
MH
25C1018 (CC)