DB1065 Datasheet, PDF (8/23 Pages) CML Microcircuits – CTCSS Encoder / Decoder Development Kit

3.4.2 Transmit audio path verification
a. Using an audio signal generator, set for a 1KHz sine wave at 300 mVrms, connect the audio
signal generator to TXIN.
b. Connect an oscilloscope or audio analyzer to TXOUT.
c. Measure the output level and calculate the gain difference between TXIN and TXOUT.
20*log Vin/Vout where Vin = TXIN and Vout = TXOUT.
d. Calculate the level that represents -3 dB below the output level at TXOUT for a 1khz sine
wave.
3dB
10 ²⁰  TXOUT which equals .707 X TXOUT = -3dB level
e. Lower the frequency of the signal generator until the -3dB level is reached.
f. Measure the output frequency of the signal generator. This will be the lower -3dB band edge of
the TX audio filter.
g. Raise the frequency of the signal generator until the -3dB level is reached.
h. Measure the output frequency of the signal generator. This frequency will be the upper -3dB
band edge of the TX audio filter.
h. Remove ground from PTT . The 1KHz signal applied to TXIN should not be present at the
TXOUT connection.
3.4.3 CTCSS decoder verification
a. Remove ground from PTT .
b. Measure the logic level on the MONIT0R output. With no CTCSS tone it should be greater
than 3 volts dc.
c. Connect an audio signal generator to RXIN. Adjust the audio generator’s level to 50 mVrms
and its frequency to equal the CTCSS tone frequency (  1 hertz ) as set on the dip switch D0-D5
using Table 4: CTCSS Tones starting on page 17.
d. Measure the logic level on the MONIT0R output. It should be less than 1 volt dc when
detecting a CTCSS tone.
e. Connect CARRIER SENSE to +5VDC. MONIT0R output should go to a hi logic level
(>3VDC).
3.4.4 Receive audio path verification
a. Ensure PTT and PTL is not connected to ground.
b. Using an audio signal generator, set for a 1khz sine wave at 300 mVrms, connect the audio
signal generator to RXIN.
c. Connect an oscilloscope or audio analyzer to RXOUT.
d. Measure the output level and calculate the gain difference between RXIN and RXOUT.
20*log Vin/Vout where Vin = RXIN and Vout = RXOUT.
e. Calculate the level that represents -3 dB below the output level at RXOUT for a 1khz sine
wave.
3
10 ²⁰  RXOUT or .707 X RXOUT = -3dB level
f. Lower the frequency of the signal generator until the -3dB level is reached.
g. Measure the output frequency of the signal generator. This will be the lower -3dB band edge
of the RX audio filter.
h. Raise the frequency of the signal generator until -3dB level is reached.
i. Measure the output frequency of the signal generator. This will be the upper -3dB band edge of
the RX audio filter.
j. Connect ground to PTL. RX path audio should not be present at the RXOUT connection.
20480150.001 MX-COM
1996
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