M850-00
T855 Initial Tuning & Adjustment
B3.7
Copyright TEL 31/09/98
3.4.6 CTCSS
3.4.6.1 Decoder Operation
Program a CTCSS tone on the set channel using PGM800Win.
Set the RF signal generator output to -70dBm.
Modulate the generator with:
• a 1kHz tone at ±3kHz deviation (±2.4kHz) [±1.5kHz]
• a CTCSS tone at the programmed frequency at ±500Hz deviation (±400Hz)
[±300Hz].
Check that the receiver gate opens and the front panel "Gate" LED is on.
3.4.6.2 Opening Sinad
Adjust RV230 (front panel gating sensitivity) fully clockwise.
Reduce the RF signal level to -110dBm.
Observe the sinad meter and reduce the RF level until the receiver mute closes.
Slowly increase the signal level until the receiver mute just opens and stays open.
With PL240 pins 1 & 2 linked (G - H; high pass filter bypassed), check that the
sinad is less than 6dB.
Reset RV230.
3.4.6.3 High Pass Filter
Set the audio processor links as follows:
Reset the RF signal generator output to -70dBm and note the line level (measure-
ment A).
Reduce the 1kHz generator to zero output and measure the line level again (meas-
urement B).
Check that measurement B is at least 30dB below measurement A.
Plug Link Function
PL210 1 - 2 A - B de-emphasised response
PL230 2 - 3 N - P audio from internal CTCSS speech filter
PL240 4 - 5 K - L audio input via PL230 or I/O pad
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