DSP-599zx Audio Noise Reduction Filter
March 6, 1997 7-7
• An asterisk is displayed in the upper middle section of the display if the
incoming CTCSS signal exceeds the tone squelch threshold level. The
audio output is unmuted when the squelch is open.
• Press
[Tone]
again to stop generator and return to the autodetect mode
• Press
[Mode]
to exit Test Instrument mode. Press the middle knob to
escape back to the test function menu.
CTCSS Tone Squelch
The decoder has a detector that pulls a DSP-599zx output pin low when a
signal exceeds the threshold. This output may be used to trigger a tape re-
corder or other monitoring device.
CTCSS Tone Squelch Switch Output Jack and Pin
Numbers
What are CTCSS tones?
CTCSS tones are normally used in VHF/UHF systems to help reject annoy-
ing interfering signals on repeaters or to allow only desired signals to be
heard on direct radio links. A selected CTCSS tone mixes with the transmit
audio to modulate a transmitted signal. When a tone is present on a received
signal, a CTCSS tone decoder output opens the receiver audio squelch, al-
lowing the incoming signal to be heard. The tone frequencies are all below
255 Hz and are usually not audible on most VHF/UHF radios if the frequen-
cy deviation is set correctly. The tones usually sound like a “hum” if they
can be heard.
CTCSS is an acronym for “Continuous Tone Coded Sub-audible Squelch."
32 of the tone frequencies are TIA (formerly EIA) standards. Some compa-
nies have trademarked names for their CTCSS tone systems and have ex-
Frequency -
Hz
Amplitude -
Millivolts rms Squelch Output
Decode
Input
67.0 - 254.1
see Tone Freq.
Table
5 - 2000 low = tone present
Encode
Output
67.0 - 254.1
see Tone Freq.
Table
5 - 500 NA
Channel
DIN Jack on
DSP-599zx
Output
Pin No.
Ground
Pin No.
A
“Radio A” 4 2
B
“Radio B” 4 2
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