The CircuitWerkes Subaudible Tone Decoder
Description
The CircuitWerkes Subaudible Tone Decoder provides a reliable and accurate solution for
decoding subaudible tones from satellite, automation, or other sources of audio. The unit has dry relay
contacts and an LED indicator for each of the standard three subaudible signals, 25HZ, 35Hz and the
Combination of 25HZ and 35Hz. Alternately, the Sub-03a may be ordered set for 50/75Hz tones.
The audio input can accept balanced or unbalanced audio at input levels of -20dBm to +8dBm.
The output is balanced transformerless and is easily capable of driving a 600 ohm load. Subaudible tones
are typically attenuated by 30dB at the audio output and it is short-circuit protected.
Installation & Setup
CONNECTIONS:
Connections to the Subaudible Tone decoder are fairly straight forward. Your audio passes through the
decoder via the Audio In and Audio Out jacks. The audio input jack has jumper J-3 associated with it. J-3
provides a convenient way to unground the input audio sleave if desired. When the input is unbalanced, the
(-) input lead must be tied to ground. Relay outputs and the power input are brought out to both barrier
strips and a Db-9 connector. Two additional barrier strip positions are for the relay disable function. The
Sub-03a must have a connection between these two positions for it to output contact closures. Finally, in
addition to the terminal and Db-9 locations, the power input may be also be made to a 2.5mm coaxial (or
"barrel") connector. All of three of the power connectors are in parallel with each other, so only one power
source at a time can be connected to the Sub-03a. See page 3 for connection details. Power is provided
by the included "wall-wart." Optionally, the decoder cam be powered with any supply of 18-24 Volts AC
or DC capable of delivering 150mA.
The relay outputs are dry N.O. contacts capable of switching loads up to 10 watts. We recommend slave
relays if you intend to switch heavy loads or high voltages.
Important Note regarding program content...
If your subaudible tone decoder is connected to a source that delivers more than one program and one or
more of the programs delivered does not contain subaudible tone signalling you may encounter (easily
resolved) problems. Any program that does NOT contain subaudible signalling tones probably DOES have
subaudible content. Normal music/voice and background noise can easily set off your decoder's outputs if
the audio is not (high pass) filtered. Programs that do contain subaudible signalling tones will always be
prefiltered at their origination point before subaudible tones are injected, thus keeping the natural low
frequency content of normal voice and noise from false tripping decoders down the line.
A good example would be an SCPC satellite receiver that you use for a couple of different network feeds.
One of the networks uses subaudible tone signalling for starting local breaks, the other uses DTMF Tones.
The network that uses DTMF tones probably does not filter out the subaudible portion of their program
audio. If you have a limited number of inputs on your console or automation system, you may not wish to
take up two inputs with audio from one source. Fortunately the CircuitWerkes Subaudible Tone Decoder
features a disable input. Connecting this line to the decoder's ground will enable the relays. You may
connect this line and the decoder's ground to a timed automation output that will sink to ground only during
the program whose tones you want to use. Any other time, the automation would unsink the disable input
and the tones will not cause relay closures. If you do not wish to use the disable function, a wire
jumper must be installed between the two screw terminals to enable the decoder.
