CTCSS Encoder / Decoder Board
For Two-Way Radio Applications
Actual Size CT-30 PC board.
(Click image to enlarge)
Schematic Image - Click to enlarge.
This board will provide quality logic signals for driving a repeater controller or other radio interface device.
It requires a few hundred mV RMS of discriminator audio and a source of DC power.
If you purchased our kit, refer to the parts list and make sure you have all of the components
you need to build the kit.
Click here for Parts List.
If you need assistance with the assembly, Click here for assembly instructions and construction notes - with large photo.
This device is intended to be installed inside a radio or project box for protection. Refer to the schematic for the pinout of the DB25F where all of the logic signals, power connections, and discriminator audio input is listed. Pin 16 on the DB25 can be used to supply discriminator audio to your controller or other audio interface.
Click here for DB25 and other board connection assignments.
Setting the CTCSS tone frequency:
Click here for DIP switch settings.
1 = ON
0 = OFF
In the photo at the top of the page, the CT-30 is set to 123.0 Hz.
Recommended powering requirements:
The board requires a recommended minimum of 7 VDC to put the regulator into full regulation. The maximum recommended voltage is 16 VDC, however, the voltage regulator will survive up to 24 VDC before damage occurs.
Recommended discriminator audio input level:
For best CTCSS detection and dynamic range, an input of at least a few hundred mV RMS of raw discriminator audio at the input of the board is required. This equates to about .85V peak to peak at a minimum. 750mV RMS (about 2.1V peak to peak), is about the maximum amount of audio that should reach the input of the board. If you have too much audio, a simple resistor divider in series with the input will reduce the input to a more desirable level. Input levels are somewhat dependent on the type of receiver, characteristics of the discriminator. If you have too little audio, a simple audio amplifier may be required to meet the required input level of the board. Refer to this amplifier project (the first one) if necessary.
Explanation of the logic signals and other pins:
Both active high and active low logic outputs are available on the DB25. In addition, optional open collector outputs are available from 2 holes on the circuit board. These optional outputs can be used for operations that are beyond the original scope of this board.
A pull-down resistor is included on the logic high output. Obviously if you are using this board and need an active low output you should be using the output connected to the NPN transistor, but, the on-board pull-down resistor can make circuitry respond correctly when using the active high PNP output. Likewise, a pull-up resistor is included on the logic low output for the same reasons.
All logic is sourced from +5V and ground. +5 volts is the logic value expected directly from the collector of a PNP logic transistor that is biased on. Ground is the logic value expected directly from the collector of a NPN transistor that is biased on.
The normal logic outputs that connect to the DB25 should satisfy most of the equipment you'll connect to this board. For those instances where they don't, you can use the optional outputs labeled A - B. These outputs are available from "holes" on the circuit board, marked A - B on the silkscreen. These outputs connect directly to the collectors of the logic transistors before any current limiting resistors. There are six extra pins on the DB25 pins 7, 11, 12, 15, 24, and 25 which can be jumped to any of these additional outputs. Caution should be given to the use of any of these additional outputs as they are unprotected, and misuse will cause switching transistor failure. While the PNP transistor has the over-current protection of the 5 volt regulator, there is no protection for the NPN to ground. Be certain that your connection to these outputs don't exceed the capabilities of the board or switching transistor.
The SJ1/SJ2 header allows the PTL function to be selected remotely. Normally, this jumper will be in the SJ2 position - which enables audio on the RX Out continuously, as long as PTL or pin 14 is not grounded. Selecting SJ1 gates the filtered audio when the decoder is not decoding a tone, and passes audio when the red LED is lit. Refer to the manual download below to see what this function is, what it does, and how to use it.
Information on the FX465.
Click here to download a manual for the FX465-D5
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Product of Masters Communications, all rights reserved.
Specifications may change without notice.
Images property of Kevin Custer - W3KKC
Board layout by Chuck Kelsey.
HTML December 7, 2015, W3KKC All Rights Reserved!