VKRWA - Tone Access

For those Amateurs that have older equipment that does not have the ability to generate sub audible tones we would refer you to the following PCB's and Kits  that are made available by the Waverly Amateur Radio Club in New South Wales.

http://www.vk2bv.org/2001-website/w_freq.htm#F0

In addition to the Waverly Club information here is a link to the original designer's instructions and installation information for a few of the older rigs.

http://www.vk2bv.org/w_ctcss.htm

CTCSS??? 

Why???

In this age of electronics with IT, elaborate communication systems, computers, electronically controlled industrial and domestic devices and general interference from power lines etc. all this crud can enter the circuitry of repeaters locking up the system and timing it out. So we need to control our repeaters so that only our equipment can operate it. This can be achieved by fitting a circuit to the repeater which allows the transmitter to be turned on by a low frequency tone which is below the audible range of the modulation of the transmitter. This sub-audible signal is supplied by the user’s equipment and must be generated constantly to hold the repeaters transmission open.

How???

An encoder device, which is an oscillator tuned to the correct frequency, is these days retro-fitted to the transceiver we own. If not it has to be installed to it. This oscillator when turned on has to run constantly and has to be fitted to the modulation circuit after the normal modulation has been generated. The reason for this is that the microphone output is usually processed by the audio circuits in the amplifier to limit the audio response and gain to give the best input to the modulator and would not pass the CTCSS tone.

Requirement???

The encoder can be fitted at a convenient site and requires normally 5 to 12 volts DC which can be connected permanently so no on/off switch is required. The frequency generated must be correct for the repeater to be used. The encoder input should be set to give a deviation of the transmitted signal of 0.5 to 0.7 KHz and set when the microphone signal is not present.