Some important points before you start building your cable.
1) How to disable the RF Circuit:
The transmitter should not transmit radio signals while you use it for simulation.
Plugging in the cable into a turned-off transmitter should turn it on, keeping the RF circuit (The part of the transmitter that actually transmit radio signals) off.
If the RF circuit is not off for some reason you should take one of the following actions, in order to prevent the transmitter from transmitting:
Remove the Synthesized Transmitter Module
OR
Remove the crystal from the transmitter
2) How to protect your hardware:
In most cases, your transmitter is protected from overloading by means of a fuse and your sound card is protected from over-voltage by several overflow diodes.
However, you can add a simple protection circuit to your cable:
Using a tx with a simulator...(with home-built cable)
3) How to convert a stereo jack into mono:
It is recommended to use a 3.5mm mono jack for the computer end of the cable.
However, you can easily convert a 3.5mm stereo jack into a 3.5mm mono jack by tyeing the terminal of the right audio channel to the ground terminal:
Using a tx with a simulator...(with home-built cable)