Connection to the receiver
**SC** None of this section is applicable to using a wattmeter.
Start by looking at the various audio outputs available on your receiver. To use triggered readings you must use Line In on the sound card because the microphone input is not stereo.
If you have a fixed level output that does not vary as you change the AF level on the rig then go for that as first choice. Most rigs have one of these outputs intended for connection to a recording device, phone-patch etc. Determine its output level and quoted impedance and then decide whether it best matches either the line-in or microphone inputs of your sound card. Some rigs have a 200mV into 600 ohms, OK for line-in; others have 20mV into 10K, OK for most microphone inputs.
If you do not have a fixed level output then go for headphones output next. The down-side of this is that your rig's speaker will usually be disconnected, but you can still monitor the audio through the sound card's output.
Your last resort is speaker output, though you must really know what you are doing when it comes to signal levels.
Headphones output into line-in, a fixed level 20mV recording output into the microphone input, and a fixed level 200mV recording output into line-in have been found to work satisfactorily. In all cases go for the best match in impedance and signal levels.
Appropriate precautions to avoid damage to the computer should be taken. In particular, grounding of both receiver and computer is vital and a series capacitor in the line or better still an isolating/matching transformer should be used.
Once you have settled on either line-in or microphone then tell PolarPlot which of the inputs you want it to control by clicking on the 'Choose input' button and following the instructions on the screen.