Maximizing bits (optimizing audio levels)

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Maximizing bits (optimizing audio levels)

Postby kuggie » Tue May 15, 2012 9:16 pm

When setting up your RF node, there is an optimization we do to maximize the number of bits in the receive audio stream. This allows the greatest signal to noise ratio and can make the carrier squelch work better.

Using the "Radio Tune" menu the first step is to set the "radio tune rxnoise". There is no adjustment in the software - as this is done automatically, but you can optimize the input to the USB device (FOB - URI- etc.) by adjusting the amount of discriminator audio available from your radio. I do this by adding a potentiometer in series with the audio input (receiver audio) of the FOB. Many radios have an excess of audio, and some form of attenuation is needed, but you must also be careful not to cut the audio down too far otherwise the signal to noise ratio will suffer, and unreliable PL detection can occur.

The adjustment range of radio tune rxnoise is 1 to 16 and is done automatically to calibrate the USB device in software against the amount of audio that is available from your radio. When doing the rxnoise set-up, manually adjust the amount of discriminator audio (again with a control or resistors) into the FOB for a reading on the low side - to say 3 or 4. This maximizes the audio to the FOB without overdriving it. After optimizing the radio tune rxnoise, you must recalibrate the rxtone and rxvoice, and then do a "radio tune save" to store the settings in memory.

Hope this helps...
Kevin Custer - WJ8G

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