[AMRadio] Two tone audio generation

Jim Candela jcandela at prodigy.net
Fri Aug 4 12:03:36 EDT 2017

When doing distortion tests, be it harmonic, or intermodulation tests (2 tone), the audio source needs to be MUCH cleaner than the system being tested. That said, a super clean audio source that is hooked up in a way that introduces some hum, or has RF intrusion into the audio source will certainly "muddy up" the results. The audio source must be well shielded, and free of ground loops. Also, the RF issue can be minimized by using a good dummy load. Computer based audio sources can be very clean, and some not...A lot depends on the D-A and audio output circuitry (sound card).

Some of the audio sources mentioned thus far will not be clean enough. The Cumbria and the Elecraft boards advertise -50db distortion (0.1%)...but those are raw boards with no shielding, or enclosure...The cumbria also has a single adjustable tone whereas the Elecraft only has two fixed tones. I have bought two XLOCK's from Cumbria, and they are a first class company with well engineered products.



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