On 23-May-10 10:45 AM, Jeff Blaine AC0C wrote:
> Of course, a real IMD test requires a 2 -tone source and you can download
> those applications on the web free of charge.
Wrong answer for amplifier testing. While you can approximate proper
"two-tone" testing with a sound card tone source when evaluating a
transceiver, a LOT more is required for accurate and technically correct
To do accurate IMD (and more correctly OIP3) testing on an amp, you NEED
two separate clean signal sources. This means two exciters that are
known to be very clean and free from harmonics (much greater than 60 dB
down) plus a high power combiner and usually a set of bandpass filters
at each of the tone frequencies. Plus, just to keep everything happy, a
bunch of attenuators sprinkled around the bench.
Anything less and you are only testing the source(s) and not the amp.
Some time back, W8JI detail the correct test setup for amplifier testing
and I think it's on his web site someplace. Anything less and you are
just fooling your self.
Larry - W7IUV
DN07dg - central WA
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