Ed your SDR-IQ will do a nice job of close in 2 tone ID testing, a
better job than my simple spectrum analyser. For IMD testing you do
not need a resistive coupler, an ordinary oscilloscope probe used with
a couple of turns of wire around the output coax outer will provide
sufficent signal for IMD tests (it is not suitable for power
measurement or harmonic measurement).
I have sent you via direct email a screen shot of my K3 and KPA500 2
tone IMD test viewed on a Perseus SDR. It allows simple and easy
measurement of each tone and you may be able to make similar
measurements with your SDR-IQ.
For harmonic measurement the bar is raised a little. You need a means
of sampling via a resistive coupler and/or high power attenuator. The
attenuator can be very expensive... The simple wire loop coupler which
works for narrow IMD measurements is not likely to have a flat
response across the HF and VHF spectrum.
You will also need a conventional spectrum analyser for harmonic
measurements, although you do not need one of the high cost narrow
bandwidth ones... One of 15 ~ 20 KHz bandwidth will suffice. There are
several on the market for $1500 or maybe less. I have a TTi PSA1300T
hand held analyser which sells for $1500 from Newark which is based on
a Palm TX PDA and offers the ability to take screen "shots" and store
them on a memory card. There are several low cost analysers from China
on eBay (around $775 plus import charges), however I have no
experience of them.
73 Dave, G4AON
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