Very true on all of your points, but the initial question was about the IP3
of receivers, so the mixer specification is what is being talked about here,
not amplifiers. When characterizing amplifiers, you have either input IP3 or
output IP3 to contend with, so it gets a little bit more complicated.

The formula I quoted IP(n)= Pin + (delta P/n-1) is a classical
derivation of a 2 tone result in the passband of a broadband circuit
such as an amplifier. Delta P is the difference in the output tone level
and the intermodulation product level. You can use it for the input IP2,
IP3, et etc. The formula can be used to calculate any intermodulation
product as long as the following conditions are met:

1. The tones and intermodulation products you want to make a measurement
on all have to be in the circuits passband.

2. You have to be in the circuits linear range.

3. You have to be within the dynamic range of the measurement equipment.

The Mini-circuits pdf is about a making these measurements on a mixer
and so it requires a third generator as the Lo.

IMR is intermodulation ratio. The definition appears to be the delta of
the input tone level power and the measured spurious response, which is
the intermodulation product I speak of or in other words is a difference
dBc (dB below carrier, this being the input tone).

No, we are talking about the delta between the 3rd order product and its
associated tone at the I.F. (output) port of the mixer under test.

This being the case
then IP3 = Pin + (IMR/2) has the same meaning if there is no gain. If
there is gain then you would get a different answer. I think you are
better off using the formula I referenced as both input power and gain
or loss are accounted for.

True.

The test setup has several amplifiers so I don't know how they actually
expect to make a measurement on the DUT.

Actually, this is very easy........those amplifiers have a very high IP3, so
they introduce very low measurement error.
This setup will allow you to have an IMR of at least 110dB. I didn't have
those amplifiers on hand, so I used circulators for the required isolation
when I characterized that MCL digital step attenuator.

Also troubling to me that they
state the IP3 measurement can only be made at some input power level and
that it you will get a different result at a different input power
level. Well, you will get the same result at different power levels as
long as you account for it and conditions #2, and #3 above so I don't
understand their problem with that.

As long as you are within the linear range of the DUT, this is true.

They are also using filters. Using filters is OK as long as you don't
violate condition #1 above.

If you are using low-pass or bandpass filters at the output of each
generator and make sure that the tones are at the required level, this is a
non-issue. Sometimes, you might only have a filter that has a corner
frequency very close to your highest frequency of interest.
Part of calibrating the test setup is making sure that you have the correct
power level at every frequency that you are making the test at. What I would
do is measure the power level of the RF generators and LO generator at every
frequency of interest, and either use a correction factor for setting the
generator output manually, or I would enter the correction factor into the
Labview program when applicable. Since we are making sure that the power
levels are correct at all frequencies, condition #1 is being met.

--
Telamon
Ventura, California

On a final note, I haven't done any multitone testing of
amplifiers..........my tests were limited to harmonic distortion, noise
figure, S-Parameters, and 1dB compression point.
As I have mentioned in the past, it sounds like you have been in the
industry, and I appreciate your input.
One thing I didn't mention was a piece of test equipment that makes these
tests a little bit easier. Instead of using a swept spectrum analyzer, a
Vector Signal Analyzer (VSA) is used. This instrument has a very wide
dynamic range, with a noise floor of -140dBm, even in a very wide passband.
Since this is really an FFT analyzer vs a swept analyzer, you aren't limited
by very long sweep times of the swept analyzer.
Another new tool that has become available from Agilent is the PSA. This is
a spectrum analyzer with added functions, but the best thing about this
analyzer is the very low sideband noise from its internal LO.
This makes it possible to look at the phase noise sidebands from an 8657 for
instance, even at 1MHz away from the carrier.
There were several different generators from Agilent, Rohde and Schwarz, and
Fluke, but the quietest units they had around were still the 8642B. When I
characterized one of those unit at a 100kHz offset, I measured the noise
down at -154dBc.
The new R&S stuff isn't bad, but the 8642 generators are still "king of the
hill".

Pete