Ron, WN3VAW, wrote in part:
> The important point is not that the ARRL has chosen their
> own method of test methods and procedures .........
> The important point is to make sure that the ARRL uses
> the SAME test methods and procedures on ALL equipment
> they evaluate. While this makes it difficult to do an "apples
> to apples" comparison between ARRL tests and others... by
> the way, which others?...
Well, the important "others" in this case are the engineers
within the Ten Tec engineering department: Doug Smith, KF6DX;
Jack Burchfield, K4JU; and Gary Barbour, engineers listed
by Scott in one of his previous activity updates on the Orion
program.
As some one else has said, it is absolutely essential that
the deltas in test figures be explained between what/how
numbers are measured in the ARRL labs and how in
the Ten Tec engineering lab. Ten Tec is claiming very
exciting performance numbers in their Orion performance
specifications. The ARRL right now seems poised to
counter those with, what appears to me, to be a really
awkward test procedure!! They really do not even measure
the IM products. The determination off IP3 and 2 is trivial:
just keep the amplitudes of the two test signals absolutely
the same and at some amplitude where an IM signal's
amplitude and frequency can be measure on, in this
case, an audio spectrum analyzer connected to the
rig output. Increase the amplitudes of the pair of
test signals exactly the same amount, say 3dBm.
Then measure, with the audio spectrum analyzer the
increase in amplitude of the 3rd order IMs seen on
the scope. If they are true 3rd order, they will increase
exactly 9 dBm; do this again, only increase the test pair
another, say 4 dB. Now the 3rd order IM product will
increase 12 dB.
You now have two points on the intercept chart graph. Connect
the points for each curve with straight lines; and where they
"Intercept" on the dBm in vs. dBm output graph is the
intercept point in dBm......very simple and straight forward,
and not depending upon previously measured other performance
numbers, as does the ARRL lab method using the "just"
barely perceptible IM showing up down at the MDS signal
level! For more clarification, see part 1 of Rohde's paper
in the Nov/Dec 2002 QEX publication.
73, Jim KH7M
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