[Amps] 4CX250 IMD

[Tom Rauch]

> At Ep of 1500 in AB1 3rd/5th is -30/35. However at 2000V 
> it slips to -23/27.
> This is a 2 tone measurement which disagrees with Toms 
> claim of Eimac using
> a single tone. Maybe they swing both ways (;

Hi Carl,

I actually said  (about a dozen times).......

"Eimac uses two tone IM referenced against a single tone of 
the test. The ARRL uses IM referenced against PEP."

I assumed people know a two tone test is a two tone test 
with two tones, and only the reference point changes. I 
assumed people know that a two tone IM test referenced to 
one tone of the two tones is a standard measurement method, 
which results in 6dB less favorable numbers than a two-tone 
test referenced to one tone of two tones.

For example (excuse my repeating it) a tube with -35dB one 
tone in a two tone test (Eimac's method) is actually -41dB 
using the ARRL method referenced against PEP.

The problem is everyone in the industry in the USA always 
used IM referenced against a single tone in two-tone tests 
and then around the time of the KWM-380 a few people changed 
to dB below PEP. This makes a 6dB discrepancy in the 
results.

A modern radio with -32dB PEP tone IM3 actually is the same 
as -26dB IM referenced against one tone of the two. THEY ARE 
BOTH TWO TONE TESTS.

73 Tom