Something made me look up the January 1993 QST review of the OMNI VI and
check its transmit IMD stats. The reviewer, Rus Healy, says (p. 67), "As
Fig 1 shows, the transmitter's third-order IMD products are down almost 40
dB, which is excellent for a rig with 13.8-V final-amplifier transistors."
The QST review (11/00) of the FT-1000MP Mark-V says only, "The original
'MP did pretty well in the IMD department, with worst-case third-order
products down about 27 dB and fifth order products down about 43 dB (this
was on 24.95 MHz)." With regard to the Mark-V, the reviewer, Rick
Lindquist, focuses on the Mark-V's built-in Class A amplifier for its clean
output. There is no mention of Class A-B results but, according to the
graph accompanying the review, in Class A-B (i.e., normal) operation, the
Mark-V's third-order products are 27 dB down and fifth order are 48 dB down
(21.250 MHz), virtually identical to the earlier 'MP's results.
Yaesu's final amplifiers in both the 'MP and the Mark-V have yielded 13dB
worse IMD performance (albeit at 200 watts) compared to the OMNI VI's final
amplifier, and by so doing they have met a (new to me) "doing pretty well"
standard for third-order IMD products enunciated in the Mark-V review,
which I take it lies somewhere between "excellent" on the one hand and
"godawful" on the other.
Note also ARRL is reporting in the May QST that the worst-case third-order
transmit IMD number for the IC-746PRO is 25 dB down. I don't know if this
means the IC-746PRO also has cleared the "doing pretty well" criterion.
73,
John, W3ULS
|