March 2005 QST Product Review:
http://www.arrl.org/members-only/prodrev/pdf/pr0503.pdf
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ICOM?s advertising for the PROIII
trumpets what it calls ?+30 dBm-class
third-order intercept point? performance
on 20 meters. This would put it on a par
with some of the best receivers we?ve ever
run through the Lab. Third-order intercept
(TOI) is a number that many like to
use as an all-in-one performance benchmark,
since its value derives both from
the receiver?s sensitivity and its front-end
selectivity (specifically, two-tone, third-
order IMD dynamic range). The more
positive the number, the better, and TOI
figures can also be negative.
Although the PROIII Instruction
Manual doesn?t specify the advertised TOI
number, an ICOM Product Guide, originally
in Japanese, spells out the measurement
conditions: 100 kHz spacing (wider
than our Lab?s widest 20 kHz spacing measurement),
preamps off and a 2.4 kHz filter
bandwidth.
Nonetheless, under the least stringent
measurement standard the ARRL Lab
uses, the PROII came pretty close to meeting
the +30 dBm mark. At 20 kHz spacing,
we calculated the TOI at +25 dBm
on 14 MHz with both preamplifiers turned
off. That works out to a slightly less than
a 5 dBm improvement over the PROII, all
other things being equal.
Under the same conditions at 5 kHz
spacing?something much more akin
to real-world amateur conditions (and
this time well within the passband of the
receiver?s 15 kHz roofing filter)?we
determined the PROIII?s TOI to be
?17 dBm, 1.8 dB better than the ?18.8 dBm
we calculated for its predecessor."
***********************************************
Whoopee...a whole 1.8 dB improvement
at 5 kHz for another $800? And (er......
ahem)...Orion's IP3 was measured by
ARRL at 5 kHz to be +22.1 dBm, a mere
39.1 dB better (for just $300 more) but still
below Icom's touted spec of +30 dBm. :-)
At least ARRL is getting a little tougher
than I've seen previously (last paragraph's
"real-world" comment). Some day they
may actually have the guts to call a spade
a spade in their reviews. Naah...not likely
as long as Icom keeps buying all those
advertising pages in QST.
73, Bill W4ZV
P.S. I finally broke the code...PRO stands
for PRO-fessional B.S.
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