Don Wilhelm wrote:
Third order blocking IMD is quite another thing - there are many
variables to consider. The best that we can hope for is that the
'standardized' tests will provide a good indicator of the performance
on the real world - a receiver with narrow 'roofing filters' should
excel in that test - although the test reports should specify the
filter widths.
Rob Sherwood always specifies rig settings/options -- don't know about ARRL.
Not so much, I don't think. This should be done universally, and in detail.
The devil is definitely in the details here.
That said, I believe real-world performance can be expected to pretty much
follow the bench metrics, based on my own limited experience (especially on
the negative end). To wit:
Some years ago, before I was dry behind the ears in terms of understanding
receiver design concepts and metrics, I acquired a Kenwood TS-2000, seduced by
its sexy looks, multi-band multi-mode capabilitities, and so forth.
Having used this rig on 6M under difficult contest conditions (extraordinarily
strong sporadic-E openings with many S9+40 signals) over several years, I can
tell you for sure that this rig absolutely falls on its derrière in the
presence of nearby strong signals. It is the next thing to useless as a
contest radio, especially on SSB. (I don't think much of it on CW, either.)
Subsequent to my acquiring it, Rob Sherwood came out with his 2 kHz dynamic
range metrics, and these showed the TS-2000 to be almost at the bottom of the
pack in terms of 3rd-order IMD dynamic range (57 dB). ARRL's numbers pointed
in the same direction, though they only measured to 5 kHz separation.
This experience made a believer out of me, as the test data exactly
illustrated my own on-air experiences with this whoreson dog of a radio. ;-)
On the other end of things, the TenTec Orion and Orion II continue to be the
contesters' radios of choice, despite the plethora of problems both these
radios have had with design, manufacturing, and firmware. I doubt that
steely-eyed contesters are going to stick with a problematical radio unless
there is really something going there in terms of basic performance that they
can't get anywhere else. At the end of the day, it's dyanamic range, dynamic
range, and dynamic range.
So yes, I do believe in receiver bench metrics!
Bill / W5WVO
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