On 4/24/2014 4:22 AM, Carl Moreschi wrote:
The current Icom 13.8 volt rigs are generally worse, particularly the
IC-7600 and IC-7410.
The IC7600 is AWFUL. KE1B, 8 miles from me, drives an amp with one and
chews up 20 kHz of whatever band he's on. I recently did a series of
on-the-air measurements with another 7600 owned by KW6S.
The K3 isn't very good either.
That's VERY different from my experience. Indeed, I can look at my
panadapter and can easily spot a K3 by its MUCH narrower spectral plot.
My neighbor, K6XX, is 3 miles from me, and drives tube amps with a K3,
and I drive Titan 425s with my K3s. We can work 500 Hz apart on CW.
Something that's being overlooked in this discussion is the relationship
between output power, supply voltage, and IMD. K6XX, who works as an
engineer at Elecraft, including their KPA500, recently did a great
presentation to our club (NCCC) on "clean signals." IMD increases as
supply voltage decreases -- a rig will produce more IMD at 12VDC than
13.8VDC. Bob and I both own a Herc II, which has the practical virtue of
running on 13.8VDC, but which he observes isn't very clean. The KPA500
runs its output devices on 70VDC, which helps, but it's nowhere near as
clean as my Titans or his tube amps.
IMD also increases with output power -- a good rig will be cleaner at
the 50W level needed to drive most amps than when cranked ot rated
power. Early versions of Elecraft firmware allowed it to be cranked to
120W; early on, that was limited to 110W to reduce IMD.
Bob also noted that a good tube amp is inherently cleaner than a good
solid state amp IF it is carefully tuned, and that solid state amps are
cleaner when working into a matched load.
As to John Henry's comments about "are hams willing to pay for a clean
rig?" A major part of Elecraft's success is that their customers ARE
willing to pay for it. I also note guys lined up to by $10K rice boxes,
dirty or clean.
More to the point, though, is that those rigs that are dirty result in
their owners VIOLATING FCC Rules when driving an amp. As my mother
taught me when I was a child, "just because Joe does it doesn't mean you
should do it, and it doesn't make it right.
73, Jim K9YC
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