Thanks for the explanation Wayne.
Dave Wilburn
K4DGW
K2/100 - S/N 5982
wayne burdick wrote:
AB2TC - Knut wrote:
Receiver results as expected, great. Disappointed with the transmitter
IM,
even at reduced power.
A couple of comments on this, Knut.
The league measured around -30 dBc worst-case when using the K3's highly
accurate internal 2-tone generator (as did we). 12-V class radios are
rarely better than -30 dBc on their worst-case band, and some are in the
-23 dBc range, based on a survey of QST reviews from the past 5 years
(more on this below).
QST's published -27 dBc figure was measured with an external 2-tone
generator via audio injection (this is the ARRL's reference method).
This was disappointing for us, since we were expecting -30 dBc. The fact
that they did see -30 with our internal 2-tone generator suggests that
the SSB setup procedure in the K3 manual, and/or our SSB ALC algorithm,
could be improved. We're looking into this already. Any improvement we
make in firmware (or hardware, for that matter) will immediately be made
available to all K3 owners.
Transceivers that are very heavy (including some that probably have
their own zip code) can incorporate a large internal or external power
supply that provides greater than 12 V (typically 24 to 50 V) for
improved PA-stage overhead. Some can even be operated class A, which I
applaud. But neither greater weight nor class A operation near 100 W is
possible in the K3's form-factor. At just over 8 pounds, it's portable.
This *was* a design goal :)
QST always publishes the worst-case per-band IMD number, in our case on
12 meters. On most bands, IMD is much better than this by any
measurement method, exceeding -40 dBc in some cases. The worst-case IMD
is also much better if you're running less than 100 W. So, anyone
driving an amplifier that requires less than 100 W to reach full power
will see even better numbers.
My question to Elecraft is: If this had been a
factory assembled unit, would it have passed QC at Elecraft?
There is no difference in measurement method or performance between kit
and assembled. The 10-W and 100-W modules are all pre-tested before they
go into either the radio or the parts kit. The RF boards are also 100%
pre-tested, and any problem with IMD would show up immediately. But IMD
is generally a non-issue for the RF board, which at the 0-dBm transmit
drive point shows worst-case 3rd-order IMD of -45 to -55 dBc.
I'm sure this unit passed our QC tests, given that the League found -30
dBc worst-case with the internal 2-tone generator.
73,
Wayne
N6KR
---
http://www.elecraft.com
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