K3 serial 499 build and operation

[A.K.Forrest]

Dear all,

finished building K3/100 0499 about a week ago. Took me three days of
not full time effort. No problems or missing parts. Everything went by
the book. Operating did cause some problems to start with. The
configuration and initialisation didn't work to start off with. I did
not realise this. The symptoms were producing 84 watts with a 50 watt
demand and not being able to get a low frequency audio response out of
the standard filter, fine on the others. Setting up the filter offset
correctly and doing the transmitter and watt meter initialisations again
cured the problem. I don't know if updating the firmware overwrote my
settings. I will probably never know. I get the standard 47 watts out
for 50 watt demand using the watt meter in an ACOM1000 amp as reference.
I also didn't get the AFX effects until reading on the list to set
number of speakers to 2, thanks. I use a Mac mostly so used the Mac
firmware update utility. It works really well and its very nice to get
support for the mac. Most radio software ignores the Mac.

Ease of operation is great. The bandwidth choosing controls work
beautifully. The response appears to be completely flat across the audio
spectrum as measured with the MixW spectrum display. This is a very
welcome change from the K2. Setting up the frequency calibration to
better than a Hz was also very easy, again in contrast to the K2. The
general ergonomics are very good, I even dared to operate split with no
problems. The PA appears to be extremely robust. The PA temp rises very
little even with 50 watts continuous digital modes and I can't hear any
fans activity over the noise from my computer. SSB operation is very
smooth. Couldn't resist trying out the K3/10 before putting in the amp.
Called a German station on 40m  and got a reply and 59 first call. I'm
very happy with the whole radio.

Now the less good news. I appear to have lost about 3db of IMD transmit
performance compared to the K2. I use a KK7UQ IMD monitor for PSK31 and
am now often getting -27dB rather than the usual -30dB or better on the
K2. These figures don't seem to be very power dependent and I don't
think theres going to be a firmware fix, although performance is still
in the top half of signals I see on the bands. The second thing I am
noticing is ghosts in the waterfall display of MixW. I assumed that I
was driving the audio card too hard and getting harmonics, but this is
not the case. The ghost signals do move faster across the waterfall than
the tuning rate implying harmonics but I can decode the ghosts, so the
bandwidth of the ghost signals has not changed which it would do with a
harmonic. Ghosts are about 20-30db down on the correct signals, outside
of the chosen radio pass passband. I'm sure I didn't seem them with the
K2. They appear to have no effect on the actual decoding of digital
signals but I'd like to know what they are.

Someone mentioned having to follow PSK signals across the band as each
over occurred at a slightly different frequency.  There are plenty of
fixes involving keeping the transmit frequency fixed and using RIT, but
I've seen the same thing, and am interested to find out how this is
happening.  One possibility is that MixW and other programs can have an
offset between receive and transmit frequencies. When I looked in the
mode settings for PSK on MixW they were 3Hz apart. I even noticed send
and receive offset when talking to another K3, but I am pretty sure this
is a software not radio problem. Some contacts have zero offset.

Overall I highly recommend the K3, its a joy to use (and fun to build).
Looking forward to the sub-receiver, panoramic displays etc.

Andrew Forrest
M1KAZ (K2 #3679,K3 #0499)
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