On receive we had persistent problems with people using lesser receivers and
similar transmit power not being able to copy us because of QRM. DLs
especially. We heard many very strong signals but none excessively wide. 

We also had system problems though not the same, or at least the same but
partly fixed.  In our case the 9-way D connector was at fault, unless fully
screwed in it was found to not be making a good contact. Fully screwing it
in fixed that of course, nothing to do with the K3. 

Our main K3 related problem was the inconsistent power output. We were also
using a pair of 4CX250Bs, parallel rather than push pull. To avoid over
drive splatter, the amplifier trips out if any significant grid current
occurs. The power spikes I have noted before made tuning up the drive with
the PA on impossible. The correct drive was set, in incremental steps with
the spike dealt with by keying with the PA off for the first transmission,
then enabling the PA and seeing if the drive was sufficient. Once set the
power would not stay fixed, it would sometimes drop by maybe 2-3 dB. Just
adjusting the power one step up or down brought it back but with the usual
initial spike that would on occasion trip the amplifier protection. After a
couple of overs the power would drop back again.

While setting up we also did some transmit cleanliness checks with local
stations. The K3 + XV144 at about 7W output driving the pair of 4CX250Bs was
reported to be exceptionally clean with very good audio.

Considering this, the K3 plus XV144 while probably the best combination I
have ever come across on receive is not ready for use on transmit just yet
because of the ALC issue if you use a sensitive amplifier.

One other minor point, with large chunky VHF coaxial relays, the 20mS TX
delay is not quite long enough, but still much better than those rigs with
no TX delay at all! You probably still need a sequencer.


Mike



Giulio Pico wrote:
> 
> Before you ask...
> Firmware Revisions: MCU 2.34; DSP 1.89.
> 
> 73 de Giulio IW3HVB.
> 
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