[Elecraft] K3 and XV144 strange behaviour

2008-09-10 Thread Giulio Pico - IW3HVB
I noticed a strange behaviour during the last IARU VHF Contest last 
weekend.
With our team we managed to have a first field test of the rig 
coming for our experience with the K2/xv144 MHz combination the 
expectations were high.
The setup was composed by the K3 and a XV144 transverter, plus a Power 
amplifier, a preamplifier at the antenna (with some 30 mt of 1/2 
cellflex line) and two stacked 19 elements Log Loop Yagis.
The switching sequence was controled by an external sequencer drived by 
a foot pedal.
On the receiving side the combo was wonderful, the dynamic range allowed 
us to manage very well in the pretty crowded 2 mt band.

But we had some troubles mainly on TX.
Let say that our P.A. needs to be drived with circa 7/10 Watts at 
maximum (depending on the mode, SSB or CW). It's made from 2 x 4CX250B 
in push-pull configuration.
So I tuned the transverter to go from a range of 1 W (with -10 dBm drive 
from the KXV3 module) to a mazimum of 10 W (with 0 dBm of drive).
Things have worked pretty smoothly most of the time, but on a few 
occasions, we noticed a sudden loss of output power from the transverter 
(and from the P.A. of course).
Turning the K3 off and on again the transverter didn't power up. The 
XV144 label on the front panel flashed for a brief moment and then 
stayed off.
Changing band to HF and back again on 144 MHz (TRV1) and the XV144 
module powered up again. Not always on the first try.
Once powered up most of the times the output power was correct, but 
occasionally we had to do the procedure three or four times before 
coming back to normal functioning.


Any clues of the reasons of this behaviour???

73 de Giulio IW3HVB

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Re: [Elecraft] K3 and XV144 strange behaviour

2008-09-10 Thread Giulio Pico - IW3HVB

Before you ask...
Firmware Revisions: MCU 2.34; DSP 1.89.

73 de Giulio IW3HVB.

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Re: [Elecraft] K3 and XV144 strange behaviour

2008-09-10 Thread AD6XY

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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Re: [Elecraft] K3 and XV144 strange behaviour

2008-09-10 Thread Lyle Johnson

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.


Next time you set this up and *after* you have the drive set, set 
CONFIG:TX ALC to OFF.  Then see if you have the same problem.


If you are running SSB, you might also try setting CMP to 0.

73,

Lyle KK7P

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