[Elecraft] [KX3] Digital TX issues

[Gary Hawkins]

Just as background, this digital setup has been working successfully for 
several weeks and as I mentioned in another post I've recently had over 
170 contacts in both JT65/JT9 running 5 or 10W (my KX3 has 3rd third 
party heatsink).  The ALC was appropriately set based on information Don 
provided several weeks ago but it was the first thing I checked.  The 
mic level was set for 5 bars ALC.

After the last problem, I checked all connections and setting and 
everything seemed correct.  The PSU was stable at 13.4V and VSWR sweep 
on antenna did not show any problems.  I connected rig to a power meter 
and dummy load and brought up all the s/w.  Things started working 
again.  I then put the radio through a 12 cycle CQ sequence at 10W.  
Again all good.  I reconnected the antenna and started attempting to 
QSOs.  PSKreporter showed I was getting out and then I worked two QSOs 
without issue.  However, on the third QSO, on the second transmission 
block the TX power collapsed (KX3 TX light still red) I think midway 
into the transmission - I halted TX on WSJT-X.  I tried the tune 
function on WSJT-X and while the KX3 TX indicator comes on there was no 
TX power.  ALC shows zero bars.

Thus, I would have to conclude the problem is an intermittent behavior 
rather than setup issue.  It seems to me the KX3 TX is shutting down in 
response to some fault condition.  PA temp is well below max, and no 
other error messages are observed.  Unlike when the unit powers down due 
to high temp, the power setting remains at 10W.  ALC shows zero bars.

While trying the tune function on WSJT-X after fault condition, I 
increase mic gain and ALC bars start to briefly show and TX power 
briefly flickers on power meter.  However, within a second so the ALC 
bars drop back to zero and so does the power.  Increasing the mic gain 
again results in similar behavior.

I switch all equipment off and call it a night.  This morning, I bring 
anything up again and the KX3 will not radiate power in digital mode 
albeit the TX light is ON.  Transmitting in FM the radio seems to be 
working!

Again, thoughts would be greatly appreciated.

73's Gary K6YOA


    That is a typical behavior when the KX3 (or K2 or K3) is not
    provided with sufficient audio drive.  It "power hunts".
    Increase the soundcard audio output and/or the mic level to produce
    4 bars with the 5th bar flickering on the ALC meter.  Set the power
    level with the power knob.  Attempting to control the power level
    with the audio drive will result in failure.

    73,
    Don W3FPR

        On 7/12/2015 8:39 PM, Gary Hawkins wrote:

        I'm seeing a odd problem working digital today with my KX3.
        Sometimes when I go into transmit (power set at 5W) JT65_HF, my
        Signalink shows PTT active (red light) , the KX3 shows PTT
        active (red light) but no power is being radiated. Antenna
        (dipole) has a near perfect match to the KX3.  Power still shows
        set to 5W on KX3. Problem remains if I switch from the antenna
        to a dummy load.  Osc and PA temp at 36 and 30C - PSU stable at
        13.4V.  When I try to transmit is DATA A mode (tune) power seems
        to try to ramp up and then immediately falls away.  Radio seems
        to transmit fine in FM mode.  What am I missing please?