[Elecraft] [KX3] Digital TX issues

[Bob McGraw - K4TAX]

While your test using a dummy load seem reasonable and correct, it would 
appear as though you may have an excessive amount of Common Mode current 
on the feed line, not being seen by the SWR indication in the radio.  I 
suggest a Common Mode choke on and at the output of the radio.  Perhaps 
a fault with a antenna or coax jumper or associated connector.


73 Bob, K4TAX


On 7/13/2015 11:35 AM, Gary Hawkins wrote:
> 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?
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to rmcgraw at blomand.net
>
>
>