[Elecraft] KX-3 TX current draw?

[Drew Arnett]

To follow up on Victor's point, did some more measurements this morning.

Setup:
KX-3 minimal adapters to 40 dB directional coupler to load
terminated unused port of coupler
measured port through 3 ft patch to Kanga US AD8307 RF power meter

I have good calibration data for the power meter, but for the purpose
at hand, I won't correct the meter readings.  60 on the scale is about
-20 dBm.  Every 10 on the scale is actually 10.7 dB.  Good enough.

Internal tuner bypassed.

Measurements:

Note:  RX current in RX was between about .15 and .19 A for all 3 bands.

14 MHz @ 1 W setting
13.7 V RX (per KX3)
13.4 V TX (per KX3)
1.15 A TX (per KX3)
VSWR 1.3 (per KX3)
FWD 67 (on power meter display, very close to expected)
REV 30 (on power meter display)
--> return loss approx 37 dB

28 MHz @ 1 W setting
13.7 V RX
13.4 V TX
1.15 A TX
1.3 VSWR
FWD 67
REV 30
--> return loss approx 37 dB

50 MHz @ 1 W setting
13.7 V RX
12.9 V TX
2.9 A TX
1.6 VSWR
FWD 71
REV 35
--> return loss approx 36 dB

Hmm.  So, I'm seeing 3% or less efficiency.  Only one respondent on my
query about TX current draw, and he was getting 15%+ efficiency.  No
wonder my PA temp shoots up.

Thanks,

Drew
n7da

On Sat, May 9, 2020 at 11:25 AM Drew Arnett <arnett.drew at gmail.com> wrote:
>
> Good point, Victor.  And why I included that SWR reading.  Other bands
> read fine.  I have high confidence in the load and adapter (tried
> swapping both just in case).  I could measure the load and adapter the
> next time I'm in the lab at work if I want to be absolutely thorough,
> but it is a microwave load and just adapting from BNC to N (no coax).
>
> SWR looks fine on other bands.
>
> Thanks,
>
> Drew
> n7da
>
> On Sat, May 9, 2020 at 4:57 AM Victor Rosenthal <k2vco.vic at gmail.com> wrote:
> >
> > I think 1.6:1 is high for that kind of dummy load, if it's in good shape. Should be close to 1:1.
> > Anyway, you can't really say there is a problem unless you have a better match. Current draw is sensitive to mismatch.
> > --
> > Vic
> >
> > On May 9, 2020 2:32:15 AM GMT+03:00, Drew Arnett <arnett.drew at gmail.com> wrote:
> >>
> >> Walter,
> >>
> >> 50 MHz TX constant 4 W carrier measures 13.53 V on DMM (outside the DC
> >> power plug), 13.3 V on KX3 meter, 2.9 A on KX3 meter and 1.6 to 1 VSWR
> >> on KX3 meter.  Microwave dummy load with BNC to N adapter.
> >>
> >> I didn't measure all of this when the rig was new, so have no baseline
> >> to know what is normal.  :-(
> >>
> >> Thanks,
> >>
> >> Drew
> >> n7da
> >>
> >> On Fri, May 8, 2020 at 11:19 PM Drew Arnett <arnett.drew at gmail.com> wrote:
> >>>
> >>>
> >>>  What do you see for current draw on the KX-3?  Manual says 1 to 2 A typical.
> >>>
> >>>  I'm seeing 3 A at less than full power on one band.  Yikes!  Makes me
> >>>  wonder if the repair shop is open?  Elecraft website says hunkered
> >>>  down and mostly work from home.
> >>>
> >>>  Thanks and best regards,
> >>>
> >>>  Drew
> >>>  n7da
> >>
> >> ________________________________
> >> 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 k2vco.vic at gmail.com