Hi, All.
Thanks to all who responded about the power output being the same
between 20m and 40m.
I was able to run some tests with a recently calibrated HP8591A
spectrum analyzer, and I thought I'd share my results. (I also had a
chance to calibrate the KXAT1 it was reading about 0.25W high).
My battery voltage was: 9.1V key-up and 8.2V key down.
I was hooked up to the analyzer through a recently certified precision
10dB attenuator and a recently certified low loss coaxial feedline.
(I've adjusted the fundamental power below by 10dB for the pad).
Fundamental 2nd 3rd
4th 5th
Band Power Harmonic Harmonic Harmonic Harmonic
(Adjusted Pad) Delta Delta
Delta Delta
80m 30.6dBm (1.15W) -45dB -66dB -76dB -76dB
40m 29.4dBm (0.87W) -39dB -52dB -59dB -64dB
30m 30.4dBm (1.09W) -40dB -70dB -72dB -71dB
20m 30.1dBm (1.02W) -60dB -66dB -70dB -69dB
Observations:
The harmonic rejection is within specification, at least at 1W out. I
assume that the level of harmonic suppression (delta) will remain the
same regardless of the power out, I'd be interested in comments on
that assumption as I did not have the right connector to run the radio
on 12V to hand when I made the measurement.
I do NOT have the 20m power being 0.3-0.6W lower than 40m (any more -
it was before the KXB3080 mod), in fact I have almost the opposite
(0.15W more power on 20m than 40m), and I assume that difference would
be more pronounced at higher output powers. The manual states that my
harmonic rejection may therefore be sub-optimal:
"If both bands have adequate output power but 20 meters is higher, you
should adjust the windings of toroidal inductor L2. To do this,
"squeeze" the turns of L2 together slightly so that they occupy only
about 70% of the core's circumference. With L2 at its optimal turns
spacing (for best harmonic rejection), 20 meter output will be about
0.3 to 0.6 watts lower than 40 meters."
The worst case harmonic rejection seems to be 40m with the 1st
harmonic being -38.7dB down from the fundamental, but that's close
enough to the specification (-40dB) I think. Should I be trying to
squeeze my turns to improve it? I'm not sure.
I did compare my results to John AE5X's measurements for his KXB30 KX1:
KX1 2nd 3rd 4th 5th
Owner Band Harmonic Harmonic Harmonic Harmonic
Delta Delta Delta Delta
AE5X 40m -40dB -53dB -60dB -66dB
VA3SIE 40m -39dB -52dB -59dB -64dB
AE5X 30m -35dB -63dB -71dB -68dB
VA3SIE 30m -40dB -70dB -72dB -71dB
AE5X 20m -58dB -60dB -73dB -70dB
VA3SIE 20m -60dB -66dB -70dB -69dB
So the KXB3080 low pass filters apparently offer superior harmonic
rejection compared to the KXB30 except on 40m where it's slightly
worse, although in practice the 1dB difference is probably close
enough.
Perhaps I could improve the 40m harmonic rejection by squeezing turns,
but it probably isn't worth it for 1dB.
I hope others can benefit from these measurements.
73
Martin.
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