[Elecraft] KX1 sn 379

[Rick Hampton]

Hi, Ron.

Well, I had a few minutes tonight, so I went to the Fortress of Solitude and did
some checking.  After looking at the main board again, I notice L1 was
essentially leaning against L2.  After twisting the two slightly so they were at
45 degrees to the back of the board and with some separation, the note on 20
meters sounds much better with the turns on L2 adjusted according to the
manual.  Apparently, it was some coupling between the two inductors that was
causing the problem.

Mind you, the values below are from the ATU only adjusted according to the
manual, so they're only in the ball park, not adjusted to a calibrated watt
meter.  After "calibrating" my NoGA watt meter to the ATU, I get results
consistent with the ATU.  (Someday I'll get these things REALLY calibrated.)

With 12.3 VDC during transmit from a gelcel:
7100 = 4.1 W
10106 = 4.7 - 5.0 W
14100 = 3.5 - 3.8 W

At least they now look a lot more reasonable, if not nearly identical with your
values.

I'll see if I can sneak some time at work in the next couple of days to see what
the output looks like on the spectrum analyzer for the three bands.  If I see
anything unusual, I'll send you a screen shot.  Thanks for taking the time to
dig up the spectral purity numbers for me.  That was a real time-saver.

Rick, WD8KEL

Ron D'Eau Claire wrote:

> I haven't tried to adjust the KX1 the way you did. You might be right about
> the coupling causing the rough note. You should be okay as long as the
> signal on the auxiliary receiver isn't abnormally-strong (less than S-9).
>
> The ELECRAFT specs for the KX1 provide for all spurious emissions, including
> harmonics, to be at least -30 dB down (the manual says -30 to -40 dB down).
> This agrees with the FCC requirements for transmitters with a "mean" power
> out of less than 5 watts which says "the attenuation must be at least 30
> dB." (Part 97.307 paragraph d).
>
> I suggest adjusting the turns on L2 as described on page 59 of the manual so
> the output on 20 meters is somewhere between 0.3 and 0.6 watts below 40
> meters, and then see how the signal sounds. I've not run into anyone who had
> a rough note that was controlled by the spacing of the turns. I agree, it
> sounds like a parasitic since you can adjust it with small changes in the
> inductance.
>
> Be sure the source power is "clean" when you check the note. Batteries are a
> good idea, just to be sure something funny isn't happening with the power
> source when you xmit.
>
> Ron AC7AC
>
> -----Original Message-----
> Hi, Ron.
>
> Well, yes, but not exactly as described.  I adjusted the toroid with the
> xmitter connected to a dummy load, while listening to the signal on another
> receiver. Frankly, the signal sounded bad, as though it was being modulated,
> so I adjusted the toroid until I had a clean-sounding signal.  There is no
> doubt in my mind this is the reason the power is low.
>
> The question in my mind is whether or not the sound of the signal is
> indicative of not enough spur suppression or some artifact from too tight of
> a coupling between the receiver and transmitter when I was making the
> adjustment.
> (I had a
> receive wire laying across the coax going to the load during the test.)
> I'm
> thinking about borrowing the spec analyzer from work in a couple of days to
> look at the output while I try adjusting it again.  Could you remind me what
> the spec's are for harmonic suppression?  I can't remember them off-hand.
>
> Rick Hampton, WD8KEL