[Elecraft] KX1 keying and audio artifacts vs. K1

[Wayne Burdick]

I've had a few questions on the topic of audio keying artifacts from prospective
KX1 builders.

The KX1 is nearly identical in its keying and audio characteristics to the K1.
Both use audio-derived AGC and simple muting circuitry, and thus exhibit very
slight keying artifacts. These are unavoidable without the addition of a lot
more components in the audio stages. But as the rig's designer and first
extensive user, I tried to minimize parts count (so it would fit in the box and
be easy to build) while making it pleasant to use.

There are certain conditions that can make things worse. The most obvious is
your choice of headphones. If they have a lot of bass (low-pitch sentivity),
you'll hear more artifacts. The effect can be lessened by using 12 to 18 k at
R32 rather than 22 k. This resistor is on the bottom of the board and is
relatively easy to change--you can even try paralleling other resistors to
determine the ideal value.

Other factors that contribute to keying artifacts are listed below, with
possible ways to reduce them. All of this advice applies equally to the K1 and
similar rigs.

1. Band noise

  If you have very strong QRN or QRM on frequency, reducing the RF GAIN can help.

2. Filter bandwidth 

  Tigtening the filter during CW use can also help. Experiment with different settings.

3. Battery voltage 

  If the battery voltage drops too low, the voltage regulators' output voltage
can drop, inducing current or voltage spikes into low-level stages. Recharge or
replace the batteries in this case.

4. High SWR

  This can cause RFI or ground loops that may cause clicks or thumps. In some
cases RF can couple directly into the headphone cable; keep it away from the
antenna. Improving your SWR, adding more ground radials, or using a balun may
also help.

5. Excessive transmit current

  This can also cause ground loops, or impulses fed back from the DC supply into
low-level stages. The usual reason for excessive current is working into a very
low-Z load; check your SWR. High current can also lead to a drop in battery
voltage (see above).

73,
Wayne
N6KR


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