[Elecraft] HW-40 based amp, Class C PAs in general.

[Ron D' Eau Claire]

Kevin wrote:

> Class C amplifiers can be used as the final stage in a CW rig,
> but should NOT be used as "boots" for a CW rig.   When
> designed into the rig, provisions are made to control the
> rise and fall times of the keying waveform of the PA, eliminating
> key clicks.  If used after, say, a K1/K2, the non-linearity of the
> PA will alter the Kn's carefully shaped keying waveform, and
> generation of key clicks is extremely likely.  The station you are
> QSOing with will not report a problem, but your clicks will
> be heard up and down the band for many KHz.  This is IMD,
> not harmonics. It is to CW what splatter is to SSB, and the cause
> is exactly the same.

Very true, and a good reason to listen off of the sides of any signal when
giving a report. Whenever someone tells me he/she is running a "new" rig I
do a tune up and down from our frequency with a narrow filter looking for
clicks - especially if their signal is strong.

In this case, a self-described "appliance operator" was asking how to simply
use a K2 with his DX-40. I suggested that he use the K2 as a "VFO", with a
suitable attenuator between the K2 and the DX-40 VFO input and provide the
necessary switching to connect the antenna directly to the K2 for receiving.
That way he'd key the DX-40 as it was designed to be keyed.

As others have pointed out, the DX-40 does NOT meet current FCC regulations
for harmonic suppression for NEW equipment. However, older gear such as this
is 'grandfathered' and quite legal. It is possible that an outboard "low
pass" filter may be needed to avoid TVI on some bands depending upon the
signal strength of the TV signals in the area. Also, as others pointed out,
the K2 can not be used for SSB. The DX-40 is strictly a CW rig, and would
require a ground-up redesign for SSB service.

Ron AC7AC
K2 # 1289