[Elecraft] K3 Harmonic Distortion

[K7TV]

Julian, G4ILO wrote:
>I think it was me who used the term "ghost" signals when referring to the
harmonically related CW traces >I could see on the CW Skimmer display.

Julian,

About 6 months ago I found a similar situation with another radio and
another program. In that case the distortion was definitely caused by the
sound card input being overdriven, not by the radio. I am not saying that
that is happening for you, only that it CAN happen with certain equipment. 

Here are the details if you want to know. I was building a new interface
that lets me operate PSK-31 and other modes (including pactor 2) with
switching between any of two radios and any two hardware modems and
soundcard. It is also designed to work with both my desktop computer and my
laptop (HP ZT-3000) by manually moving the cable. Serial port was switched
along with the modems. The radios were FT-1000D and TS-570, both interfaced
through the connector on the back. The 1000D (now sold to finance K3) has a
single fixed output level, the 570 three selectable levels. I selected the
level most closely matching the 1000D. The software was MixW running on the
HP laptop. I found that I could not only see a give station in two places,
but copy their PSK-31 in both places! The second frequency was outside
(above) the filter cutoff, but the signal was about as strong as the one in
the passband. I don't remember the actual frequencies, but there was a big
difference in them, such as double or triple. I didn't determine if the
ghost was created as a harmonic or by mixing, but it was good copy and
strong. (Hmmm,... wonder if PSK would be copiable on a harmonic?) My
interface has a volume control for the output (as well as input) of each
radio. When I turned down the output at the interface (not touching the
radio), the ghost went away.

On a tangent topic: I had previously run the 570 with the laptop using a
much simpler interface, and somewhat marginal results (did not run into any
ghost, was probably using a lower output level selected on the radio). That
interface had short audio cables. The new interface has long cables for
flexibility in placing the equipment around the shack. When I first tried to
transmit, there was a horrible hum on the signal. I had tied together the 3
grounds of the 570 at the aux connector. I solved the problem completely by
running separate 3 grounds from the 570 to the interface box with its
transformers. The 1000D had no such need, maybe because its PSU was
built-in) but I implemented both radio cables with separate grounds to be
prepared for future radios. I should be covered for the K3, whether it
behaves like a 1000D or like a 570. I wonder though if the K3 is more
similar to one or the other in its grounding scheme...

73,
Erik K7TV

KX-1
T-1
K3 on order
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