[Elecraft] Very late to the party - computer rig control and sound card modes for K3

[Jim Brown]

Hi Paul,

Yes, that USB cable will work just fine for rig control. You will want 
some sort of audio interface. The Signalink is well advertised, but not 
a great product nor value for the money. There's a piece on my website 
about some very good interfaces from the world of pro audio. Some of the 
recommended products are getting a bit old in the tooth, but I would buy 
used on ebay from vendors having nearly 100% ratings. The most you might 
need to do is solder up a few cables with 3.5mm and RCA connectors. The 
link also provides several good ways to set levels, depending the 
instrumentation that you have on hand, including your ears. 
http://k9yc.com/USB_Interfaces.pdf

Go to the WSJT-X download site, get the software and install it, and 
STUDY the documentation that's on the website, and that downloads with 
the program. All of the digital modes generate audio tones that modulate 
a USB transmitter, transmitting a signal that's about 50 Hz wide, at an 
RF frequency equal to the audio frequency plus the dial frequency. In 
other words, it occupies a specific spot on the dial, just like a CW 
signal, except that it's frequency shifted for modulation.

Carefully follow the instructions in the K3 manual for setting audio 
drive, which calls for the ALC to show 4 bars flashing 5. You should be 
in DATA A mode, and driving the Line Input. Follow instructions in the 
Elecraft manual for what knob to turn to adjust levels.

For decoding, the Line Out drives the computer sound card Recording 
Input. The sound card MUST be set in Windows for 48 kHz STEREO. Windows 
has a nasty habit of changing this when it does program updates.

I use VOX for PTT, so you'll need to fiddle with VOX gain, which 
interacts with audio input drive.

WSJT-X does a St. Vitus dance to prevent harmonic distortion being 
transmitted by a technique it CALLS "Split" (not what experienced hams 
would call split for working DX) that shifts the TX frequency in one 
direction and the AF in the other so that any 2nd harmonic generated by 
overdrive is killed by the TX sideband filter.

In the WSJT-X instructions, you see directions to set the radio for 3 
kHz bandwidth and let the software do the filtering to separate signals 
in that passband. It's VERY good at that. On the spectrum and waterfal 
display of the audio passband, set it to start at 200 Hz and use a 
number of bins to make the upper limit about 3 kHz.

I have a very important difference with their instructions about setting 
the audio drive from the radio to the decoder. They say to set it for 30 
dB with no signal. That is VERY limiting of dynamic range, and will 
cause it to miss weak signals in the presence of very strong ones. My 
advice is to set audio drive so that the green bar on the left side 
comes as close as possible to 80 dB without ever turning red (which 
indicates digital clip).

In case you don't know, the AFSK mode is only for RTTY, which is 
transmitted LSB, while all other digital modes are transmitted USB, as 
I've described.

73, Jim K9YC

On 7/18/2023 1:58 AM, Paul Barlow wrote:
> Dear Elecrafters,
> 
> I am very late to the party. For various reasons I have been QRT for a few years and I'm just now getting back on the air. I'm still using a paper log, and QRP CW is my 'thing'.
> 
> My rig is a K3, serial no. in the 7000's. I have the KUSB cable, which I have only used to update the firmware. Could I use this to connect to a pc and have rig control via this cable? Say for interfacing with a logging program?
> 
> Also, I've never used the FT8 type modes. I understand they use the pc for all the signal processing, and I could interface the K3 directly using audio cables and VOX. I see that there are products available like the SignaLink which interface with a pc using usb, which I think might be a less fiddly option.