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.
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