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

[Eric Fitzgerald]

On 7/18/23 2:30 AM, Jim Brown wrote:
> 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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