Wiring phone to KX2 for Sotamat

[NN6RF]

Hi there,
Looking to find out a way to wire up my KX2 to my phone to use Sotamat. I had purchased a USB-C to TRRS jack then a TRRS cable to a Mic/Headphone breakout cable as pictured, but this does not work or at least does not work with my current settings. Am I not providing the correct settings or need to enable/disable something in the menu?

[WU7H]

https://sotamat.com/sotacat/

[NN6RF]

I did order components and ordered up some boards on Osh from K5EM’s design but hoping to hit a summit this weekend and wanted to know if I could kludge something together before then.

[WU7H]

Every time I’ve used it, I just hold the phone speaker up to the internal KX2 mic and it works 100%.

[F4LEK]

I agree.

• Set the radio to the FT8 frequency.
• Select your summit in the sotamat app.
• Hold the phone close to the mic, key the radio and press play in the app (it will play the spot three times).

Done. No cables, nothing required.

[AB6D]

Three thoughts:

1. I agree with WU7H and F4LEK: just using the phone-speaker into the KX2-microphone is what 98% of us do.
   The trick is to “calibrate” the speaker volume and speaker distance so that you do not apply ALC, but get as close to engaging ALC as possible. In other words, don’t over-drive the microphone and don’t cause distortion. On a KX2 / KX3, when you have the “ALC” bar graph displayed, any number of bars less than 5 bars means “you are approaching ALC, but you have not yet engaged ALC”. Any reading of 5 bars or more means “you are applying ALC, which is non-linear amplification, which is creating distortion.”
   Doing this will create the best signal-to-noise radio (the best FT8 signal from the speaker in relation to the wind and birds chirping in the background), with the least ALC distortion.
   There is a video showing this calibration: (scrub to the part in the field) https://youtu.be/eBgVnuC_bSg?si=mrAeg6xL8iwBmZcO

2. If you really must use a cable, you are going to have to mess around with a lot of settings: VOX, VOX delay, MIC BTN, VOX level, VOX enable/disable, etc. This is a pain in the field. And then you will forget to turn one of those settings back and be very confused in the thin air at 13,000 feet. However, when I started with SOTAMAT I too thought that getting a good signal would require a cable, so I made a video of the steps: Elecraft Radio Setup for Beginners using SOTAmat
   There is a common mistake made when using a cable: the cell phone thinks it is the “source” and that the device plugged in is a “sink” (like headphones). The Elecraft radio thinks it is the “source” and that the device plugged in is a “sink”. Thus you need to cross the inputs and outputs between them so the output of one becomes the input to the other. Normal cables don’t do that! I build my own and the wiring diagram is on the FAQ page of https://sotamat.com

3. You get the best of all worlds if you use a SOTACAT as WU7H suggested: it doesn’t use audio and has the KX2/KX3 directly synthesize the FT8 signals. There is a professionally built product version from @K5EM you can buy, or you can build your own from the open source docs (it is a fun hour+ build).

73 de AB6D - Brian

[KO4YLZ]

Ditto. Hold phone away from KXz2 mic so you have 3 bars on ALC meter

[NN6RF]

Thanks all, I did what was recommended today and just held it near the mic and it worked well. I do have parts on the way and a few PCBs from OSH for the sotacat K5EM designed so will be doing that whenever OSH completes them.

[AL5KA]

Reviving an old thread - I’m trying FT8 for the first time. I watched your video and am doing a similar set up, but it only seems to work with a MIC setting of 1, anything above that and the radio is transmitting even when it should be listening. Any ideas?

[WU7H]

Thanks for the 20m cw QSO the other day.

In this thread we were specifically talking about using SOTAMAT for spotting, not doing general FT8. When you spot with SOTAMAT there is no listening, you are just blasting out some FT8.

I don’t think using ‘acoustic coupling’ for general FT8 is viable. I would look in to some sort of interface like a Digirig. Ideally something that has isolation so you don’t fry your phone with RF!

I listened for you on FT8 the other day but didn’t decode you. I was able to get you pretty easily on 20 cw. The problem with FT8 is that everyone is crammed close together, and a lot of those stations are running some power. You are essentially trying to whisper something to me at a football game =)

On 20m cw you are whispering, but we are in a quiet room together.

73,

-Josh WU7H

[AL5KA]

Thank you so much for the QSO! You have no idea how much those mean to me, I really struggle to make contacts, and I believe I have contacted you more than once now. Additionally, thank you for putting up with my slow and shoddy morse code

Re: FT8, I am using the same set up as AB6D except I’m using the iFTX app instead of SOTAMAT. Should have clarified that. I did have my bandwidth set too small, next time I will adjust that and hopefully have better results. Still don’t understand why it only seems to work with a MIC setting of 1, though

[AB6D]

• When you say you have a “mic setting of 1”, are you using cables between the phone and the radio or are you playing the audio from the phone’s speaker into the radio’s microphone?
• Is it a KX2 radio?
• When you say “a mic setting of 1” do you mean the radio’s “mic gain” setting is 1?

A “mic setting of 1” only makes sense if you had audio cables connecting the phone to the radio and if the phone’s volume was set medium-to-high.