Ham Radio - truSDX transmitted audio and signal quality in SSB, AM, and FM. 

There's going to be a follow up vid looking for ways to not overdrive and clip on SSB.

I got one a few weeks ago. For what it is, it's amazing. Even to just take a "deep dive" on how it works and the math behind the signal processing it's worth the $150 or so it cost. I have a feeling the SSB problems are a result of the Amplitude (PWM) modulation and the Phase modulation being slightly out-of-sync with each other. SSB is the only mode where it has to both phase modulate and amplitude modulate at the same time. For CW and AM, it only has to amplitude modulate (via PWM) and for FM it only has to frequency modulate (by rapidly changing the frequency of the SI5351A). But for SSB it has to do both! If they are just a small bit out of sync with each other, you won't get a clean signal. Because the Si5351A is controlled by I2C data, getting it precisely timed with the PWM modulation will be a little tricky.

Both the onboard mic and speaker are emergency devices, add-on functions, the absolute minimum to get by on if needed. I think you can even use one of its buttons to send CW if you lack a key. Because assembled kits can be purchased from China, too many people seem to think this rig is a commercial appliance instead of a dirt cheap experimental rig. From tuning to interfaces to mic and speaker it's an experiment, a project radio. Yep, it works, and for the $60 in parts and ingenious software it's a many-mode multi-band rig that works pretty well and will serve a lot of poor hams around the world, giving them a chance to get on the air, and then embellish it as they learn and can get parts. But it's up to the hobbyist to make it work really well. That's the whole idea. We're hams, not CBers. We have a license to experiment, to do whatever we want with our radios, to design and build them from scratch, build a kit, or buy an appliance to plug into the wall and an antenna to plug into the back, our choice, it's up to us. We have a license to do it all. These rigs aren't appliances. They're projects. Hams have added variable voltage to their (tr)uSDX's to control output power, they tune the output toroids, they've added external speaker mics, even turned them into HT's - so far. That's just the beginning. I figure showing creative ways to solve problems and improve these little rigs are what the RU-vid videos are going to be about, and I'm surprised when I see them being reviewed, video after video as if they were Kenwood's or Yaesu's. They just aren't. They were never intended to be. These are for the people who dig into ham radio, not the super-CBers.

I bought the Pacific Antenna Electret Microphone kit fer $15 (1/2 to assemble) and it definitely improved the audio of my uSDX tx audio. 73/K6SDW

Very good as always Kevin.

I've got one of these to play with for when the snow flies and I can't go outside. Based on your video Kevin, I'm glad I also have an 891 as well. Thanks for your time. Glen

Its a fantastic concept in terms of showing what is possible with so few components and inovative way of generating SSB, AM and FM. Would be great if it was based on a cheap ARM MPU instead of the Atmel since these are much more powerful and have enough flash memory not to need to compromise on features.

Thanks for another informative the video. Love my (Tr)USDX, but i have received several poor audio quality reports on SSB described as "distortion" or "overmodulation". Without hearing or seeing your RX transmission it is difficult to determine if using a different mic or changing the mic gain settings offers much improvement. By the way, I also had good success using the MX-P50M(with mod) and Minipa70 amplifiers with the radio. Not for QRP work, but it can help punch through pile ups.

I appreciate your honesty on the review. BTW, I figured how to shut off Adblocker for your specific channel here. I forgot about the Adblocker thing, until you mentioned it on a previous video. Thank you for your educational videos. K1QS.

Excellent! There will always be a limitation to how good it can get with 8 bit processing but it would be nice to get it as good as we can. Really hard to know which steps help if you can't check the result. The best I have been able to do is to listen to myself over web sdr, usually sounds weak and not too clear but... it has been good enough to make contacts. It would be nice to make it better, so what you are doing is very good. Thanks!

Hi Kevin, looks like a fun radio! Hope to see you at Quartzfest. 73, Dave, KEØOG

I used an old wouxan mic and old small headset and also earbuds. I’ve made numerous contacts including 3 qso’s to russia. Worked great on my station hex beam as well as mpas2.

Interesting test. In any case, an improvement will be welcome if it comes, but after all, today's quality is absolutely acceptable. I recorded my real QSOs via sdr radio (you can listen to them on my RU-vid channel) and I assure you that even in contest it is fine.

I’ve made over 130 QSOs on mine, as far as 2000 miles, all on SSB or FT8 with CAT. Never had any complaints about audio quality on phone. Amazing little rig. Your splatter seems worse than the TinySA output I’ve seen would indicate. Hard to know what is normal as they are all hand built.

Thanks Kevin, great video! BTW I saw your previous movie recommendation, 'Nomadland' and really enjoyed it. Hey, I was wondering if you have had any luck with half square antennas? Those seem to be interesting since they have some gain - I was thinking it could make a good video. Keep up the good work, Kevin!

Thank you for sharing your test results. I just built one of these and it works fine except for SSB tx audio. I monitored the signal using another radio and no values for 3.2 Noise Gate or 3.3 TX drive provided adequate TX audio. I had several contacts tell me the audio was "scratchy". This plus the splatter as you pointed out, make me think it is overmodulating. Do you think a firmware change is needed or hardware? Thanks again, I always enjoy your videos.

Perhaps it was already said, but you were transmitting 4khz instead of 2.4khz. I would suggest trying that as well. Having said that, we can never expect this radio to produce the same signal quality as a more expensive rig. Thanks for this video, keep them coming as these type of content helps the rest of us to understand our rigs better! 73 de Luis, HB9HJU

Thanks, Kevin, this was helpful. Maybe you looked at CW in an earlier video, but I’m curious how it behaves there. It would be handy to have the voice modes, but CW is king.

That’s interesting. After this video, I tested mine on SSB. My audio seems just over 2KC wide, with no bleed over to the opposite sideband. I don’t have the same equipment as you to measure the signal, but used my FTDX101D while the (tr)uSDX was transmitting into a dummy load.

FM would be handy for working via gateways on 10m band :-) since my IC-756 has died I no longer have an HF set for /P operation, that wee beastie looks almost perfect! and would be so much easier to transport up into the hills around here, Ayrshire, S.W.Scotland. :-)

Can we have a video with this small radio receiving in AM and FM?

Can you check and verify truSDX receiver audio and signal sensitivity in SSB, AM, and FM ?

I’m not sure if 1.0 firmware has mic gain or AGC. But the 2.0 beta is abandoning AM/FM because it’s bad and rarely used. In its place, you get a spectrum, direct USB audio/CAT, and a few minor things. The stable release of 2.0 should be pretty good. But your audio sounds a lot like mine, using a similar method. The lower bands should also be significantly better, because it requires less processing from the chip. There’s only so much an 8-bit Arduino can fake in modulation.

Might also play around with the "transmit drive" menu 3.3, Manuel says 4 is the best compromise and if you turn it up you get more compression and at 1 it's very linear. But some times reasonable minds will differ...

I think you can improve you measurement (wanted signal strength compared to unwanted / suppression) by having max hold on the top power over frequency indikation. These shades of yellow are really hard to judge wrt level, and a signal 50dB down might light up yellow still.

I would like to see the results using a good mike

Will you be showing how to connect it up and use WSPR or FT8?

Good video and I have really enjoyed the way you have been mixing up content it has been a nice change of pace. Thanks for sharing. Vic de KE8JWE

This is helpful. Thanks! 72 - AA4K

The TruSDX does everything that a normal transceiver does using C++ for DSP.

Mine will be here in two days 😊

Thanks Kevin. My trusdx works great... except for the occasional shut off (I use it for CW only). I find that if I quickly unplug and replug the power source it operates again. But it's annoying if it happens in the middle of a qso. I am not up to the soldering you did. Are there possibly any other causes/remedies for the occasional shut off problem? Thanks, Scott

The thumbs-up counter was at 555 and I kind of wanted to leave it there for a moment ;-) I pushed it to 556 anyhow.

Wow, the transmit audio is severely low pass filtered. The high end is completely gone. I wonder if a better quality external mic would have the same issue. As it is, something like the diagnostic rhyme test (DRT) scores for intelligibility would be really bad.

I am still a tech only. Is this radio a kit? Thank you for demonstrating the audio quality. KJ6VYF Dave

I like to see the comparison with IC-705. Thank you. 73

I gotta be real with you, a good portion of that splatter may be a side effect of how you have your SDR software configured.

Hello, dear OM Kevin, you have to 'chanche' a view of your 'settings' in the menu, very, very carefully! Do it realy carefull, and sensitive, ... ! Step by step, not from 0 to 100 (255) in half a second, ... ! - Less is more with the (TR)_U_SDX ! - I made it that 'way' and my results are better then before, ... ! (From the 'standard values', the radio comes with, ...!) It is an 'experimental SDR-radio' in every word, that Manuel said. Each 'radio' will differ a little bit, (some more, some less) from radio to radio, on the hardware side. And then the software-part has to do the rest, and you, the 'user', has to do that very carefull! There is lot of work, for a simple 8-bit controller! Maybe, there are some glitches, we have to sail arround! Hopefully, only by 'gently chanche' some parameter in the menu! All together, the (small) hard-ware differences, and the new kind of SDR-software, to create a SSB-signal and demodulation, with the special kind in a new and 'different way', to buildt and use a 'Ham-radio'-TRX, will come together, and is 'not easy' to understand. Some differences (bad SSB modulation, too loud or too low 'mike-gain', or other things ...) will occure, when the radio is in use, from radio to radio! Most of the time, you can 're-adjust' some things, in the menu, and all will be 'right'. Maybe some 'things' are not that easy to get right, but Manuel and Guido will do the best they can do! I'm sure, that it is that way! Stay in 'tune' with Manuel on his HP and also on the forum, especialy made for the (TR)_U_SDX ! Look for any new details and hints, that will come in a regulary way, ... ! There are a many 'answers' to a lot of questions, that will come in the future, to find right now! I should say: RTFM, ... but it's a lot to look for, ... for a 'simple experimental radio', that this two guy's implement, in the last two years! It helps me a lot, during the 'bad times' in the 'Corona shut-down' periode, here in DL and I'm a proud 'user' of that 'special little QRP-radio' ! Please be aware that English is not my native tounge and when you find some mistakes in spelling and/or writing, please be so kind, 'collect' them carefull and recycle them in a 'professional' way, ... ! Thanks ! 73/72 de Markus ; db9pz (5 km/3 miles east of LX ; JN39FQ)

I guess it's not bad for a low cost transceiver.

Ugh. Ugly audio, Kevin.

I'm wondering if the SSB transmission sounds " not so well "' because of the finals in this radio. Is it not Claas-E, that is used ?