The (tr)uSDX QRP transceiver: My initial impressions after a CW POTA activation

I mentioned in a previous post that I placed an order for a (tr)uSDX kit with roWaves in February. My order was placed for a third production run kit and I assumed I would receive it sometime in March 2022.

Later that month, I discovered that DL2MAN announced AliExpress would sell both kits and fully-assembled versions of the (tr)uSDX. I used the link from DL2MAN’s website and ordered a fully-assembled unit.

My thinking was that I would receive the kit first, build it, then test the performance by comparing it with the factory-assembled unit. These units are so dang affordable I felt like I could splurge for both.

roWaves order on hold

I recently discovered that my (tr)uSDX kit had been placed on hold due to issues that popped up in the first and second kit group buys via roWaves.

Evidently–and someone can correct me if I’m wrong here–the first and second production runs kits had a component issue that equated to lower output power. In addition, Josh (KI6NAZ), reports that the early group orders had no boot loaded and the MCU was DOA.

I’ll patiently wait for roWaves to sort this out. I’m not in a huge hurry at this point because, frankly, my available time to build a kit has come and gone. The next few months, I’ve a lot of plans, travels, and projects to work through.

Fully-assembled (tr)uSDX

Much to my surprise, the assembled (tr)uSDX arrived Monday and I picked it up when I was at home on Tuesday of this week.

I was only home one night, but managed to do some quick testing.

I soldered Anderson Powerpole connectors on the supplied power cable pigtails. Next, I hooked the (tr)uSDX up to my variable power supply and a dummy load.

A quick test showed that I was getting about 3 watts of output power with about 13-13.2 volts, 3.25 watts at 13.8 volts, and 2 watts of power with 9-10 volts. This is lower than the expected 5 watts of output power @ 13.8 volts. The current consumption in receive however was about 60 mA even at 9 volts. That’s slightly below the published specs.

I honestly had no time that evening to play radio, but I took a moment to hook up the (tr)uSDX to my skyloop antenna just to check the audio quality in SSB.

As luck would have it, the first station I heard on 40 meters was a POTA activator in Ohio. He was calling CQ, so I couldn’t help but reply. I pressed the PTT button on the (tr)uSDX, spoke into the internal mic,  and he came back immediately with a 5×8 report. My meter was showing a max of 2 watts output power–the heavy lifting, of course, was done by the antenna.

This gave me a very good initial impression!

(tr)uSDX POTA Activation

The following morning, after running a few errands and carting my kids to some appointments, I left the QTH for a couple nights of travel.

I just couldn’t help but pack the (tr)uSDX and attempt a park activation en route. My goal was to see if it had enough positive receiver characteristics to be a proper POTA/SOTA portable rig–the feature set is comprehensive for a $135 radio.

I stopped by South Mountains State Park and paired the (tr)uSDX to an EFHW my buddy Steve (MW0SAW) kindly built and sent me. [Steve–I’m loving this antenna! Thanks again, OM!]

I made a video of the entire activation and will soon post the field report. I’ll push this video to the front of the line, but with my internet bandwidth, it might still be a few days before I can post it. Because of this, I thought I’d go ahead and share some of my experience with the (tr)uSDX in case you’ve been thinking of purchasing one.

(tr)uSDX pros

This little radio design has a lot going for it.

The chassis is very compact–perhaps the size of two Altoids tins stacked on top of each other. The encoder does protrude–in fact, it’s nearly as deep as the radio chassis. It’s not that the encoder is particularly tall, it’s just that the (tr)uSDX is so wee.

The radio has all of the CW adjustments you’d typically find in a compact field transceiver and even sports QSK (there’s also a semi QSK setting) with no relay noise. I assume it uses PIN diode switching.

(tr)uSDX Cons

Unfortunately, I did find a few negatives. The reviewer in me automatically gives the (tr)uSDX wide berth and a lot of forgiveness: we’re talking about a $135 transceiver here. I don’t think anyone is under the impression this would be a stellar performer.

In my opinion, the biggest negative is the (tr)uSDX audio. This little rig has a very high noise floor–perhaps S5 or S6.

The internal speaker is very modest and mine is incapable of producing audio at a level that is workable in the field where there are ambient noises like wind, water, conversations, birds, etc. The audio sounds decent when working a strong station, but weak stations are extremely hard to hear. If you turn up the volume on my unit beyond level 14, the audio simply squeals. I need to tinker with the volume control more.

Since the audio was so weak, I hooked up my Sony digital audio recorder to the (tr)uSDX headphone jack and made a separate audio recording for the upcoming activation video.

The headphone audio is louder, but there’s also a lot of noise in the audio amplification chain–again placing the (tr)uSDX noise floor around S5 or S6.

I was fully expecting the (tr)uSDX receiver to overload and it does. The variable filter helps and narrowing it makes the audio sound more pleasant in CW, but it doesn’t stop adjacent signals from bleeding through. Honestly, though? I could live with this and just use the filter between my ears if the audio was simply cleaner.

I also discovered that my unit needs alignment: the frequency display is off by 1.6 kHz in CW mode on 40 meters. I’ve put this on my to-do list–after all, this is a project radio meant for hands-on tweaking. I’m good with that.

One final point and minor quibble: the OLED display is very difficult to read outdoors. It’s superb indoors, but outside any sunlight or reflection simply wipes it out. To read the display I had to cover it with my hand.

The activation was a success: I worked 11 stations in 20 minutes or less, but I’m sure there were weaker signals out there I missed because they were simply buried in the (tr)uSDX’s noise floor.

I liked the (tr)uSDX keying, and I love the form factor, but I’m not sure I’ll ever use this radio again–configured as it is now–during an activation. For casual contacts, it could still be fun.

A little (tr)uSDX grace

I mean…$135 right?!?

The (tr)uSDX is an open source project and truly pushes the boundaries of what one can achieve for $135–again, even much less for the kit version. Frankly, I’m in absolute awe that any transceiver can be made below the $150 price point; especially a multiband, multimode transceiver.

The (tr)uSDX is an experimenter’s radio and I plan to dig into this little unit and see if there’s anything I can do to lower that noise floor. My hope is that the CPU or display may simply need better grounding or isolation. My time is limited at the moment, but I will open into this radio in the next few weeks.

In fact, eventually completing the kit build will give me an opportunity to explore the components and connections in much better detail.

I do know that my unit also seems to have the power output issue that some of the roWaves kits have. I can’t achieve anything better than 3.25 or 3.5 watts output at 13.8 volts. It should be about 5 watts at 13.8 V.

I would welcome your suggestions especially if you’ve built the (tr)uSDX kit or if you’ve put your assembled (tr)uSDX on the air and found that it had much better audio characteristics.

32 thoughts on “The (tr)uSDX QRP transceiver: My initial impressions after a CW POTA activation”

  1. Try to switch the display off, I have a same display in another kit and the display makes a lot of noise.
    Awaiting my truSDX from Spain… Maybe I’ll write a report about it.

    Chrz,
    Frank

    1. I’m really impressed with my trusdx. It came from Suni in China, one of DL2MAN’s recommended sources. It was prebuilt, and it works! I aligned the freq with my lab 599, and sensitivity was quite good on my Gap Titan. Audio was great with my Yamaha headphone/mic combo. That little speaker doesn’t do it Justice. I do need to fashion an adapter to get the mic on my headset working. Thanks DL2MAN and PE1NNZ

  2. Again an great report about a radio that is new to the market. I looked at this one, even of price is nice, not for me at present though. Thanks for the review.

  3. I have one of the uSDX rigs, the one that is 4d x 3w x 1h. Paid $115 on AliExpress fully assembled.

    I worked a few stations with it and did some bench testing.

    The rcvr was not so sensitivity, 1uV to hear a CW sig. Power output was over 4W on 80-40, but dropped off on the upper bands with about 2W on 10m. I had same issue with the volume, had to keep high to hear much.

    Test with 13.9VDC power supply into good dummy load. Measured with my R70 digital watt meter.
    80m 4.29W
    40m 3.9W
    30m 3.1W
    20m 3.46W
    18.1 MHz 2.0W
    15m 2.6W
    24 MHz 2.3W
    10m 2.3W

    Current draw
    Receive with no audio 0.12A
    Receive with full audio 0.47A
    Transmit with 3.8W output 0.73A

    It is a nice rig for the money, easy way to get into QRP. I recommend it for starters.

    73, ron, n9ee

    1. (Tr)uSDX only covers 80-60-40-30-20m
      So how did you test it above 20m!
      If you paid AliExpress 115usd then you were robbed, mine was £45.

      Also dispute your claimed Rx sensitivity

      You clearly were not reviewing a (tr)uSDX
      Dave MM0HVW

  4. Anxiously awaiting my order – sitting in US customs right now. Thanks for the initial review as it helps with my expectations.

    Now to exercise patience as I continue to wait….

  5. RE: freq display problem. This from the Facebook group:

    “As Dov already indicated, there is a function in the menu to set the reference frequency. The default (at least for mine) was 27.00000MHz. I determined that a signal that was supposed to be on 7.255MHz was actually received on 7.25555MHZ. So it was too high, and I had to reduce the reference frequency in menu item 8.3. I did the following calculation: 7.255 / 7.25555 to determine the factor that I needed to apply to the default reference frequency (in my case that was 0.9999242. I multiplied 27.000MHz with that and ended up with 26.99795MHz. After I adjusted the reference frequency in the menu, my radio was spot on.”

    Dov Pauzner:
    “Press MENU then with encoder choose Ref freq and push encoder button once. Than you can fix the shifted frequency.”

    Rob
    KB7PWJ

  6. I have an assembled unit ordered from RoWaves, anticipated ship date was on March 28. Haven’t received a confirmation of shipment yet, but I am looking forward to getting some hands-on time with it. Looks like an interesting addition to my KX2 and QCXMini. Maybe not one you would build a planned activity around but a nice “just in case” radio to keep handy for spur of the moment stuff.

  7. Nice Review!
    I have a new firmware and my TX audio is perfect. Also the RX noiselevel is gone and the audio out of it is a lot better.

    Last weekend I check 100% solar power without any battery on 5V emergency mode.
    Awesome feeling without battery !
    73 David
    https://youtu.be/YomT80uyhxg

  8. Awaiting delivery of a pre-built as time is limited. Will be interested in how it performs for SOTA.

    So far my best experience in terms of function over cost has been a QCX Mini, followed by the SW-3B. I suspect these both outclass the tr(u)SDX. But it will be fun finding out!

  9. I received mine from AliExpress last week. I could not be more happy with the quality of components received in the kit. Truly first class. I completed assembly this week and am highly anticipating jumping on the airwaves today.

  10. I have a prebuilt unit from the approved eBay vendor and a kit I built. Both are running 2.00h firmware and my output and efficiency on both are good. While the noise floor isn’t as good as my more expensive rigs I am seeing from S2-4 depending on the unit and which band. Generally it is between S2-3 with some nosier areas. The day I got the prebuilt unit I tried it in a pileup, but had to wait until it quieted down. He said I was just above the noise, but it was to Bosnia, from Illinois on
    SSB, just over 4,800 miles. I was using it with an OCFD that is 66 feet long on 20 meters. I am surprised by the features for the price and while the performance could be better I don’t expect a lot for the $75 I paid for the kit as part of a group buy. I also had a QSO with someone around 50 miles from here and he said my audio sounded good with the built-in microphone. Audio from the small speaker is okay, but I have to try some headphones to see how that works. Thanks for your review!

  11. I recently received one of these amazing little radios.

    QRM levels at my QTH are quite high, so it’s difficult for me to accurately gauge how sensitive the receiver is – but I have been happy with the performance, especially for the price.

    What I have noticed, is that when using the (tr)uSDX with headphones, the audio sounds much nicer from higher impedance headphones, e.g. if I use 80 ohm DT770 headphones, instead of <20 ohm earbuds/headphones.

    So if I was to guess, it seems like a lot of the noise/hiss is from the audio amp side of things, rather than RF side. I had a similar experience with the Belka DX: in a quiet room the audio "hiss" was a little distracting, but higher impedance headphones removed it entirely – and outdoors it was barely noticeable anyway.

    In the grand scheme of things, it's not a big issue for me – I'm just amazed at the cost versus capability of this tiny radio and I'm very thankful to DL2MAN & PE1NNZ for developing it.

    I've no doubt it will be further refined and developed over time, but for now – apart from being an enjoyable radio to play around with, it's also a great way for someone on a tight budget to get on HF. I wish it had been around when I was younger! 🙂

    BTW, regarding power output, Manuel/Dl2MAN has a video on tweaking the output power levels:

      1. No problem, I hope you’re able to get the (tr)uSDX working satisfactorily.

        Thanks to your blog and videos I am planning on getting out more and operating my radios – I had a remarkable experience with the Belka DX outdoors a few weeks back -hearing the 17M IARU CW beacons from Hong Kong, Israel, Kenya, New York, Venezuela – with just the attached telescopic whip. I could definitely get used to a low noise floor 🙂

        I can also blame you for the fact that a KX-2 will soon be on its way to Ireland!

        72,
        Dave

  12. Thomas.
    I now have my (tr)uSDX working — and its pretty good.
    In terms of Power output: on 13.8V between 4 and 5 watts on 20M and more on the lower bands. (A bit too much on 80M!)

    The poor audio quality is I think because there is some kind of acoustic resonance with certain caps and the internal speaker. This causes the acoustic feedback. 650Hz appears to be the critical frequency — right where the TX is operating!

    Higher impedance ear buds or an external active speaker solves this to some extent but you still can’t turn up the volume above ’12’ or things become unstable again.

    Despite these (small) issues I’ve worked the USA from SW France on 5 occasions over the past week on 3-4W of CW with no difficulty.
    I also operated in an EU SSB contest at the weekend just using the internal mic! I made 10 good contacts in short order on 40M and 20M — so the little rig is certainly working.

    I’ve not managed to get the micro USB to do anything but lock the radio up — so I need to research this a bit more.

    As my rig came from the approved supplier in China, its not supplied with a boot loader for future firmware updates — so I need to look into that. My firmware is v2.0h.

    I’ve also not found out what all the menu items do?
    ‘LPF Config’?
    ‘R-shunt’?

    My TX display doesn’t appear to work for SWR and the like even when its selected in the MENU. Its fine for S-meter on RX but nothing on TX

    So more to learn — but Its certainly coming with me on POTA and SOTA activations this year 🙂

    Keep the videos coming.

    73
    Bruce G4ABX
    @G4ABX

    1. Thank you for the feedback!
      The contacts you’ve made with the (tr)uSDX are most impressive! Like you, I wasn’t able to get the SWR functionalit to work.
      My kit from roWaves arrived this week. I’m hoping a boot loader is inside! In truth, though, I’m not sure when I’ll get it built. I’m coming into travel season and have other projects ahead of it now. I am looking forward to the build, though.
      Cheers,
      Thomas

      1. Hi Thomas.
        I’ve solved the ‘No TX indication on the meter’ issue.
        It only works if you have a ‘straight key’ selected in the MENU. Then it does what it says it should.

        For reference my rig is in the 71% to 75%+ efficiency region across the bands.

        Last evening I also substituted a headset – with 200 ohm impedance phones. The difference in RX performance was amazing! No ringing, no resonances and very comfortable listening level with the volume set at ‘9’

        Now I have to work out why the VOX operates like ‘full break-in’ switching back to RX every other word!

        Still, we had be warned that this rig is a Project not a finished article.

        Have fun
        73
        Bruce G4ABX

        1. Hmmm… Not sure if I have any in the shack unless my Heil Proset K2 is 200 ohms…I can’t confirm this in the specs.

          Or possibly the Sennheisers in my shack.

          What brand are you using?

    2. LPF Config should be Lo as that is the filters the units currently come with. For future there will be 2 other options, but the filter values have not been worked out yet. R-shunt allows you to change the value of the track used as a shunt as apparently some boards could be a little out of spec from the 17 milliohms. This allows the efficiency meter to read more accurately.

  13. Question. I’m considering picking up one of these little transceivers. Is it possible to run this radio with an external mic? It looks like it has a mic output, but I can’t find any additional info. If so, what mic would work?

    1. Yes you can use an external mic — but be careful you don’t overdrive the audio chain. Keep the TX gain down to 2 or so.

      I bought an inexpensive speaker mic — and it works very well.]
      This is what I use for SOTA

      73
      Bruce G4ABX

        1. Ah. I thought someone might ask that!

          It’s a generic Speaker Mic I bought off ebay years ago for a few £’s. It had a TRRS plug on the end which I cut off and soldered on 2 TRS tails so I could mate all the functions with the trUSDX.
          The only thing I could confirm is that it has a 16 ohm speaker inside.
          The Mic handles PTT, Mic input and Speaker output so interfaces well with the little rig.

          I do want to reiterate that whatever external mic you use, listen to the rig’s audio on another RX and adjust the TX gain (Menu item) until its sounds OK. When I first connected the mic and listened, the signal sounded terrible with the ‘stock’ setting of ‘4’ I had to reduce this to ‘2’ to get acceptable audio quality.

          This is a really simple TX chain so don’t expect ‘K3’ quality but for its intended purpose, it’s an amazing little rig.

          Best DX on ‘5 watts’ to the ‘QRP-GUYS ‘ 3-band vertical SSB, is Finland from SW France.
          On CW I regularly work the East coast of the USA

          73
          Bruce G4ABX

  14. How do get out of all the menus once you have finished the settings? Has me stymied!

    Thanks!

    72, Rick , WB3BIQ

    1. Rick
      There are several ways to get out of the MENU.
      Push the MENU button twice or push the ENTER button twice and you should be back to operating on your original frequency etc.
      73
      Bruce G4ABX

Leave a Reply

Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.