Early days with the Chinese uSDR / uSDX reveals weaknesses

A couple days ago I finally took delivery of the uSDX/uSDR transceiver I ordered in late October from this seller on eBay. I’ve been tinkering with it in the shack since then and have started to form some initial impressions.

The uSDX is a super cheap transceiver and, to be clear, my expectations were (spoiler: thankfully) very low.

If you’ve been here for long, you’ll know that I don’t normally test or review super cheap transceiver varieties found on eBay, AliExpress, etc. So many people asked me to check out the uSDX, however, that I decided I would try to give it a shake out.

I’ve yet to take this little radio to the field, but I have made a couple dozen contacts from the shack, all in CW and I’ve done a lot of listening. Yesterday afternoon, I even hooked it up to an oscilloscope.

It’s still early days and I’m sharing the following observations and notes with the hope that uSDX owners might be able to guide me if I need to make menu adjustments to sort out a few issues.

More specifically, there are two big cons with my uSDX:

Con #1: The Audio

Trying to be diplomatic and kind with my words here, but let’s just say the uSDX audio leaves much to be desired.

I think it’s great this little transceiver has a built-in top-mounted speaker, but it produces some of the harshest, most spluttery audio I’ve ever heard in a radio.

On top of this, the volume control (which requires going into an embedded menu item to adjust) is just…strange. It’s hard to explain, but the audio feedback isn’t what I would expect from a volume control or AF gain. It seems like each volume control step (starting at “-1” and going up to “+16”) is a mix of both AF and RF gain values. It doesn’t have a fluid amplification progression like I would normally expect.

In fact, I can’t really turn the volume up to +16 because on many bands around level +14 or +15, it starts to emit a really loud squeal.

Although very minor compared with the issues above, the audio amplification chain also has an ever-present hiss.

In addition, even with the volume turned to “-1” I can still hear splattering and even garbled whispers of CW signals if connected to an antenna.

I hope I’m missing something here and the audio can be tailored for better listening. Perhaps there’s a combination of adjustments I can make in the menu options to help?

Please comment if you own a uSDX and can provide some feedback.

Con #2: The Receiver

Again, unless there’s a magic combination of adjustments I can make in menu items, I find the receiver of the uSDX to be incredibly anemic.

I took the uSDX to my buddy Vlado (N3CZ) yesterday and we hooked it up to an analog oscilloscope and signal generator.

We concluded that the uSDX is very sensitive, but the front end seems to be as wide open as a barn door.

This confirmed my on-the-air observations made over the past two days: even with the 500 Hz DSP filter engaged, CW signals as far away as +1.7 kHz could easily bleed through. In fact, quite often when I tune to a POTA or SOTA station operating CW, I could even hear FT8/FT4 stations bleeding through from far across the band.

I couldn’t help but think if I had taken the uSDX on my recent Mt Mitchell SOTA activation instead of the QRP Labs QCX-Mini, there’s no possible way I could have handled the pileup. The uSDX receiver would have completely fallen apart because it shows no ability to handle tightly spaced signals.

Again, if you’re a uSDX owner and can provide some insight here, I would very much appreciate it.

Still testing the uSDX TX

One of my main goals with purchasing the uSDX was to test the transmit signal to see how clean it might be and if there were spurs in any harmonics.

Vlado hooked up the uSDX to his oscilloscope and we discovered that it did produce spurious emissions in harmonics of the 40M band. The spurs were negligible and we both assume it might possibly be within FCC guidelines.

With that said, Vlado didn’t completely trust this particular analog oscilloscope because there appeared to be a slight fault in its BNC input port. We ran enough tests–and even compared the uSDX to my KX2–to know that there are definitely faint spurious emissions and that the CW transmit signal isn’t nearly as clean as the KX2.

Here’s a 2 second video clip showing the uSDX transmitting CW on 7 MHz into the scope:

Click here to view on Vimeo.

I plan to hook the uSDX to a digital oscilloscope to get more accurate results in the near future.

Not all cons

The uSDX does have some positive attributes.

For example, the QSK is quiet and even full break-in. This little radio is also chock-full of features. I’ve even found that though it’s advertised as an 8 band radio, mine will transmit on 10 bands; everything from 160-10 meters.

I think if I planned to operate the uSDX on SSB when the bands were relatively quiet, it might do quite well for casual contacts.

Time will tell…

To be clear, though, the issues above can be deal-killers for me.

I want my transmitted signal to be clean enough to at least meet FCC requirements–I like being a good neighbor on the bands.  This might require some modifications on the output, but let’s see what a digital oscilloscope might reveal.

Of course, if the uSDX can’t handle multiple CW signals being thrown at me at once, I can’t see how this would possibly work as a SOTA or POTA field radio.

I can already tell that the ergonomics of the particular uSDX model I purchased will likely lead to–as Spock put it in Star Trek IV–some “colorful metaphors.”  Especially when I reach for the volume control buried behind a menu item. (I mean, seriously?)

Again, if you own a similar uSDX, I’d love to hear your comments and suggestions!

48 thoughts on “Early days with the Chinese uSDR / uSDX reveals weaknesses”

  1. Your blog and Youtube channel is stellar and a boon to the ham radio community. Thanks for this review, I was looking at this radio but I’m far more interested in the Mountain Topper at this point. 73 de AI5DD

    1. Yeah, we covered this in a previous post. Not all of the Chinese uSDRs have dirty TX. Readers have sent me some reports with quite good purity and well within FCC requirements. That said, quality control is all but absent. I’d be willing to bet that the majority of these transceivers on the market are not compliant–that is a guess, though.

  2. Not that this will make it a better radio hahaha, but on mine I have found it you push in on the encoder, then turn it, you can adjust the volume that way.

  3. Hi Tom – I stand to be corrected with regard to my understanding of the uSDR/uSDX issue, but I believe the uSDR is a Chinese designed-down-to-a-price version of the original uSDX designed-up-to-a-spec transceiver developed by DL2MAN and others. From what I have seen, the uSDR doesn’t have a very good reputation whereas the original uSDX performs quite well. I guess it might be a case of “Caveat emptor.” Regards, Keith G0RQQ/VA2QU

    1. You’re right, Keith. In fact, just to make it clearer about the model I have, I altered the title of this post. It’s my understanding the original kit/homebew design is far superior. Hans Summers noted this much in a recent post.

  4. I guess you get what you pay for. For a few dollars more, you can get something that may be a little more polished. A Xeigu G1M or a G90 (used) comes to mind. I have the G90 and it’s a great little radio.

  5. I have the uSDX version, the 4″d x 3″w x 1″h version.

    The test gear is an IFR 1200S service monitor, not just a scope and sig gen. Has dev/rcv signal monitor and also a watt meter although not so accurate on HF.

    I wish you had performed test like rcv sensitivity. I found my uSDX to be somewhat weak on rcv, 1uV sen on all bands. Power out was 5W on 80 & 40m, but dropped off in the upper bands, about 2.4W on 10m. Might consider doing these test for tells what the rig can do. My uSDX did have good selectivity, near by stations did not bother me. But the rcv spkr audio is not so good, distorts often also.

    There are a number of designs for these rigs, mostly copied from others. They are inexpensive way of getting into QRP, they can work. There is also a FB page and many users are building their own, ordering the boards and parts and assembling. They do have a good following.

    My uSDX cost about $115 on AliExpress. Some on ebay want $160 so look around if interested. But these rigs are in no way replacement for FT818 or KX2/3 or IC705, etc. But can be useful for portable QRP.

    73, ron, n9ee/r

    1. Hi, Ron,

      I haven’t finished checking this little radio. We limited our tests yesterday knowing that the faulty BNC might give us incorrect results. We simply used the comparisons with the KX2 to know that TX wasn’t very clean.

      There’ll be more to come in due time!


      1. Thomas …. great review and I concur on your findings. I just received the other (older) version out of China without a battery inside and it behaves the same.

        I have gotten in on the last sandwich version order from DL2MAN. Are you interested in building your own from this source?

        73, phil KF6IF

      1. They’re probably trying to save on customs fees which are charged as I understand it on just the purchase price. If they charge $250 for shipping, can’t charge duty on this. Probably legal reasons for doing that. I think it’s “bass akwards” too 🙂

  6. Thank you for taking one for the team and verifying what we all suspected (but didn’t want to believe)… that with China and copies/clones are always “You get what you pay for”, caveat emptor, and so forth.
    I do hope for a 3 to 5 band, 5 to 10 watt, bluetooth enabled QRP rig, maybe with a spot for a couple 18650’s or just leave that external… but a decently low price radio that is set up for digital modes right out of the box, controlled via Windows, Android or iOS. With keyer port of course, but I think it’d be neat to throw a wire up in a tree, sit in a hammock with a small tablet, and have some keyboard QSO’s. The bluetooth could even be used for a small handheld PTT speaker/mic on SSB. Fun!

    1. Some of the radios out of China aren’t too bad. I’m not sure who all is involved in making radios over there but I have noticed quite a variety when it comes to quality. Can’t comment on the one in this article yet as I just ordered it and have not recieved it yet. I’ll bet it works a lot better using it with a computer than stand alone though. I look forward to finding out. I have NEVER checked out Software Defined Radio before. It will be interesting.

  7. Hi there,
    Well, I did warn you. I think I was lucky to get my money back. If you think CW is bad, wait until you try SSB.

    I was inaudible on the internal microphone and none of the four ‘compatible’ microphones, were….! No TX or no audio. It seems everyone who sells one, makes it slightly different, which particularly included the wiring of the mike jack.

    Spectral purity? you must be having a laugh. Zero support from any of the ‘vendors’. Basically it’s e-waste, disguised as a radio.

    And I thought the Xeigu radios were cheap and nasty.

  8. The whole USDR USDX seems to be plagued with gross problems. The project in constantly being re-engineered to solve minor and major problems. Even the Groupe can not seem to agree on best practices. The original project was a collection of small component boards connected together. These boards being the best circuits available. Documentation, politely sucks. The whole project is in flux. The general agreement is experiment until you are satisfied with it’s operation or give up. When the Chinese reverse engineered clones showed up on the market, real chaos ensued. There are two basic versions, a sandwich, and flat conventional style radio. Both are trying for the same operating parameters. The basic project is trying to do too much with too few components. Basically trying to software control a direct conversion transceiver and make it multiband.

    This is not a radio to take to the field. When ever you want to make an adjustment you have to go to a menu. Some adjustments interact with other settings.

    I could see this radio being used in a clandestine operation on one preferred band and frequency by a spy perhaps. But forget any type of crowded band contest conditions where you are chasing stations on other bands and frequencies the encoder used is clunky with deep indents. You either dial a band change or go to a menu. Power out decreases as frequency increases, by about 50%.

    There does not seem to be any place to go for help or menu setting suggestions.

    If you are willing to live with this chaos and prepared to make modifications and software changes you could/might have a good time. Without going into specifics all my qrp single band radios outperform this radio. If you are new to qrp or considering a project direct conversion transceiver, I would recommend the the Pixie, from the Pixie Shop. Build it and modify and add to it. It can be modified for other bands and multi frequencies.

    As in all radio aspects, there are many willing to disagree with me, but these are my opinions and comments.

  9. I ordered one of the smaller version ones over E-Bay. I wanted the physically smaller one without an internal battery. My goal
    is a very light and very small rig for cw qrp SOTA.
    When it arrived I found it would not receive at all. I returned it
    I am waiting for it to be replaced.
    So I can’t yet judge what it is capable of — I hope it will work.
    I’m not expecting perfection .

  10. Thomas,
    I have one that I got from Banggood
    This has worked well, for what it is so far. I have only used it single sideband, and did a POTA activation with it. Mostly good signal reports and audio reports.
    I will say it is worthless for anything but 80 – 20 meters (although 20 is less than efficient compared to 80 and 40).
    There are SO many clones of clones of this and the other uSDX type (without the battery) that you are never sure what you are getting.
    I liked that banggood has a manual, which is a good thing. Perhaps that can help you as well.

    Overall, I have had a blast playing with this. I carry it everywhere and and when I am waiting form my son while chauffering him around, up comes the Telescopic whip and the wolf river coil on a mag mount on the truck, and I am hunting Parks. 🙂 I have made contacts on the internal battery at 5 watts or less on ssb as far away as Puerto Rico and Newfoundland with a 17 ft. telescopic whip on 20 meters and on 40 I hit Texas from Pennsylvania with a Sotabeam linked dipole on a 7m Tactical Mast.

    One note my volume only goes to 12. Weird.

    So the moral of the story. Buying one of there is russian roulette based on your seller and the manufacturer they contract with. I have put my name in for a real uSDX kit when they are released in the US, and I will let you know how that goes!

    I have been in contact with youtuber QRPLifeStyle who will be getting one of the German kits around Christmas and he will be recording a review about that timeframe. He has reviewed this and had some success with it as well.

    He shared his with Manuel DL2MAN who is one of the founders of the open source project who did a video on tests of this model (or one of the many that look the same but are different under the hood).

    73 and keep those videos coming!

  11. Hi Thomas,

    Thank you for sharing on this interesting and divisive topic.

    I’m sure there are many hams interested in this transceiver that don’t have the ability or time to make one from the original kit.

    I have been looking for a cheap travel transceiver for a while. So for now I have decided to order a G1M and continue to follow threads like these about the usdx.
    Keep up the good work. I love following your site and your reports.


  12. Thomas
    Greg here WA3GM. I have the uSDX line yours
    I have done 4 activations with this rig so far with about 90 cw contacts.
    The front end is horrible. As you stay I can hear stations a couple KC away.
    You can turn the volume up and down without being in the manual or at least you can on mine. Push down on the big black knob and then you can turn to the left or right to adjust the volume without being in the menu again at least that’s what you can do on mine.
    On my last activation the radio actually went deaf. It was a good thing I had a spare radio with me to finish up the activation.
    On a scale of 1 to 10 this gets maybe at two.
    I read also that those who produced as radio actually did so from an open source document that was not meant or intended for someone to make a profit.
    I am in the process of trying to return it right now for another unit or a refund but the process is slow so I’m not holding out too much hope.
    Again we get what we pay for and what we have here is about $170 radio that probably doesn’t have a third of that value in parts.
    Buyer beware as usual

    Thanks for all the great videos you put up and always good to work you when I can
    Greg WA3GM

  13. Thomas,

    Just a quick comment about this: “On top of this, the volume control (which requires going into an embedded menu item to adjust) is just…strange.”

    You can push the encoder knob in and then turn it to adjust volume without the hassle of dropping into a menu item.

    phil KF6IF

    1. Thanks for this tip, my radio has the same function… has anyone put together a list of suggested settings. I have not been able to confirm my radio can make SSB contacts. Maybe we need to put together a help group… TNX

  14. I have a copy of a manual for the USDX USDX version 1. This is the flat version. It is a 2.1 megabytes PDF. It’s in plain English language. Some of the abbreviations will leave you wondering but it does label all the menu setting and a few suggested settings and the hidden multifunction button pushing results, like the volume control. It is a starting point for those that did not get any documented information with their radios.. Does any one have a place to park this document so anyone can access it. My email is good in QRZ. Maybe together we can fill in the blanks. I now have mine working in cw well enough for to make contacts. I would be willing to reply with a PDF attached to anyone in need. 73 NL7QT

    1. Would love to have a copy of that manual. Finding out by trial and error but a few more things need clarifying like IQ Phase and reference frequency. adjusting the PA bias min and max are quite important as I found out. and the TX drive works best on mine at 3 with clean and clear audio reported. Checked in on the local net this morning and all glowing comments so quite happy here !! Yes the power goes down as freq goes up but hey its a qrp rig ! Trying to set it up on FT8 but not enough info……

    2. Hi Don,
      I have one without a manual and would welcome the chance to have a copy. I will be checking mine for the missing resistor at the side of the CPU and will try to make the radio work in a reasonable manner.
      73 Stephen G0FFB

  15. HI Thomas.
    This is Nick YO4LHR.
    Your comments are very good. I received something like this for a week https://m.banggood.com/USDR-uSDX-10-or-15-or-17-or-20-or-30-or-40-or-60- or-80m-8-Band-SDR-All-Mode-HF-SSB-QRP-Transceiver-Compatible-with-USDX-QCX-SSB-p-1911862.html? rmmds = orderdetail. (In fact, from 160 to 6m).
    Without high expectations for only $ 125. As someone said above, it’s like Russian roulette. I was lucky.
    Best 73 of all and HNY2022

  16. I’ve been through two of these “controls on top” models. The first had all the faults you mention. Crappy, squealy audio, ratty RF handling. Transmitter, well, that’n I didn’t have a way of getting too critical. Had a couple QSOs and that was it.
    . . . Main fault I found was the AF amp (LM386) is being overdriven. I lowered the value of R53, which helped considerably. Then I sold it for about half of what it cost me.
    . . . While later, like an idiot, I bought another one. That one had a better sounding audio but I still modified it: replaced R53 with a 1k edge-mount pot, modified the case to allow access to the pot and suddenly I had a decent receiver. Transmitter I still don’t have test equipment to check but I did have a couple Qs with it. One to Europe even.

    That said, it’s outrageiously is obvious — not only in this case but in the case of two other “variants” of these Chinese uSDX rigs — that quality varies from unit to unit and even more between the different designs/offerings on eBay & elsewhere. You get one of these, it’s the luck of the draw that you get a radio that works and even then you’ll have to modify it. Some come with recent versions of the software. Others are pretty much primordial.
    . . . They are toy radios, plain and simple. Ok for those who don’t want much more than a glorified — and barely functional — PM2 from the 1970s, but not a serious radio you’d take to the field without a backup X5105 😉

  17. I must be lucky. The spectral purity on the one I have is pretty decent, at least using the test equipment I have available (the TinySA & tons of attenuation).
    . . . But you are right about the audio. It can really suck. I tore into mine and installed a small edge-mount pot just above the headphone jack. Runs in the place of one of the resistors leading to the LM386 AF amp. Greatly changes how the radio sounds. I can run the menu AF gain at about 12 and control what I hear with the physical pot volume control.
    . . . Not a super radio outright but for what is at heart a fancy direct conversion receiver & transmitter, it’s not too bad. Deff good enough for me to use on a POTA run when the weather improves and stabilizes. 73 & tnx for the review || de W8IJN

  18. you must have realistic expectations when buying one of these ripoff clones of PE1NNZ’s uSDX transceiver project (found on github, which also is the best source of technical info and documentation):

    1. there are many variants of good to poor quality
    2. you must tailor your receive audio using various settings, but it will still only be fair
    (tip: use headphones, as the built-in speaker, which can work in a pinch, is not the best)
    3. you will experience key- and encoder clicks
    4. this is a sub-$200 transceiver
    5. transmit audio is not the best, but works (one reason i did not return my unit)
    6. the documentation is sparse, but you can find the original manual on the relevant groups.io
    7. you will not get any documentation with this unit; you will not receive a microphone, so you must use the built-in mic; you will get a power adapter
    8. there is no documentation on the purported ts-480 firmware CAT support – you may need a USB->TTL converter and a 4-pole plug, and will have to research that issue to see if supported
    9. forget about listening to AM BCB on this rig – ain’t gonna happen, although SWL AM reception was ‘OK’
    10. there is no charging indication; use the supplied charger; there is no voltage indication on the rig LCD

    here’s my experience after a quick check-out of the rig:

    – the firmware is R1.02v, while the latest is R1.02w – so not too out of date
    – muffled but copyable audio (transmitted via dummy load to a IC-705 qso recording; you can adjust/tailor voice via a menu item)
    – CW decoding works very well (another reason i decided to keep the rig
    – there is a ‘practice’ mode (menu #2.8) where you can see your keying decoded on screen – nice feature!

    – using solid carrier (CW), i found the following power out
    160 – 6W
    80 – 7W
    60 – 10W (surprising!)
    40 – 10W
    30 – 6W
    20 – 9W
    17 – 6W
    15 – 5W
    12 – 1.75W
    10 – 4W
    6 – did not test

    you’ll need some practice at freq entry, band changes, filtering and noise reduction, and importantly, volume manipulation – there are more than 30 menu items, some easily understood, others obscure; research the documentation and download a copy of the (tr)uSDX manual from DL2MAN

    band conditions are important, and i found that using one of my magnetic field loop antennas helped noise reduction; i was able to copy many signals with no problems, included ops running barefoot rigs

    i use the rig for copying POTA ops while having coffee on the patio… use a vintage miracle whip, i also managed to exchange info via ssb with an op across the state on the Atlantic from my patio on the Gulf of Mexico

    1. You were more than generous in your assessment of the Chinese junk… I got burned twice… I bought two different units,, with the same results.. I doubt this project will ever be truly usable and trustworthy. If you want a direct conversion transceiver, start with a pixi kit and add to it. They work better than the Chinese junk, and are very affordable, adaptable, and addictive… NL7QT

      1. HI
        I have a Chinese usdr. It costs 10 times less than my IC7300. But I can’t appreciate it being 10 times weaker. We performed QSOs from W to JA, even HS. With only 3W. For a small box it is excellent and if you do not have expectations from something that costs a little over 100USD, it is really miraculous. Original or copy. If you’re lucky, it works. If not … no
        YO4LHR’s Best 73

        ps: who buys an IC7300? :))

  19. Not all of us have CW… Do you intend to test/report the SSB capability of this radio? Mine is on its was from China as I type

    73 de G6EXF

    1. Hi, Jeff,

      So I’m primarily a CW op these days. I never got around to testing SSB other than making one SSB contact. I returned mine, so no longer have it (read more here). If you just ordered one of these, you likely have an updated version anyway. Let us know how well it works for you.


      1. Thanks Tom, I will do that. Yes, I’ve ordered the V2 unit. I’m hoping the rig will get here before we travel to Spain at the end of the month. Regularly operate as EA1/P… do a bit of POTA work but fancy some SOTA. Getting too old for lugging the G90 and battery etc up mountains.
        Will let you know.
        73 s.

  20. What are the settings to practice CW?

    How should the “key” jack be wired, using either straight key and dual paddle?

    Thank you!

    73 Mike N4ANO

  21. mine does produce terrible hum on rx on 160m
    also does not work on 6m

    – any hints?

    73 de dc2ru

  22. I bought mine last week on Facebook marketplace., locally. So far, it’s been kind of fun. Using a dipole, I’m hearing a lot, but haven’t tried sending CW yet.

    Mine came with no manual. I would like to know how to acquire a 12 volt plug to run it off a switching power supply. I can charge it with a Yaesu charger (from one of my HTs) and that seems to work.
    Also, is there a trick to wiring a mic? I have an old mic from a cassette recorder I might try.

    Scott, VA3SLJ

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