A couple weeks ago, I posted my initial thoughts about the Chinese uSDX/uSDR QRP transceiver.
In short, it wasn’t exactly a glowing review.
I’ve now tested the uSDX at home for a couple weeks and decided to send it back to the eBay distributor.
I made a short video detailing the reasons why I’m sending it back (see blow), but in short there are two main reasons:
1.) The receiver and audio
With that in mind, I have to assume mine is one with an incredibly inadequate receiver.
My uSDX receiver overloaded when in the presence of pretty much any strong-ish signal.
As an example, one of the first signals I tuned to on the CW portion of the 20M band–K4NYM activating a park in Florida–had FT8 audio bleeding in from over 20 or 30 kHz away. K4NYM had an S9 signal, but he was very much a portable operator, not a blowtorch contest station. The uSDX should have easily been able to handle this situation.
On my unit, if you tuned to a strong CW signal (or worse yet, a pileup) it opened the receiver window so wide that signals across the band bled through. There was essentially no selectivity.
I quickly learned that I couldn’t trust this uSDX unit during a park or especially a summit activation. If I had the good fortune of attracting a small pileup in the field, I knew the receiver would fall apart and it would be a real struggle to work anyone. I tried altering some of the uSDX settings, but nothing helped.
On top of that, the audio amplification chain produced a lot of unwanted hash and splatter.
Even when the audio was turned to “0” you could still hear splatter from receiver overload punching through the speaker. It was ever-present.
To be clear, I’m not terribly picky about audio in field transceivers. I don’t expect contest-grade performance in this class of radio. But the audio needs to have enough positive characteristics that it’s functional. I believe my uSDX unit pushed those boundaries too far.
It’s no exaggeration to say that it had the least refined audio of any QRP transceiver I’ve ever tested. It was fatiguing to listen to this uSDX unit for any meaningful length of time.
The transmitted signal
As I reported earlier, I took the uSDX to my buddy Vlado (N3CZ) who hooked it up to his service monitor. We discovered (with little surprise) that the transmitted signal wasn’t exactly clean. I’d read in advance that some Chinese uSDX units produce a signal that likely falls below FCC signal purity standards and I now suspect this unit is either very close to or exceeds that threshold.
We didn’t want to count on the measurements from this older service monitor because it had been some time since its last calibration and there was a slight issue with the BNC input. Still, we repeated the test numerous times across the bands and the average showed consistency in results. The uSDX produced spurs on harmonics and noise in the signal.
The noise was especially noticeable when compared to that of my Elecraft KX2 which we also tested.
I’ve been contacted by other Chinese version uSDX owners who found their unit had a fairly clean transmitted signal. I’ve also read numerous reports from owners who tested their unit to find that it didn’t meet FCC specs.
I assume quality must vary greatly from unit to unit.
I like knowing I’m a good neighbor on the HF bands, so I simply couldn’t live with the signal this uSDX produced and I had no desire to attempt to modify it because of the receiver issues mentioned above. It just wasn’t worth my time.
I made this quick unscripted video only moments before shipping the uSDX back:
Reminder: This is not the uSDX Open Source Project
I’ve been careful to note that my unit is a Chinese version of the uSDX transceiver.
In case you are unfamiliar, the uSDX is an SDR transceiver that was originally developed on the hardware of the original QCX by Guido (PE1NNZ). Manuel (DL2MAN) also worked on this project and encouraged more interest and the uSDX spun off into its own separate project, with its own discussion group.
As Hans (G0UPL) notes:
[These Chinese uSDX transceivers] aren’t “clones” because uSDX is open source and any productions of the radio by anyone are legitimate. Having said that, you may question what quality and support you will get.
[…]The uSDX, and particularly its eBay implementations, are not a high performance transceiver.
[…]The eBay implementations also often suffer inferior components and poor design choices which are not compatible with the original uSDX design.
As Hans implies, the homebrew/open-source version of the uSDX–for those who have built them–performs much better than the Chinese versions.
Still, at time of publishing this post, I know of no complete uSDX kit that can be purchased [please correct me if I’m wrong about this] so builders would need to source all of the components on their own. This could get pricey for those of use who don’t have a large inventory of parts.
The Chinese uSDX transceivers are appealing because they’re so darn accessible.
My advice? Skip the Chinese uSDX
I’m sure there are better examples of the Chinese uSDX out there on the market–ones that might be worth keeping. But I have to admit: at time of posting (December 20, 2021), I suspect “good” Chinese uSDX models are the exception, not the rule.
My advice would be that if you decide to purchase a Chinese version of the uSDX:
- Please test its transmitted signal before hopping on the air.
- Purchase it from a retailer with the highest customer feedback points in case you experience an issue.
- If you have the skill and desire, plan on modifying it to tweak performance.
If you own the Chinese uSDX, please comment with your own thoughts and experience. Again, I’m not claiming all versions will have the dismal performance of the unit I purchased, but I think there is a reasonable probability.