Because I bought one so you do or don't have to.
This radio is a budget version of the tr)uSDX by DL2MAN and PE1NNZ. All clones are basically the same but they're all a mixed bag of reviews. Some say they perform very well and are similar to the original, but others say they're destined for the trash bin. However the one I bought didn't really have a review worth the effort, so $100 later, here's my honest review.
Let's talk about the pros and cons of this radio, just from watching videos and reading other reviews.
Pros
This radio is VERY small - you could honestly take it anywhere. Vacation, the park - wherever you want to go! It also uses the same firmware that the uSDX uses, so it's probably interchangeable if you have custom firmware. This also features separate volume and tune knobs, both of which are rotary encoders. It is also multimode. SSB and CW are both standard features on this radio, and there is also a built-in audio filter that goes as low as 50Hz wide! Time will tell as I use this as to how functional it is, but so far I seem impressed just from the ads! And components? Most if not all are 100% replaceable should something fail. Especially the final Class E stage, where they used 3 or 4 BS170s in series with one another to push at most 5 watts out of this thing. Now THAT'S impressive. Or the fact that the 1602 LCD is replaceable by just pulling it up and out of the socket.
Cons
Now for the cons, and the most glaring one is the speaker. What a pathetic attempt at huge sound. It's so tinny it belongs on a child's toy. Of course there's an external speaker option but there's really no benefit in lugging around a speaker. I can't imagine what it'd sound like with headphones but I feel that the audio stage is starting to remind me of a Pixie kit...
This also is not an all-bander. You only have access to 40, 20, and 15 meters. While this is okay with a travel radio and are the most popular bands, it's not good for the long run or as a main rig. And it's QRP, so it's really only useful for CW contacts. You'd be extremely lucky to make an SSB contact with only 5 watts of power, and while it can be done, it's very unlikely. I had a hard time with 10 watts as it was when I first started out on HF, so save yourself some disappointment and only use this radio for CW. Or, if you can figure something out, use it for FT8 or another low power digital mode.
Overall?
It is as budget as radio can get. The receiver is somewhat poor and I almost bricked it at least once. In hindsight I should've stuck with a QCX or QMX but this is what I got and this is what I get to work with. No problem though, as I may have a few solutions.
First, we need to tackle the audio popping sound. Every time a button is pressed the receive audio introduces an awful and loud popping noise, even on the lowest volumes. To remedy this, we can install a filter along the audio lines to take the pops and clicks from God-awful to actually somewhat useable.
These pops are no more than the MCU executing code. Most SDRs mute the audio lines or even filter them internally when a switch or button is pressed. Since this is a budget and a low-cost clone, they skimped out on this - surprise, surprise.
Next comes eliminating unnecessary code. This is a bit advanced as these radios are wired a certain way. It's going to take me forever to reverse engineer this code but I'd like to remove the attenuators and the extra bands. I just need a simple Pixie-esque transceiver that at least has code in it for iambic keying. Hopefully I can also manipulate the audio issues via the software as well.
If I had to absolutely review this radio, I'd give it a 3/5. I've actually considered sending this radio back and in the next few days I might do so. I know it was only $100 but that was $100 I could've spent on a QCX at least. Not a huge loss but more of a lesson. There are better QRP rigs out there.
Stick with me as I break open this radio and get it up to useable again!
Fix 1: Receive Audio
This one is the most glaring problem. Every time I push a button or change into a specific portion of the band, the radio likes to pop. One explanation for this is that the microcontroller does not mute the audio amp while it's executing an instruction. There are many ways to fix this (or at least reduce the pop), but I think I'll settle for what is called a diode clamp.
To do this, we need to take 2 low-voltage diodes, namely Schottky diodes. The 5711s I used for the scanner converter should work well since these have a turn on voltage of around 0.2-0.3V. What this does is takes the voltage spike (the popping) and "clamps" it to the point where it is nowhere near audible. It won't 100% fix it but it should attenuate the popping down to a point where it's more of a click than a pop. I discovered this hack on the Pixie, which most QRPers claim pops switching between transmit and receive.
If that doesn't work (I highly doubt it won't), you can also try filtering the audio using the built-in filters. Appropriate values I've found on this radio are 100Hz for CW and 1800-2400Hz for SSB. It still pops but it isn't as horrible as it would be if the filters were wide open.
The amplifier also likes to howl at high volumes. This is the result of it oscillating which means that I need to either turn down the volume or reduce the gain capacitor. I think you know which one is easier.
Fix 2: Necessary Bands Only
When I broke open the radio, I discovered that this model has areas for more low pass filters. Since I only plan to use this radio on 40, 20, and 15 meters, I need to modify the firmware to only allow me to switch to those three bands, as the other ones are pretty much useless. The others are severely attenuated either because the already-installed filters are bandpass filters or the filters for these bands are missing.
Fix 3: Bloatware
I feel that this would also free up some space which I believe limits the headroom of this radio. By removing some unnecessary functions (ie, auto CQ-ing, attenuators, etc.), I could free up some space for the actual essential functions like audio processing. When compiling, I noticed that there were only 500 or 600ish bytes of free space left, meaning that this firmware takes up 99% of the chip's storage space! No wonder these radios are crap!
Fix 4: Sidetone Pitch Correction
Not that big of an issue, but it's rather annoying when the sidetone of this radio is nowhere near 600 or 700Hz. Sure, the offset might be correct, but the tone is absolutely awful. Firmware issue? Most likely. Fixable now? Probably not. The firmware is about 10000 lines long so...that's gonna take a while...
I've found that the firmware uses a Minsky algorithm. This is basically a fancy way to produce a close to perfect sine wave, "close to perfect" being the main issue I'd imagine. A few tweaks to a line of code that produces this tone would most likely clean it up to the correct frequency.
Fix 5: Buggy CW keyup
This is a known problem with this radio. I'm fairly certain that the jack is wired up wrong. I have a TS mono plug and whenever I plug it in fully, the radio keys up! If I leave it 1/4 to 1/3 of the way out, I can key it normally. This tells me that the keying must be between the ring and the sleeve, not the tip and the sleeve like it normally should be.
So what does this mean for an iambic or paddle keyers? We'll have to change some configuration most likely. Maybe not, but I find it very unusual that the ring is the positive signal on a straight key using this radio. No biggie, but just keep that in mind if you use a straight key with this radio. You'll most likely have to rewire your TS tip to a TRS tip, and wire ring (+) and sleeve (-) as the signal pins.
Funny enough, the more I use this radio on receive the better it starts to sound. Yeah, it's not as great sounding as my FT-891 but when a zero-beated CW signal comes in, boy does it come in strong! I have yet to test the transmitter but that is my next goal.
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