Many thanks to QRPer.com reader, Charles, who recently sent me the following question:
Thomas, I’ve watched a number of your videos and read your activation reports. I’m studying for both my Technician and General class license right now and hope to pass both in one session later this month. I’m also learning CW.
I consider myself an audiophile and appreciate good audio fidelity. I know that amateur radio modes are narrow and by their very nature have less audio fidelity than commercial broadcast modes.
I’ve already obtained a Kenwood TS-590G for the shack. It was practically given to me by a friend. I’m very pleased with its audio fidelity especially when I connect it to an external speaker.
Next year, I plan to buy a dedicated QRP field radio. Out of the radios you’ve owned, what are your favorites in terms of audio fidelity. Also, what are your least favorites?
What a great question, Charles!
Being an audiophile, I’m sure you understand that this is a very subjective area: one person’s idea of good audio might not match that of someone else’s.
I can only speak to how I evaluate a transceiver’s audio.
What makes for good audio?
A lot goes into what I would call “good audio” in an amateur radio transceiver.
To me, “good audio” means the radio
produces clear accurate sound,
has stable AGC (Auto Gain Control),
has audio properties that benefit amateur radio modes like CW and SSB,
has enough audio amplification to be heard in noisy field conditions,
and has little to no internally-generated noises leaking into the audio amplification chain. (In other words, a low noise floor.)
In contrast, radios with poor audio
have a high noise floor or produce audio hash making it difficult to hear weak signals,
have speakers that become distorted at higher volume levels,
have poor AGC characteristics which lead to pumping,
and are simply fatiguing to listen to during extended on-air sessions (like long activations or contests).
I would add that a good receiver front end is an important part of audio because it keeps imaging and overloading at bay, thus producing a less cluttered and noisy audio experience.
My field audio favorites
I’ll keep this discussion limited to QRP field portable radios. There are numerous 100 watt desktop radios with excellent audio because those models aren’t trying to limit their current consumption like field radios typically do. They can use more amperage to benefit audio amplification and push a much larger speaker.
In addition, I’ll limit the scope to field radios with built-in speakers. There are some great CW-only radios out there that lack an internal speaker but have great audio (thinking of the Penntek TR-35 and the Elecraft KX1, for example); choice of earphones or headphones can have a dramatic effect on audio. That’s a different discussion altogether!
Best audio: My top three picks
The following are three of my favorite portable field radios in terms of audio quality. I limited myself to three simply because all of the radios I use regularly in the field have what I would consider good and acceptable audio.
The following are simply stand-outs, in my opinion:
The (tr)uSDX has been a much-anticipated QRP transceiver for those of us who love playing radio in the field.
What’s not to love? It sports:
Up to 5 watts output power
CW, SSB, FM, and AM modes
A built-in microphone
Five bands: 80, 60, 40, 30, and 20 meters
A super compact and lightweight form factor
An open-source hardware and software design
Super low current consumption in receive
A super low price of roughly $89 US in kit form and $143 US factory assembled (via AliExpress, but there are numerous other group buys and retailers)
Frankly speaking, this sort of feature set in such an affordable package is truly a game-changer. Back when I was first licensed in 1997, I could have never imagined a day when a general coverage QRP transceiver could be purchased for under $150 US. The price is almost unbelievable.
My initial impressions
On Wednesday, March 30, 2022, I took the (tr)uSDX to the field to attempt a Parks On The Air (POTA) activation. I had only taken delivery of the (tr)uSDX about 15 hours beforehand and had only had it powered up for a total of 30 minutes the previous day. Most of that time, in fact, was checking the power output at various voltage settings into a dummy load. I did make one totally random SSB POTA contact shortly after hooking the radio up to my QTH antenna.
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.
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.
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.
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.
I had my calendar marked for February 15 to check the site again for the 3rd batch as I thought that was the day they planned to issue another pre-order.
My buddy Eric (WD8RIF), who is the President of the Athens County Amateur Radio Club (ACARA), contacted me yesterday asking if I knew of any QRP kits designed with phone/SSB operation in mind. One of ACARA’s members was searching for one.
The only other kit I could think of was the new (tr)uSDX. When Eric asked for a link to the product, I went to the Rowaves site and discovered that they were taking pre-orders for the third wave of kits. Like, right then and there!
Without hesitation, I added one to my shopping cart and checked out.
I thought perhaps Rowaves caught up and no longer had a waiting list. This morning, when I checked the site again however, it appears they’ve sold out of the third batch.
Without Eric’s prompting, I would have never thought to check the Rowaves site yesterday.
Side note:There are various (tr)uSDX group buys out there. I don’t completely understand how they work, but perhaps someone with more experience can comment. DL2MAN has information and links on his webpage.
If I’m being brutally honest, the (tr)uSDX kit is a bit intimidating for me. I recently referred to myself as a “gross motor skills” kit builder. I think that’s a pretty accurate description. I’m fine with through holes, simple toroids, and very clear, illustrated instructions. Truth is, I absolutely love building kits. But I’m not an electronics engineer, so when instructions are vague, I can get lost quite easily.
The (tr)uSDX toroids don’t look terribly complicated and all of the surface mount components are pre-installed. Still: it’s a wee kit and I’ve yet to check out the build instructions.