Field Report: Testing the bhi Dual In-Line with the (tr)uSDX, making a big blunder, and P2P with Teri!

On March 30, 2022, I took my factory-assembled (tr)uSDX transceiver on a POTA activation at South Mountains State Park.

It was a “test flight” of sorts since I’d only had the (tr)uSDX for a few days and had not taken it to the field.

I wrote up an assessment from that initial POTA activation mainly to give other potential (tr)uSDX owners an idea of how well one of these super-affordable radios might perform.

Difficult to critique

It’s difficult to critique a 5 band HF radio that you can purchase as a kit for less than $100 and fully-assembled and tested for less than $150…shipped!

On the one hand, I think it’s one of the most amazing portable HF radio innovations of the past decade. It simply blows my mind that the developers (DL2MAN and PE1NNZ) could make this modest radio hardware do so very much. It’s truly a triumph of engineering and a fun little radio.

On the other hand, this isn’t a high-end radio, so we can’t expect performance like we’d see in an Elecraft, Icom, or Yaesu field radio, for example. I never expected this, in fact, but was very curious if the performance would be “good enough” for POTA or SOTA.  So many had asked me about buying a (tr)uSDX as their dedicated POTA radio.

I found using the (tr)uSDX for POTA was actually quite fun, and I certainly achieved my goal of activating a POTA park with it.

So yes, it’s good enough!

That said, I haven’t reached for the (tr)uSDX to do POTA or SOTA since last March because I prefer the performance characteristics of my other radios.

My biggest complaint, frankly, is that the audio fidelity is pretty poor. The noise floor of the (tr)uSDX is higher than most HF radios and audio amplification is very basic. I notice a lot of electronic noises (pulsing, etc.) in my unit. I find it a bit fatiguing to listen to for long sessions with my headphones. The internal speaker isn’t really a viable speaker for doing an activation–it’s more akin to an emergency speaker, if anything.

When plugged into an external amplified speaker, the audio is much improved. The pops and internal noises are still there, but it has better overall fidelity and the volume can be raised enough to hear weak signals (this can’t be easily done via the internal speaker).

It struck me that a DSP device might clean up the (tr)uSDX’s audio and noise floor a bit.

Enter the bhi Dual In-Line DSP filter

Sometime during the beginning of the pandemic, I reached out to bhi Noise Cancelling Products and asked if I could test one of their DSP units as a loaner. I’ve always felt that bhi manufactured the best DSP products in the amateur radio market.

At the time, I wanted one of my friends and contributors on the SWLing Post blog to test the bhi unit and see if it might help out a QRM situation that popped up at his QTH. I thought it would make for a great evaluation since I have little to no QRM at my home.

Graham, at bhi, kindly sent me a unit–the Dual In-Line Noise Eliminating Module–and as I prepared to forward it to my friend, his noise was no longer an issue. I can’t remember the details now, but there was no need to send it to him.

I notified Graham that I would like to test it myself, but that my plate was so full it would take time. What ended up happening, though, was I completely forgot about it due to a busy family life at the time.

I re-discovered the unit this year and spoke (apologized) to Graham at the 2023 Hamvention. Of course, he had no issue at all and was very forgiving. He’s a great fellow.

I thought pairing this bhi DSP unit to the (tr)uSDX would be a great way to, perhaps, cut down on the listening fatigue.

Fort Dobbs State Historic Site (K-6839)

On Wednesday, July 5, 2023, I had an opportunity to test the (tr)uSDX/bhi pairing at Fort Dobbs State Park.

I arrived on site, deployed my MM0OPX 40 meter End-Fed Half-Wave, and then set up the gear.

The bhi Dual In-Line is an external DSP audio amplifier, thus requires a couple of shielded audio patch cords and external speaker.

In the activation video, I show how I connect the audio out rom the (tr)uSDX to the DSP unit, then connect my Anker Soundcore Mini speaker to the bhi unit.


Note: All Amazon, CW Morse, Chelegance, eBay, and Radioddity links are affiliate links that support the at no cost to you.

On The Air

I started off this activation on the wrong foot.

After hooking up the (tr)uSDX to the bhi unit, then testing and adjusting the audio, I started calling CQ POTA on 20 meters.

Not only did no one respond, but the Reverse Beacon Network also did not pick me up.

What–? Very strange.

Keep in mind, I’m not terribly familiar with the (tr)uSDX and was monitoring the power meter which seemed to be moving with my keying.

After a while, I simply gave up, assuming something must be wrong with the (tr)uSDX, so I reached for the IC-705 which I also brought along.

As I started to disconnect everything from the (tr)uSDX, I realized that I had forgotten to connect the antenna–!!!


I reconnected the (tr)uSDX with the antenna and *boom* the HF bands had activity!

I left all of this in the activation video, of course, because I firmly believe that everyone–even reasonably seasoned POTA activators–can still make ridiculous mistakes!

In truth: had this been, say, my IC-705 I would have known via the audio that the antenna wasn’t connected. It would have been more conspicuous because there would have been no band noise. The (tr)uSDX, on the other hand, has a high noise floor so, to my ear, I was hearing the band.

That said, it was a pretty silly oversight not to hook up the antenna!

On The Air (For Real This Time)

Turns out, having an antenna hooked up makes a huge difference!

In nine minutes, I logged the ten stations needed to validate the activation. I continued calling CQ POTA for another seven minutes and worked seven more stations.

Seventeen stations in sixteen minutes made me quite happy!

No doubt, the (tr)uSDX can easily take you through a POTA activation–it’s just a bit noisy.

P2P: Trying to work Teri (KO4WFP/VE1)

While I was on the air, I got a Ham Alert that my friend Teri (KO4WFP) was on the air, activating a park in Nova Scotia.

Teri has posted a brilliant series of field reports from her summer trip to Nova Scotia. I had tried hunting her from the QTH, but on those days, propagation simply wasn’t there.

Teri was on 17 meters, a band that the (tr)uSDX doesn’t cover, so I grabbed the IC-705. Of course, the 40 meter EFHW isn’t resonant on 17 meters, so I also needed to add my Elecraft T1 antenna tuner as well.

I could hear Teri on the 17 meter band, but barely. I called for her quite a few times, but she couldn’t hear me. Little did I know at the time, but she was doing this activation from her car in the rain! You can read her field report by clicking here.

After trying to hunt her for a few minutes, I ran out of time and  started to pack up the IC-705. Then one more Ham Alert came through indicating she’d moved to the 20 meter band.

I re-connected the antenna and hopped on 20 meters where she was *much *louder and more stable than she was on 17 meters. It only took one call to work her Park-to-Park. Woo hoo!


Here’s what this activation looked like when plotted out on a QSO Map.

Note that my contact with Teri does not show below because the QSO Map couldn’t map her point in Nova Scotia with a /VE1 call.

Activation Video

Here’s my real-time, real-life video of the entire activation.  As with all of my videos, I don’t edit out any parts of the on-air activation time. In addition, I have monetization turned off on YouTube, although that doesn’t stop them from inserting ads before and after my videos.

Note that Patreon supporters can watch and even download this video 100% ad-free through Vimeo on my Patreon page:

Click here to view on YouTube.

Did the bhi Dual In-Line DSP Help?

Yes it did.

As you’ll hear in the video, the DSP–which I actually kept at a pretty low level–definitely helped the overall noise profile of the audio. I will use this unit next time I take the (tr)uSDX to the field.

Of course, you could still hear some of the pulsing noises that the (tr)uSDX produces, but the overall noise floor was much lower.

As I mentioned earlier, I feel like bhi DSP units are the best in the world of amateur radio. They’re specifically tailored for this application.

Thank you

Thank you for joining me on this fun little activation!

I hope you enjoyed the field report and my activation video as much as I enjoyed creating them.

I hope I don’t try to operate without an antenna again. 🙂 If I do, I’ll certainly include it in the report and video. It’s important to know that we all make mistakes from time-to-time.

Of course, I’d also like to send a special thanks to those of you who have been supporting the site and channel through Patreon and the Coffee Fund. While certainly not a requirement as my content will always be free, I really appreciate the support.

As I mentioned each time, the Patreon platform connected to Vimeo make it possible for me to share videos that are not only 100% ad-free, but also downloadable for offline viewing. The Vimeo account also serves as a third backup for my video files.

Thanks for spending part of your day with me! Have a brilliant week!

Cheers & 72,

Thomas (K4SWL)

10 thoughts on “Field Report: Testing the bhi Dual In-Line with the (tr)uSDX, making a big blunder, and P2P with Teri!”

  1. Tom-

    I’m glad you found the problem and overcame it! I think we all have challenging Activations at times- things we can laugh about after the fact. 73- K1SWL

  2. Well you are mortal! I had a good laugh… thanks for that.

    I too own the same BHI filter… but I’ve never used it. You’ve renewed my interest in it’s anxillary utility. Can you demonstrate the DSP unit again, perhaps with another radio?

    de W7UDT

  3. Thomas –

    Hi Hi! So funny to hear myself on another’s person rig. Thankfully I didn’t flub much except for your name. I really appreciate you hunting me that day! It was wonderful hearing so many friends on that activation.

    I learn something from all of your posts. The BHI filter – wow! When I was at Truro Post Office Historic site, power lines ran right by that site and I had so much noise, I decided I would no longer attempt any urban parks. However, watching the video for this activation made me wonder if that would counteract such noise and allow me to work urban settings QRP? Any thoughts?

    This is such a great hobby – always something new to learn.

    72, Teri KO4WFP

  4. I’ve been considering a (tr)uSDX as a backup portable radio and this review is very helpful.
    Recently, while attempting a POTA activation I had a similar experience as you. I setup everything and spotted myself on POTA, and called CQ 20m SSB. I called CQ for a considerable time.
    I couldn’t hear any transmissions, nor did my CQ get any responses, so I put it down to bad propagation, really bad propagation! I called CQ some more, and even saw that my calls had been picked up and spotted on POTA, which seemed strange. Decided to check all my connections which I should have done before I started. Indeed, the coax and the TufteIn 9:1 EFRW antenna weren’t connected!
    Eventually I ran out of time to get my 10 contacts after everything was connected properly but I did learn a valuable lesson about checking my setup before going on the air.

  5. I have a different version of the uSDX transceiver, knob, display on the end, connectors on the rear. I have played with it and it can work. For the money one can test their liking of QRP without spending a lot. I did find the receiver to be somewhat bad sensitivity, 1uV needed for any signal detection. Also the power output dropped off on the upper bands, good 5W on 80& 40m, but like 4W on 20m, on 10m 2.5W. Does take some learning to get use to the rig menus and how to set things, one would expect this with only 2 buttons, a knob and a display. And yes one cannot expect much from the small speaker. I loaned my uSDX to a friend who was just getting into HF and it convinced him he want to get into HF. He actually checked into our state phone net with the rig. After playing with the uSDX I wondered how Gillians Islands would have wanted one, hi. 73, ron, n9ee

  6. The audio problems with the (tr)uSDX have been largely solved. There’s a not-easy hacky alteration you can do to fix it on a first-gen board, but future boards will have that fix included.

    I like the radio enough I’m about to give it a shot, but yeah, it is not an easy radio. It’s more like an advanced homebrew radio. There’s a great community to help, but it does take work and skills to get it working well.

  7. After a few days consideration and several re-reads of this post I have decided to order a (tr)uSDX to try out in the field; it’s hard to argue against adding another lightweight HF rig to the collection at that price!

  8. Hello Thomas, in my opinion the (tr)uSDX is a very entertaining toy, I don’t know CW but in phone it gives me very good results. There is a link to a short video …
    I have completed the equipment with K6ARK digital interface and DL2MAN 18650 battery holder, they make a very good combination.

    César CA7OKD

  9. I’ve been testing the (Tr)uSDX over the summer with digital modes – first at Field Day, where I believe my antenna pairing and/or choice of modes was not terribly indicative. During the month of August, I’ve paired this radio with a homebrew dipole and the FT8CN Android app, and have had considerable success in activating parks at will on 40m.

    I’m running the (Tr)uSDX, AT-10 antenna tuner, and a Digirig soundcard interface. Powering this is a cell phone battery bank (Romoss 30,000mAh Power Bank Sense 8+), and a USB-C to 3.5×1.35mm cable, which is what the radio accepts. The USB-C port on the battery pack is a PD (Power Delivery) port, which will provide 18v max output – enough to obtain full power out of the (Tr)uSDX. I’ve also put together an 8-cell AA battery pack using Eneloop Pro (black-label) rechargable batteries. The radio can also be run from 18650 batteries, but those cells are 3.7v each, and a 4-cell pack kisses the upper specification of acceptable voltage for the radio. In testing, using 4 ea 18650 batteries actually made the (Tr)uSDX a 10w radio – but I wouldn’t recommend this.

    YouTube short here:

Leave a Reply

Your email address will not be published. Required fields are marked *

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