Important  Information provides help for constructors:  Preventing catastrophes and providing guides, fixes and modifications for your µBITx.  We are an information site only and not associated with HF Signals.

WARNING:  As shipped, your µBITx  v3  or v4 board will probably not be compliant with emission requirements.  It has been found to generate spurs and harmonics.  There are now simple fixes available to address these issues.  Make sure you apply them prior to operating the transceiver on an antenna.

CAUTION : If you power up the µBITX without the pull-up resistor the µBITX is likely to go into CW transmit. Make sure you install the 4.7k pull up resistor on the CW key pin!

v3 Board?  – There are known issues with WX brand TDA2822 chips (U1): Read this.  Earlier UCI and later socketed TDA2822 are not affected.   You will probably want to do the audio pop mod at least.

v4 Board? – If your audio is distorted see this article.  Note that audio output is reduced over the v3 board.  If you use a low impedance speaker you may need an additional amplifier module (LM386, TDA2822, etc.) to get adequate volume. The audio pop mod is not required on v4 boards.

v5 Board?  – It is too early to say as yet whether this is compliant, but early indications suggest that some boards on some bands may not be fully compliant, but they are a lot closer to compliance than v3 and v4 boards.  At 30dB down or more your spurs and harmonics will be in milliwatts!

SHIPPING:  µBitx orders were shipping within one or two working days of being ordered, but there seem to be delays with the v5 board currently of around 2 weeks. You should receive a shipping notification through PayPal once your product has been shipped. Estimated delivery times:

EU:         IndiaPost: 2-5 days  DHL: 2-5 days
US:         IndiaPost: 10 days     DHL: 2-5 days
Asia:      IndiaPost: 2-4 days   DHL: 2-4 days
AU/NZ: IndiaPost:10 days      DHL: 5-7 days

BITX QSO DAY:   Every Sunday – 3PM & 7PM Local Time – 7277 kHz in North America, 7177 kHz elsewhere.

LM386 mods (v5 uBITx)

The v5 uBITx has an LM386 for the audio amplifier stage. Philip G7JUR suggests connecting a 10 microFarad capacitor to the LM386. The +ve end should go to pin1 and the -ve end of the capacitor to pin 8. The easiest place to access is to solder to C75. This will give a bit more gain, and bass.

Ashhar Farhan VU2ESE commented that the LM386 distortion really increases with increased gain.  He also notes that more gain is not increased sensitivity.  He thinks a better idea might be to bypass pin 7 to ground with the 10 uf.  Either way, he suggests that Philip keep experimenting!

Jerry KE7ER suggests for uniform gain from 300 to 2300 Hz
with no capacitor gives at least 26dB  but under 46dB with a 10uF capacitor.
Adding a resistor in series with the 10uF cap would reduce the gain.


Nano Survivability

The Nano in the Raduino is readily damaged from wires touching 12v points, being exposed to RF, and from the Raduino being plugged in to the DuPont connector incorrectly.   Since the middle of 2018, these have been socketed, making it relatively easy to replace the unit.  Earlier units were soldered in place.

Ted K3RTA asks, “Have any of my fellow uBitx / Bitx40/20 owners experienced a different life span or robust survival rate between US$22 authentic Arduino processors over their cheap-as-dirt clones out of the Far East?”

A response from Jerry KE7ER

“Some of the Nano failures reported here can be attributed to not enough protection on the IO pins.  For example, a couple pins going out to a keyer may as well be protected from static discharge with series 1k resistors. Raduino should have protection against reverse power.  RF could conceivably get into some of these wires and zap an IO pin, though I tend to doubt that unless very long.

I had one of my stock Nano’s go south, though it could well have been something I said.  Several reports in the forum of stock Nano’s working out of the box, but sucking far more power than they should.  Suggests to me a Nano clone manufacturer with a quick go/no-go test, but not much more in the way of quality control.

When mine blew I then bought three from Elegoo at over $4 each, no troubles with them.  Expensive? Well not really, but there are Nano’s on Ebay for down around $2. Those $2 ebay boards have little pressure to maintain quality control, all they need to do is get their board a nickle cheaper and ship something that vaguely works. Seems likely that some would be built using somebody else’s reject parts.  Elegoo has a name to defend, they get good reviews, and likely monitor their sources closely for trouble.  At least, that’s my theory.  Seems worth a few bucks to (slightly?) reduce my odds of spending a day tearing at my hair.  What little hair (and time) I have is well worth $5.

I have yet to spend big bucks on a genuine Arduino Nano.

A response from Jack W8TEE

There’s no doubt that “real” Arduino boards rarely have any problems when used and are of better quality than the clones. I used nothing but the real thing for years. Somewhere along the line I started trying the clones…

I’ve been pretty lucky with the clones. The biggest problem I’ve had is the non-standard drivers. However, in most cases, downloading/installing the CH340 device driver fixes that problem. More recently, I thought I was seeing the driver problem again, but even installing the CH340 didn’t fix it. Turns out some of the clone manufacturers are using an ancient bootloader that is confused by the recent versions of the IDE. Fortunately, it’s easily solved. Use the menu sequence Tools –> Processor: “ATmega328p” –> ATmega328P (Old Bootloader) and do another compile/upload sequence and that should take care of it.

At times, I do feel guilty that I’m no longer using the “real” Arduino controllers. I try to make up for this by making a small donation every time I download a new release of the IDE. I think that probably more than makes up for the small profit they might have made had I purchased the real thing. I hope so. I also hope everyone else does make some kind of donation from time-to-time. Now, if they want to integrate a full symbolic debugger….


Summary of recommended spur mods

Jerry KE7ER,  provides summary details on the two know spurs mods:

Raj VU2ZAP recommended mod: 

Change out inductors at L5 and L7 with 1210 shielded surface mount inductors.

Here’s the post from Raj giving results for various inductor types at L5,L7:

And another post from Raj, affirming that he was using a yellow S+M brand 1210 inductor.

Here, Raj says that TDK-EPCOS parts work as well  (EPCOS was bought out by TDK):

Unfortunately, I don’t see any complete part numbers in any forum posts
from somebody who has verified with a spectrum analyzer that spurs were reduced.

I bought a similar assortment of TDK-EPCOS-Murata parts from ebay,
have not verified results with a spectrum analyzer.

The parts they actually ship may vary with the parts they can find.
But here’s what they shipped to me

480pcs inductor coil size 1210 1008 (24x20pcs) EPCOS TDK MURATA
B82422A3470J 47nH 1210 EPCOS  20pcs
B82422A3101K 100nH 1210 EPCOS  20pcs
NL322522TR120K 120nH 1210 TDK  20pcs
B82412A3181K 180nH 1210 EPCOS 20pcs
1008CS221XG 220nH 1008 COILCRAFT 20pcs
B82422A3331K 330nH 1210 EPCOS 20pcs
B82422A3471J 470nH 1210 EPCOS 20pcs
NL322522TR56J 560nH 1210 TDK  20pcs
B82422A3681K 680nH 1210 EPCOS 20pcs
NL322522TR82J 820nH 1210 TDK  20pcs
B82412A1102K 1uH  1210 EPCOS  20pcs
FSLM2520-1R5J 1.5uH 1008 TOKO  20pcs
B82412A1222K 2.2uH 1210 EPCOS 20pcs
NL322522T3R3J 3.3uH 1210 TDK  20pcs
B82422T1472K 4.7uH 1210 EPCOS 20pcs
B82412A1562K 5.6uH 1210 EPCOS 20pcs
NLV25T6R8J 6.8uH 1008 TDK 20pcs
B82422A1822K 8.2uH 1210 EPCOS 20pcs
NLV25T120J   12uH  1008 TDK   20pcs
NL322522T270J  27uH 1210 TDK  20pcs
NLV25T330J   33uH 1008 TDK    20pcs
NLV25T680J   68uH  1008 TDK   20pcs
B82422A1104K 100uH 1210 EPCOS 20pcs
NL322522T121J 120uH 1210 TDK    20pcs

Ashhar Farhan VU2ESE mod used in v5 µBITx:

The v5 µBITx provides  a different method of fixing spurs on the v5 uBitx,
primarily the low pass filter at L31, L32, C205 near the first mixer.

That filter removes the 90mhz second harmonic coming out of the 45mhz IF amp. Other possibly significant changes on v5 with regard to spurs would be the BFR93W’s at Q20,21,22  (to replace the MMBT3904’s) and the move to 220 ohms at R26 (was 470).


Ignition noise tips for your mobile uBITx

Robert N4FBZ has been experimenting with locating his µBITx in his vehicle, but says, “I’ve given up on trying to use my Bitx40 as mobile. Nothing I’ve done eradicates the ignition noise (and the alternator whine came back).”

Robert’s comments, and those of other constructors provide pointers to addressing ignition noise that may be helpful to others seeking to take their µBITx mobile.

Bob shares a couple of tips from this…

1) the radio is awesome, but very sensitive to impulse-type noise. The more barriers you can throw up between the noise source and the radio, the better! That means chokes in the power line, filter caps, and so on – and if possible, shielded wires! The noise may actually be getting in somehow via a path besides the antenna and knowing the spectrum could give a clue as to how it gets in.

2) if you’re trying to go mobile, grounding grounding grounding!!! While Bob’s best attempt  wasn’t good enough, it might be good enough in another situation. Ground everything you can… and don’t just trust to bolted-together sheet metal (frame). Also, usually drawing the power from a very low impedance source (direct to the battery) with good shielding and filters is the usual fix. In the case of Bob’s µBITx, it wasn’t enough.

Other suggestions:

  1. Ensure your µBITx is in a metal enclosure without large penetrations (like Nextion screens)
  2. Is everything inside the radio grounded to a common ground? (Power, antenna, board, raduino, mic and key jacks, etc.)
  3. How and where your antenna is mounted is important (i.e. far away from ignition sources, and with a good RF bond to the chassis)
  4. Use a common mode choke using ferrite material and with a number of turns of coax through it.
  5. Check for alternator whine.

A good resource:

  1. K0BG’s website contains information on bonding surfaces, dealing with ignition noise, spark plug wires, etc.


CEC Firmware Release v1.200 for all versions of uBITX

Ian KD8CEC has released his latest firmware.  This requires a minor configuration flag to be set to your µBITx version (3, 4 or 5) in the sketch before compiling and uploading the code to your µBITx.

Earlier µBITx versions do not require upgrading as no new features have been added to the firmware other than compatibility with the new v5 board.

A personal experience in building a uBITx

Ron K0EIA has just “finished” his uBitx build and made several contacts on CW and SSB with good reports. He also listened quite a lot to the contest, shortwave, and BCAM.

He says, “Receiver sensitivity is very good. My commercial radio is an old Kenwood TS-830, and I live in a quiet location up the side of a mountain. I have tuned very weak stations on the KW, and A/B tested with the uBitx. I have yet to find a signal that I can’t hear on the uBitx. It’s a good little radio.”

He finds it difficult to overstate his enjoyment of this build project.  He said “finished” above because there are still a lot of experiments to try with my now fully working radio.  Ron gives kudos to Farhan, HF Signals, Raj, and all the helpful people in the community.

  • v5 board
  • stock display
  • KD8CEC v1.22.

Ron first assembled the rig with stock software on an open aluminium chassis to make sure he understood the parts.  He also has a few pieces of test equipment which really helped: a frequency counter, an oscilloscope, and a software controlled dongle (Analog Discovery 2) that can do FFT (a poor man’s spectrum analyzer).


By far the most time was spent by Ron in reading through the IO Groups list postings and various blogs to understand details of the design or program features.  In turns out he had the encoder wired up backwards.  He also had several plug jacks wired wrong. etc. There were the normal assembler errors – each another research exploration.


Calibration was challenging for a few reasons. The calibration procedure for the stock software was fine, but it’s different from the procedure for the CEC software, so he had to relearn the procedure.

Ron had to figure out the CW Shift programming, to understand the design for sending a CW carrier.  He finally adopted Ian’s mathematical iteration approach using the uBitx manager 1.11 tool, with a spreadsheet and the frequency counter (the third calibration procedure learned).  Ron was able to get the uBitx to within just a few Hz of the frequency counter reading.   Ron says, “Of course my counter isn’t calibrated, and the uBitx probably isn’t temperature stable so this was mainly a learning exercise. I will be checking the calibration regularly though!”

Setting the BFO

The BFO setting was another significant challenge. Ron’s arrived from HF Signals with a setting of around 11052.  He could not hear anything because the BFO was putting the signal way outside the bandpass of the crystal filter.  He suspects that this is a common occurence, based on how many people report not hearing anything when they turn on their rig for the first time. Ron ended up with the BFO close to 11055.5 KHz, some 3.5Khz away.

Many on this list recommend using FLDIGI or other audio frequency displays to refine the bandpass. Copying this approach, he put his AD2 on the speaker terminals and looked at 0Hz-5000Hz.  Perfect!  Ron could see the bandpass of his crystal filter,  and adjusted this to get the bottom skirt down around 350Hz. This is still a work in progress since the same filter is suppressing the carrier on transmit, so there is a balance to be struck.

On transmit, Ron was able to put the AD2 on the RF output (using a 47dB attenuator tap on his dummy load! i.e. Don’t blow up your test equipment!.

Ron can look at the difference in the fundamental power on CW, vs keying the mic in SSB with no audio input. It looks like his carrier is suppressed about 30-35dB. This seems ok but he can still hear the carrier whine if he tunes near it using a nearby receiver.  He is still thinking about the tradeoff between carrier suppression and good low end audio.   He thinks he is likely to fiddle with the BFO some more sometime soon.

Loading software

Ron spent a lot of time figuring out which version was the latest version, for his particular board and his particular display, and getting all the steps squared away. Once it is figured out it’s just a moment to load, but it took quite a while to get everything organised.

Spurs and harmonics

The big question everyone has is what about spurs and harmonics. Using his AD2 as a spectrum analyser, Ron’s radio looks pretty clean, but he can see the third harmonic. Using his non-calibrated bench equipment, it looks like his build has the third harmonic down about 38dB.  He played around quite a bit with different bands, adjusting the gain on RV1 down to output of 5, 4, 3 watts. He also tried using CW and putting a 1000Hz at 50mV signal into the mic circuit. He says, “This testing is not conclusive because it’s at the upper limit of my skill and tools … but I definitely see the third harmonic and it’s not below 43dB on my amateur bench. So I’m going to do more testing …”

For the moment, Ron is not losing any sleep over a stray 500mV of RF signal. He is most likely simply going to add an external filter to take out the remainder of the harmonics.

Ron’s advice to a new person who is thinking about building this radio,  “it’s pretty obvious, but this is not a plug and play building experience. It’s not the linear kit build of the Heathkit days, with check boxes and step by step instructions. The uBitx is a kit of parts, you have to figure out how to put it together … and there are a lot of options and choices you have to make.”

Ron did not keep track of how much time he spent on my build, but it wasn’t soldering iron time. By far the time was spent reading through this group, other builders’ blog posts, and some basic electrical component theory (how does the click-switch thing on a variable pot actually work? How does a rotary encoder actually work?).

When he finally figured out how it is supposed to work, soldering up (or loading software) represented a small amount of time.  He has built a few things (smaller than this) with step by step linear instructions, but he took on the uBitx build as a step-up challenge.

Ron’s test equipment really made a difference.  He believes that some really skilled builders get it built using nothing but a soldering iron. However, in his view, that is an extra level of difficulty!    His advice is not to try to do this kit as your first beginner kit, and don’t handicap yourself with having no test equipment at all.

All this being said, he loved doing this build.  It was a great learning experience and he wanted to thank group members for being such a helpful and friendly community.


JackAl revised wiring harness instructions

Jack W8TEE has taken a number of steps back and reexamined the documentation for the JackAl wiring harness .   You can access the new instructions for assembling the harness by clicking on the reference link below.  Al has added a bunch of new photos to go with the written instructions.  Hopefully constructors will find the instructions to be much clearer.


Two tone generator for testing SSB

Mike K5ESS referred to posts by Raj VU2ZAP for an online generator that can provide two tones for testing your SSB output:

Another alternative is to download the application f-Generator for loading on to your cellphone.  The free version will give you a single tone, but you will need to pay a dollar or two in app to get two tones.

Mike also alerted us to an article in ARRL’s March/April QEX by Phil Salas AD5X describing a two tone generator fabricated from two Wien bridge oscillators that are available from Ebay. I’ve put together a PDF that describes the generator for those that might want to build one but don’t have access to QEX.


Collection of construction guides

Steve  N3SB has alerted constructors to a small collection of documents, photos, test results, and a calibration procedure that his Carroll County Amateur Radio Club (Maryland USA) has been putting together at:

The following link directly to the documents and reports: