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.

Vic WA4THR observed on his first BitX40 trip that he didn’t have ignition noise, but the alternator whine was horrible.  He found it was coming through the power line, and not the antenna.   The noise didn’t change when the antenna was disconnected.

He used a Radio Shack “Heavy Duty Automotive Electrical Noise Filter” (cat. no. 270-051B) in series with the power lead and was amazed that it actually quieted everything.  This was subsequently installed inside the BitX40 plastic case.

On the road, the receiver now sounds as good as when at home on a power supply. Vic suspects that these filters were designed for CB radios, and are the right size (rated 10 amp) for QRP.   You can often find them quite cheap, too.

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:


Caution for JackAl Board owners

Jack, W8TEE and Al, AC8GY produce the JackAl Board add on for the µBITx.  They are warning that two JackAl owners have reported that a voltage spike destroyed their RA8875 display.

Al has looked into this and found that there is a very narrow voltage window on the display. Buydisplay confirms that 4V on the 3.3V line can ruin the display. From what we can determine, voltage spikes were the culprit in both cases.

What the JackAl team is doing is creating a very small PCB that will clamp the supply voltage to the display. Parts for the board will cost less than $2.

They will send one of these PCB boards to JackAl owners at no charge with a request and a SASE.

Further details will be provided when the boards come in.  Jack and Al are also expanding the documentation and hope to have a new assembly manual shortly.  Announcements will be made on the BITX20 IO Groups list and this article will be updated accordingly.


Add-on board for uBITx

Nick VK4PP is working on a nice little add-on board for the µBitx with the following mods incorporated:

  • 200hz CW Filter
  • Mic Preamp (SMM2167 Module)
  • LPF section (Dual relay per filter)
  • POP fix for earlier v3 boards, and
  • High Pass Filter on RX for BCI option.

Nick is designing it for use with through hole components with the exception of the 100uh inductors underneath the board, which will need to be 1206 Surface Mount devices.  At this stage he is hoping to provide the board at $5 each plus post (VK-$1, DX-$3).


Mini-microphone for your uBITx

David N8DAH suggests you can use your µBITx stock switch and microphone element with this nifty mini-microphone case from Kit Projects.  They cost US$10 plus shipping.  These are 3d printed  with all hardware included (Mic’s use the stock element and tac button that came with your bitx40 or ubitx).

Kit Projects has red and black microphones right now and grey is coming soon!

The also have 3D printed mini paddles available to purchase, that may be of interest to µBITx constructors.