Glitch on CW keying on uBITx

Bob N1KW has identified the cause of the brief glitch on going into TX on CW with the µBITx.   While analysing the circuit Bob realised that the large capacitor C52, which is charged during receive, would feed back through R52 and R18 keeping the receive path (Q10, 11, and 12) after the balanced modulator “hot” for a brief period. When the transmit path is activated, the receive side of the circuit is going to remain on for some period of time due to the time constants of C52 and its loads. It is understandable that if both directions of the circuit are on, it could oscillate during that time!

To resolve the issue he simply added a diode in series with R52 (cathode toward C52) so that C52 can no longer back feed power to Q10, 11, and 12 upon initiation of transmit state. Now the transmitter output looks perfectly clean on the spectrum analyzer at beginning of TX. Shorting the diode causes the problem to show as before.

The same issue could apply to C64 when transitioning from TX to RX but at least there will not be spurious emissions going out over the air.  He plans to add a diode in series with R66 in the same manner just for fun.

Note that in KD8CEC firmware you can add a keying delay to fix this issue in firmware.


Nextion display and a second arduino

Ian KD8CEC has now given us part 2 of his description of the latest firmware update (v1.097).   If you have a Nextion display, and add a second arduino you can have a higher quality s-meter and multi-band signal monitor on your µBITx.

For more details go to Ian’s website at

The wire up diagram follows:

The second arduino echos information in one direction from the main raduino via the i2c serial channel which is faster than via serial port.  It uses a dedicated serial port to output the signal again, potentially making the sampling faster for taking signal strength readings.  It will be interesting to see what effect this has in practice.

KD8CEC v1.097 Beta will be released shortly

Ian KD8CEC has been busy again in conjuring up new features in his CEC firmware.   He is tempting us with descriptions of two new features:

  • Nextion display update that makes it easy to adjust keying speed and to select the keyer type (Iambic A, Iambic B or Straight Key) even while in TX
  • Adding an additional arduino, connected to the Raduino via i2c, to provide an S-meter function.

The first feature is well explained by the photo above. The second feature is a bit more difficult to describe.   By adding a US$3 additional arduino the µBITx now has double the number of analogue and digital ports and another 32K of program space.   This could be a fun ride!  The first function is a basic one, but an important one.   A much more sensitive S-meter.   But wait there’s more, as yet to be fully described.  If you already have a Nextion screen, it looks like you may be in line for a half decent signal analyser function.

Connecting up the arduino

The circuit is pretty straight forward, and involves just a couple of resistors and a capacitor, along with wiring to +5v and ground, and the two i2c lines.

VK3 uBITx get together

Glenn VK3PE reports on a VK3 event at Chelsea Beach with  a few pics of the ‘event’.  Chelsea Beach is  about a 20min drive Sth of Melbourne central.   The group met at a beachside table under shade cover to share their experiences in building µBITx.    This looks like a good ideato replicate elsewhere.

The photo below shows Peter VK3YE and uBITX on 40M using an EFHW antenna:

And of course Peter’s µBITx needs to get a shot as well:



Tips for building into VU3SUA enclosure

Dave, N8SBE completed a build of the µBITx last night in one of Sunil’s µBITx enclosures, and he has helpful observations for others using this case.

Front panel PCB

In spite of the pictures, the main board must fit OVER the front panel PCB, so that you can mount the LCD display up close to the front panel.

Dave put vertical male pins on the ends of the front panel PCB, which meant that there was insufficient clearance.   If you want to put male pins on the front panel PCB, you should use the right-angle ones (and then the mic connector will be a tight fit against the chassis mount four-pin mic connector, but I was able to just make it work).

He ordered a Dupont kit of male pins, female sockets and housings from Amazon and a suitable crimp tool:


The crimp tool works fine, but Dave spoiled a few female sockets before I got the hang of it.

If you are crimping female sockets on the ends of the original wires that come from the Relimate sockets on the µBITx (trim them to 8 inches first, then you can use the extra for other wiring, see below), then it seems the wire gauge is about 22 gauge, but the crimp die in the centre of the tool that is marked for 22 gauge is too large and won’t crimp the wire properly. He ended up using the crimp position for the smallest wire size, and it worked fine.

It is also important to insert the female socket in the tool first (Dave found that by clicking the tool 3 clicks it closed the jaws just enough to make it easy for me guide the socket into the tool), then push the female socket in far enough so that the box that encloses the male pin is completely outside the dies on the back side of the tool.

Then lightly pressing the handles to keep everything in place, insert the stripped wire into the back of the female socket, and crimp.

The wire should be stripped only about an 1/8″ of an inch, and the insulation should be inserted into the back of the female socket such that the bare wire bundle is crimped with the smaller crimps, and the insulation is held by the larger diameter crimp at the back end of the female socket.  If you strip off to much insulation, you will either fail to get the insulation into the back crimp, or you will force wire into the female socket area, and that will interfere with the male pin when it is inserted.  If you’ve done everything correctly, tugging on the wire shouldn’t make it come out, it will seat correctly on a male pin, and you should not have to resort to soldering anything.

Soldering crimp joints is a BAD idea, not only because the clearance in the female connector bodies is very close, but the solder that wicks into the wire bundle will stiffen the wires past the crimp, and create a stress point that will eventually break the wire if subjected to vibration and movement.

Dave ended up using Dupont housings/connectors on the Audio, Digital (both 8 pin), Mic (three pin), Volume (three pin), encoder (4 pin) and speaker connectors (2 pin). 

When you cut the ubitx supplied analog and digital wire bundles to the recommended 8 inches, you end up with enough left over that you can make all the other front panel connections with using the left over wire.  You can even select the appropriate colours, as documented in the wiring instructions on the HFSignals website.

Small PCB for Encoder

Dave completely missed that there was a small PCB board included for the encoder switch.  He ended up tack-soldering the ends of the four-wire bundle coming from the front panel PCB to the actual switch pins.  It works fine.

Wiring the volume control

Dave somehow got the wiring backward on the volume control (hi end vs. low end), and was “surprised” by a VERY loud noise when he first powered it up.  If you mount the control with the soldering tabs on top so you are viewing them directly when looking down at the rig with the top off, then the correct colours from left-to-right (with the front panel closest to you) are yellow, orange, green (given the wiring colors shown in the wiring section on the HFSignals website).

Power supply wiring

The power supply wiring was an issue, due to the power on/off push-push switch.

It is NOT meant for soldering, as the tabs are practically impossible to solder to (don’t know the material, but it does NOT accept solder), and the body melts in an instant. The tabs are meant to be used with push-on tab crimp connectors (You can find suitable ones at the local auto store in the electrical section).

Dave still wanted to use the PCB board, so he ended up inserting the power switch tabs through the board, pushing the auto tab crimp connectors on, and then tack-soldering the crimp connectors to the board.Ugly, but effective.
Before Dave figured that out, though, he had partially melted and loosened one of the power switch tabs.   
The rest of the power PCB board wiring went OK.  Dave put a three pin header and connector on the end of the board going to the ubitx supply wiring.  Originally he used a right angle male header, but discovered that this interfered with the mounting bracket (and likely the board when installed) for the digital interface PCB.  The solution was to bend up the pins from the board at a 45 degree angle.  Ugly, but effective.
Check the actual wiring of the DC power plug.  The diagram supplied with the enclosure kit shows using a pin for ground that was found to have a no-connect.  The other unused pin turned out to be ground (the sleeve on the DC plug). 
Double-check your wiring in this area with a multimeter to ensure that 1) You have continuity where you expect it from power supply to the µbitx board, and 2) You haven’t inadvertently reversed anything or shorted anything out. 
Don’t forget the chassis ground to the solder tab that comes with the SO-239 socket.

Wiring up the Antenna connector

Dave used the supplied antenna 2 pin connector and wiring that was supplied with the ubitx, but it was not possible to keep it only 2 inches long in this enclosure.  It’s more like 4+ inches. You could use a short piece of RG-174, instead, to lessen any possible pickup of birdies.

Digital interfaces on rear panel

Dave hasn’t used the digital interface for the back panel or the front panel RX/TX LED.


Remote head for uBITx

The creative genius of µBITx constructors has no end.  This 3D printed version of a wired remote head for the µBITx was designed and built by Gel Vega DU2RK and is truly amazing.

The Remote Head incorporates a ring lit rotary encoder and ring-lit volume control, 8 pin microphone jack,  stereo jacks for headphones and key and a 3.5″ Nextion screen.    Now for a wireless version Gel