Evening up power out using KB1GMX and K9HZ solutions

Mike N6CMY has been doing some mods on his µBITx, including some of Allison’s mods by substituting 2n2222’s and a BFR106 for the 3904’s on the RF lineup (pre-driver and driver stages).

In terms of output power the results are impressive. But in terms of levelling  up the output… well not so good.

Mike measured 12W on 10M and over 35W  on 40M!  He was a bit taken aback at this point!

He finally bit the bullet and used K9HZ’s multi relay/pot method for levelling the response.

Mike was reluctant to use such a brute-force solution for a subtle problem but he now measures 15W on 80, 40, 20 M and 12 on 10M. VICTORY!!


A fan for your uBITx

Arvo KD9XLC has put one of these 12v fans that cost less than a dollar on the back of his Excelway case from Bangood (which apparently now on sale for $8.88).

You could attach the fan to the cabinet with hot glue, or use the correctly sized bolts/nuts.

And if you don’t want those fans to run on receive connect them to the TX 12v line, namely at pin 3 on U2, which is what Arvo did.


JJ1EPE has had a uBITx article published in Japanese CQ Magazine

Akira Horie JJ1EPE  has had an article published about the µBITx in the 19 June edition of the CQ ham radio magazine of Japan.   

The magazine is of course in Japanese.     Akira’s article covers:

  • A helpful  website (www.uBitx.net) 
  • Helpful firmware, particularly Ian KD8CEC’s firmware
  • Instructions on how to upload the firmware to the µBitx.
  • How to obtain certification of the µBitx from the relevant Japanese authority.

Gaining certification for a home-built rig is not straight forward in Japan and involves:

  1. Ensuing the µbitx cannot transmit outside of the ham bands approved for use by Japanese amateur operators
  2. Suppression of spurious harmonics to meet Japan regulations, for instance by using an external LPF and/or tuner.

Akira has the all important certification and  license to use his µBitx from the relevant Japanese government authority.

He is now enjoying QSOs on his µBitx!

Adding a keypad to your uBITx

Arv K7HKL asked whether anybody was interested in adding a keypad to their µBITx and got quite a few responses.  It seems that there are a few interested in the same idea!

Jack W8TEE says he would use an analogue approach but this requires lots of spare digital I/O ports that simply don’t exist on a standard µBItx.  So what choices are there on a standard µBITx with just one spare analogue port available (A7) on the raduino board?

The choices are simple, you could use:

  1. An i2c expander port (we’ll ignore this suggestion for now)
  2. A matrix keypad with resistor array fed into the single analogue port on A7 (a bit like how the keying is done on the µBITx)
  3. An i2c keypad.

Matrix keypads with resistor arrays

In terms of matrix keypads there are plenty of choices from simple “rubber” keypads, through to expensive and solid keypads.  With a choice of 12 or 16 keypads, you may want to think about the options carefully.

Some only have numbers, others have blank keys that allow for customisation.  For example, you can replace the blue bits of paper on the  Robotdyn keypad with your own printed symbols or numbers:

The keypad illustrated  above does not require a resistor matrix as it is built in to the module.

i2c keypads

As it happens Robotdyn also make a handy capacitive i2c encoder board that has a matching capacitive keyboard.  If you do decide to use an encoder board with the TTP229 chip on board (like the Robotdyn board below), then you should note that there is a hacked sketch that directly works with the board via any 2 ports using bit-banging, as well as a sketch that uses the Wire (i2c) library.  A useful reference article can be found here.

[ubitx.net has no interests in Robotdyn!]


Probably the i2c approach would be the preferred approach for most constructors as it does not require using up the last available analogue port on the Raduino.   Constructors generally like to save this port for essential analogue functions like a digital S-meter and Power Meter.  Regardless of which method you use, you will need to leave aside clock cycles to montior keys being depressed.

Both approaches will require some simple coding changes to be made to the  firmware.  We will be waiting to see the firmware release from Arv!

By the way, here at ubitx.net we won’t be installing a keypad. There is a very nice and practical virtual keypad (thanks to Ian KD8CEC) provided for free in his Nextion display code.  A frequency can be easily dialled up or you can switch to another band, right there on the Nextion screen.


uBITx in an aluminium briefcase

Aarne Haas WY7ATH has just finished a µBitX build in an old ‘toy’ briefcase.  It makes for a good enclosure – along the lines of µBITx builds in P cases. There is a small manually switched fan inside blowing on the final heatsinks when operating digital modes.  Nice one!

Nextion Displays – Hints for loading display firmware


Michael VE3WMB brings us some hints when installing Nextion displays:

1) The Display wants the microSD card to be formatted as FAT32.   Make sure your microSD card is no larger than 32GB

The default in  Windows is to format cards > 32 GB as exFAT, which the Nextion will not accept. In fact Windows 10 probably won’t even let your reformat a card this big as FAT32.  (I am sure if you dig deep enough there might be a way to do this. I am not a Windows GURU).

Currently you only need a 2 GB card,  so if you need to buy one for this purpose try an 8GB card.  It is also worthwhile buyong a brand name card (like Sandisk).
Some no-name cards are slower than cold molasses to read from and write to.

2) If you have a problematic microSD card, when you power up the rig you might not see anything on the display, not even a backlight !  

I spent considerable time trying to solve what I thought was a wiring/power problem to the display when it was a bad SD card. When the I removed the card and power-cycled the rig the Nextion display came up fine with a demo program that was already loaded.  So my recommendation is for the initial power up of the display don’t insert the SD card. That way you can be sure that you have it wired up ok before you start messing with SD cards.

3) Beware, ground and +5V connections on the Raduino going to the Nextion Display are adjacent to each other. 
I recommend that you check and recheck your wiring several times before applying power.  It is very easy to accidentally swap these and you won’t be happy if you do.  As they say, “An ounce of prevention is worth a pound of cure”. One group member has already found this out the hard way.

Mark AA7TA adds:

4) Duplicate .tft files (including hidden files) will cause grief on the Nextion

You may get a message on the display that the load failed because there is more than one .tft file on the SD card.  This can happen even when you look and you see only one file.

You need to be sure to enable viewing of hidden files in file explorer (Windows) or finder (on a Mac)… There’s probably one hiding there with the .tft suffix that you need to delete.  I don’t think either operating system will show hidden files by default. The same goes for Linux.

Mark notes that a 1G SD card is plenty big enough for the current tft file.

Keven adds, “Linux doesn’t show hidden files by default.  But you can see them by typing:

ls -al

in a terminal window when you’re in the directory you want to examine.  To hide a file, rename it with a dot (‘.’) as the first character.”

Mike ZL1AXG adds:

5) Make sure you install the screen the right way around

Power up the display before you start making holes and check the orientation of the display and that the screen is functioning correctly.   As with the 16×2 display, it is possible to install the display upside down by mistake!  Given it is not symmetric (there is a wider bar to the right hand side of the display) care is needed!  The inner silver line on the screen defines the touch sensitive boundary.  Cut your hole so that the screen fits so the line is just visible around the outside edge.

Dimensions of Nextion displays can be found for this zone on the itead website. Click on your display and near the bottom of the page you will find a link to the screen dimensions.

6) For most people the 3.2″ screen or larger will be best

A 3.2″ screen is only just big enough to feel comfortable for us fat-fingered chaps.   It is also just wider enough to reuse the width of the 16×2 screen.  Smaller screens inserted in the space where the 16×2 screen currently lives will require an additional aluminium or plastic plate to be added to the front panel to cover the existing width of the 16×2 screen.


Definitive audio pop fix

With the release of the v4 board from HF Signals, we finally have  a design for an audio pop fix that can be applied to the v3 µBITx board with few additional parts.

Mike ZL1AXG has completed this mod and can vouch for it have removed all unwanted pops (on both transitions from RX to TX and TX to RX). It doesn’t kill the CW sidetone.  His application of the mod is described below.

The mod can be placed in the same position on the v3 board as in the v4 design,  using a simple Dupont header as shown below, but there are other ways of achieving the same result.

This mod only involves 5 parts.   It is now the uBITx.net recommended mod to fix the audio pop.  The audio pop fix summary will be updated shortly.  All other fixes are now effectively redundant because they are more complex.

NB – This is an extract from the circuit diagram on hfsignals.com.  There is an error with the numbering of the leads on Q74.   Check first, before wiring up!

Parts required are:

  1. 2n7000 MOSFET or similar (Q74)
  2.  1 µF ceramic capacitor (C79)
  3. 1N4148 or similar silicon signal diode (D14)
  4. 100K resistor (R78)
  5. 1K resistor (R70)

Complete the following steps:

  1.  Locate R70 (100 ohm) resistor on the right hand side of the board when looking from the front panel and remove this resistor.
  2. Drill a small hole through the board roughly in line with the two solder pads for R70 in front of the relay 7/10 of an inch to the right.
  3. Install a standard dupont female header with 7 sockets (spacing 0.1″ per pin) on to the board (see first photo above).    The first two pins are bent over at 90 degrees and solder to the pads for R70.   Pins 3-6 are removed.  Cut them off underneath and then pull them out with a pair of pliers.    Solder the final pin 7 underneath the board
  4. Install parts on the  plug in board as per the circuit diagram below, and use a male dupont pin  to connect to the T-R line.  Plug the board in to its socket, connect the T-R line, and you should have a nice quiet transition going to TX.
Step 1 & 3: Install the dupont header to replace R70. Pins 1 & 2 on the left are bent over at 90 degrees and soldered to the pads. Pins 3-6 are removed. Pin 7 passes through a new hole drilled in the board
Step 2 – Reverse side showing pin 7 soldered to the underside of the board to securely attach the female dupont header above
Step 4: Install the components on a small piece of perf board. The purple wire connects to the T/R line on the raduino.

New graphic for uBITx.net

Some of you will have been sufficiently observant to notice that the graphic at the top of the www.ubitx.net webpage has been updated.  This is because Mike ZL1AXG has installed a Nextion 3.5″ touch screen on his own µBITx.    Careful work with a drill and file will yield satisfying results.

He also installed the latest pop fix from the v4 board (see the separate article).