Reasonable heat output and the raduino regulator



Bob W4GHV asks how hot the regulator on the Raduino should get.

The Raduino has a 7805 regulator sticking awkwardly out of the side of the Raduino board.  Unsoldering the 7805 regulator and mounting it   on the reverse side of the board (facing inwards) can fix that little awkwardness.

The regulator also has another problem.  It gets hot!  It is fed with 12v DC input from the rig and produces regulated +5V for the Arduino Nano and the 16×2 Display unit.   The display itself draws up to 100mA.  The Nano typically draws around 35-70 mA, but it depends on exactly  what is connected.   The voltage difference between the input and output multiplied by the current is power dissipated in heat in watts (i.e. typically a bit over 1 watt).

The 7805 regulator can feel quite hot to the touch.   However, there is really no danger that it will get overheated at 12 to 13.8v input voltage and typical current draws from the Raduino unit.  Allison KB1GMX says however, “Keep it under 70C (168F) as the device has a thermal shutdown and it lives longer”.

You can share the heat around by installing a resistor between the 12vDC line and the 7805 regulator input. Skip, NC9O, added a 47 ohm resistor in the 12vdc into the regulator by cutting the trace from pin 15&16 on the Raduino. He used a  1/4 watt resistor, but calculations by others suggest a 1/2 watt or 1 watt resistor would be better.

The alternative is to remove the regulator altogether and feed the Raduino from a suitable 12v to 5v buck power supply (obtainable off eBay or Aliexpress for very little outlay) or set the output of the buck power supply to just over 7v if you can’t be bothered removing the 7805.    For those of us thinking about touch screens, this makes quite a bit of sense!


Biteensio production boards have arrived and available now

Jim  W0EB has announced that the Biteensio production boards have arrived and been checked out.  See for details on how you can order one of these.   Remember that Vince K8ZW was the winner of the competition to name these boards.

Jim also has some breakout boards for the 1/8″ jacks that will allow them to be easily mounted and wired up without having to guess which terminal does what.  These may save a lot of grief.

Key features of this board include:

  1. uses the PJRC Teensy 3.6 as the MPU rather than the Arduino NANO
  2. plugs into the 16 pin female header on the uBITX main board just like the Raduino and the RadI2Cino
  3. the main tuning encoder, function switch and push-to-talk wiring will still be compatible with both the Raduino and the RadI2Cino.
  4. All of the extra, available I/O pins are brought out to DuPont pin headers (some on the front and some on the back of the board)  

See the board installed on the µBITx main board below:


Prices are $12 (USD) for the bare boards to domestic US customers and $16 (USD) to international customers.

Kits which will include all parts except a Teensy 3.6 MPU, will be US$35 to US customers and US$45 to international customers. This price includes shipping (both domestic and international).

PayPal will be the preferred payment method and the ONLY payment method for international customers.

Download a copy of the BITeensio Board Construction Manual. Up to date versions will always be available in the “Documentation” directory under the W0EB/W2CTX uBITX Files link on this page.

For other details see the W0EB website.

Note that the Biteensio is not compatible with the manufacturer’s firmware supplied with your µBITx or the CEC firmware from Ian KD8CEC. The Biteensio board uses a different keying system and a different processor (Teensy 3.5 or 3.6), so you will need to use the W0EB/W2CTX firmware supplied especially for the Biteensio.


Buy your Nextion display now!

If this display looks like it is from a commercial rig, then you are wrong!  It is  the Nextion display mounted on a µBITx!

Ian KD8CEC will shortly release his newest enhancement to CEC firmware.  His latest modification to the CEC firmware supports Nextion screens. This was foreshadowed recently on the BITX20 list.


If you want further proof, check out Ian’s recently prepared youtube video of the Nextion screen in operation.  His release is imminent.

Get your order in for a Nextion display immediately, as they are likely to sell out when 6000 µBITx owners twig that they really do NEED a Nextion display.  [Note that has no relationship with ITEAD – who make the Nextion!]

Why Nextion?

There are some very good reasons why the Nextion display is the way to go:

  • Nextion screens make it quicker for developers to provide a user-friendly interface to their product:  a separate processor controls graphics on the screen, and a Windows WSYWIG emulator can be developed for free to whip up a User Interface for the Nextion display.   The processor in the Nextion has its own control language and coding that is similar to C++
  • Users can easily hack their own display’s look and feel, by plugging into a standardised protocol between the screen processor and main processor that are connected via a standard serial port.
  • Screens come in a variety of sizes from 2.4″ to 7″.  Resizing of images and buttons is all that is required to make firmware work on a different screen size. No coding is required.  Software required is simply the Nextion Windows software and a graphics programme (MS Paint is adequate).
  • The screens come in two varieties:  a BASIC model and an ENHANCED model.  The ENHANCED model has GPIO lines controlled by the display processor and a Real Time Clock (RTC).

Nextion display units cost more than other displays for a reason.  The independent processor removes most of the burden for screen manipulation from the main processor, and it is much quicker and easier to develop the user interface and to customise it for different sized screens and to add/subtract features.   Nextion displays also include a microSD card reader.  They run on +5v DC and include a serial port.   Note that the Enhanced Model contains a battery mount for the RTC, but does not include the battery (CR1220) itself.  This is not required until you want to use the RTC.

How easy will it be to use the Nextion Display?

It will be VERY EASY to add a Nextion display to your µBITx.  Watch the video!

No hardware modifications are required to your µBITx, but you will of course  need enough front panel space to install your colour touch display of choice.  You may even need a bigger case if you want to install the 7″ Nextion display!

You will also need to download two new files:

  1. an updated version of KD8CEC’s firmware, that incorporates the interfacing protocol to the Nextion for installation in your Raduino.
  2. an image file (firmware) for insertion in the Nextion display unit.

The downloaded firmware for the Nextion needs to match with your screen size.  There are two variants for each screen size:  a BASIC or ENHANCED version of the Nextion display unit (see the discussion on which version to buy below).

This firmware needs to be saved to a microSD card (a 2GB or larger card is required).  Insert the card in the Nextion display and in powering up the Nextion display will automatically load the firmware from the microSD card into the Nextion flash storage.   Remove the microSD card when the upload is complete.

Four wires connect the Nextion display to the Raduino.  Two lines are for power, and the other two are serial RX and TX that connect to standard IO ports on the µBITx that were used for the 16×2 standard display.

Reboot your µBITx and your Nextion display should be working!

What to look out for when buying a Nextion Display

There are two versions of the Nextion Display – one developed for the Chinese market and an English language version that supports the Nextion Windows development environment.  Make sure you don’t get the cheaper, but incompatible Chinese version.  Look out for “English Version” in the marketing blurb.  This won’t be an issue if you buy from the developer (ITEAD).

 I understand a downloadable hex file will be available that works the same as the English version, for those of us who purchased the wrong model in error!  Thanks to Ian, who did it blind (also not being able to read Chinese)!

Any size will work with the CEC firmware on the Raduino end.  However, Nextion firmware is specific to  either the BASIC or ENHANCED version of the screen and to the resolution of the screen.   That said, any version can be modified to work with any other screen size with just a little bit of work on the part of the user.   You can also fully customise your screen to meet your own requirements.  Change the colours, or change the entire look and feel.  No coding is required to do this, just cut and paste the code from the supplied CEC version for each tool.

Purchase the ENHANCED model of the Nextion (for a few more dollars) if you think you will use the GPIO or RTC features in future.  The RTC could be useful for digital modes that require precise timing, or for satellite work, etc.  Additional GPIO lines could solve one of the problems with the Raduino:  a lack of spare digital ports to support customised add-ons.  For example, if you want to add 160m and switch in an additional LPF, or  if you are worried about potential spurs, you will be able to pull in bandpass filters for the high bands. In these instances you may want to spend a little more to get the ENHANCED version.

If you don’t want to wait until firmware is available for your screen size, then purchase a 2.4″ or 2.8″ BASIC or ENHANCED Nextion Display now.   These two screens have the exact same resolution, and the default version of the Nextion Firmware from Ian KD8CEC will work on both screen sizes without modification.

If you already have a different sized screen, or want to buy a bigger screen, right from the outset, don’t panic.  You may need to make some adjustments to the firmware yourself.  This is not difficult – but involves resizing graphics and moving around objects to suit the larger screen area/resolution.  Some of us are working on modifications to the Nextion firmware to accommodate 3.2″ and 3.5″ screens. Firmware for these screens is likely to be available quickly.

Screen sizes and resolutions for the BASIC models available on ITEAD’s website are as follows:

The ENHANCED versions available from ITEAD are as follows:

Most of us will choose to buy our Nextion displays from Aliexpress or eBay.

They are available in all sizes and in either BASIC or ENHANCED versions.  It is unclear which are OEM versions and which are clones.  It probably doesn’t matter.

Look for highly rated suppliers and those with higher shipping volumes.  The biggest risks are that your screen arrives cracked, or simply never arrives.  You will need some form of redress when goods arrive in a damaged state or simply never arrive, and this is where the intermediaries in eBAY, Aliexpress or Paypal can assist.


Quadrature output from si5351a

The SI5351a is a key secret to the success of the BITx range of transceivers.  This chip puts out three PLL signals for the two local oscillators and the VFO in the µBITx.   Without this chip (or something similar) a double superhet design such as that used in the µBITx would require considerably more complexity, with either an analogue VFO that was prone to drift (as in the BITX20) or a PLL circuit that added cost and complexity.  The Raduino integrates a 16×2 line display along with an arduino nano and the SI5351a chip … prebuilt for US$25.

So along comes Miguel PY2OHH who announces that he as designed a new
VFO using the SI5351 and Arduino nano, which produces an output  “in quadrature” from 4.76 MHz to 220MHz.  This means is has two outputs on the same frequency, but which are 90 degrees phase shifted from each other.    Note that there is also a small frequency window that can’t be used between 144.66 MHz and 150MHz.

You can read all about the idea, and see a prototype VFO here.

So why is this such a big deal?

What you may not know is that a quadrature mixer, which requires two signals from a local oscillator fed at 90 degrees from each other, is at the core of most SDR receivers.   In an SDR receiver, there is very little “front end” analogue circuitry, with signals rapidly routed to a processor in digital form to apply filtering and band-limiting.    Miguel’s breakthrough paves the way for simple, low-cost SDR transceivers that are of low cost and high performance.   We know that Ashhar Farhan VU2ESE has said in the past that he is experimenting with SDR designs (and with a VHF/UHF version of the BITx).   Let’s hope this innovation spurs him on to produce a stunning new SDR design in kit form!


A model build with PA mods, AGC and anti-pop mods

Mike N6CMY enjoyed his first build of the µBITx so much he built another one! This one avoided all of the mistakes of the first build.



1. Choke in series with R86.
2. All emitter resistors in buffer, predriver and driver bypassed.
3. Feedback resistor in PA increased to 600 Ohms.
4. Output Xformer replace with 2:4 on BN43-202.
5. Adafruit audio compressor in mic line with chokes to eliminate RF feedback.
6. PA powered by buck boost at 13.8V the rest of the board by 12V battery.


30W on 80 and 40, 20W on 20. RV1 adjusted to reduce output to 15W.


1. ND6T AGC installed (underneath main board) at K3 powered by 5V regulator.

2. Additional stage of audio gain installed between Q70 and U1 to make up for loss due to AGC.


Plenty of audio!! and good AGC action.
3. VE1BWV audio pop mod (similar to the one standard on the new ubitx) installed underneath the main board.

4. To further enhance the pop suppression PIN 1 at K3 is grounded.

RESULTS: Sounds fine to me.


A red/green LED TX/RX LED is installed on front and a TX/RX relay to key an external PA is installed on the back.


Evening up power output – interim suggestions from Allison KB1GMX

Allison KB1GMX has provided an update on her experimentation with flattening out the power curve on the µBITx.

Gain and power line up with a few possible solutions listed:

Mixer – output at full tilt about -10 dbm. Go higher and the spur gets bigger so lower output here is better.

Q90 – no mods at 80m about 16db at 10M about 10-11db and not more than 3mW power. Replace it with a really hot transistor. BFR106 has a FT of 5ghz and can do over 100mW. This should keep the stage gain at about 16-18db from 80 through 10M and deliver the 3mw! It is the easiest stage to make flat and high gain as this get more difficult at higher power out.

Pre-driver – takes that 1mw and boost it to about 40mw, We hope. What she saw was about 45mW at 80m and barely 8mW at 10m . Note the gain at 80m is about 16db and at 10m maybe 9db.

We need the gain again to be more stable and higher as well. Transistors tried that worked better included the TO18 2n2222A, 2n3866, and 2n5109. The 5109 was best even though she used only one. Second best was tie between a single 3866 and two 2n2222. MPSH10 was disappointing.

Allison plans to try an oddball 2n6661A, [at 14$ each most will choke] a VMOS fet has potential and requires many circuit changes[Bipolar bias to MOSFET]. They worked really well in another project at VHF.

Driver – takes that 40mw and make about .4W at 80 and sinks to barely .08W at 10m. Gain for that stage is supposed to be about 16db and likely is at 80m but at 10m measured for different 3904s from around 8 to 11db.

This is where the 2n3904 really fails. Its bandwidth at high currents actually does down. The 2n2222A has the reverse, the gain and bandwidth increased with increasing current. While not an ideal part it does work better. The ideal parts here would be two devices in push pull [not 4] and with higher FT.  Allions hasn’t yet tried 5109 parts here but its a solid bet. She wishes 2n3553s, 2SC2166, 2SC799, 2sc1306 and others were still around.

She plans to try an oddball 2n6661A here too as its good for up to 6W.

Finals IRF510 at 80m approaches 15-20W with a gain of over 17db, at 10m its about 13db, but the drive is so low that yields maybe 2W.

If there is enough power at the gate it does the job we ask. RD16HHF does not offer more gain or bandwidth as MOSFETS do not have the equivalent of FT.  These parts do offer a handy tab that can be grounded.

To go from -10 dbm[.0001W] to +40 dbm[10W] we need 50 db of gain over all. That includes losses to transformers and other circuit features. So we need more gain than that available.  Maybe 6 to 10DB more gain would allow some latitude on the gain adjustment pot.

So with four stages and the last being limited to the IRF510s. We set a few rules.

  1. We never run a transistor wide open as one may exceed and another fall short.
    For 2n3904s that happens and the lowest common denominator for them is around 10db. Use better transistors and lots of feedback. More likely to work for everyone than a bet on Monte Carlo.
  2. We only have four stages! The board is laid out that way. Reality sucks.
  3.  IRF510 or RD16HHF you get about 13-16db of gain, period. More
    is wishful thinking or running wide open and risking stability. Hint IRF510s blown cost about US$2, RD16HHFs blown cost US$10. Going to IRF520 and 530 are not better [for 10W output] as the internal capacitances are significantly higher and these parts don’t make the job easier.
  4. Based on total gain needed and what the finals can be reasonably expected to do: The three prior stages must deliver 45 to 47 db of gain. Its also a lot so attention to stability is everything.
  5.  The result must be stable. Oscillation will kill the finals.

As it turns out, item four is the killer as its basically asking for 16db from all three stages. You need good parts for that. Also the interstage coupling must be up to the job while not introducing uncontrolled losses. This is a tall order. So far I have only partial answers.

Answers so far:

Dump the 3904s and use 2n22222(TO18), for those interested in 80-17M it works remarkably well and give a boost up high too. If you go to 2n5109s you may need one as pre-driver and 2 in the driver stage.  They are big and the space is small.  Use the SHORTEST leads possible.

Replace or parallel R941,R911, R96,R942 to get 11 ohms each (I paralleled 22ohms across them).  Lower emitter resistance helps  the gain and power out to finals.

Replace Q90 with BFR106.  Note R81 has to be increased to between
2K and 2.7K for this part. (for those making suggestions I tried 2n2369 in
SMT, it was better but not great). Mouser has the BFR106 for a whopping 38 cents each.

Change C81 to 470 pf, This flattens the 80 and 40M runaway power and helps the higher bands.

There are many changes to transformers possible but for the moment the above are best bang for the buck. Also changing the transformers might be a handful for some.

Warning every time I tried the 2:4 turn transformer with any ferrite the finals were heating a lot and the stage efficiency was well under 40% [terrible with IRF or RD16]. The 2:3 was better at high power but below 50% efficent. This is still in the grinder…


Latest release of the TFT Colour Touch Control from VU2SPF and VE1BWV

VU2SPF and Joe VE1BWV have released the latest version of their TFT Colour Touch Control.

Low cost, standard easy to get parts, Colour, Touch Control and any combination of Touch Control or physical buttons.

TFT (Touch) Display module, Atmega 2650, Si5351 DDS, 1 UBITX and a few wires = All Band rig with Computer / Radio Touch Control Colour Display.

Some new features:

  1. Automatic Scanning – up to band edges in both the directions is now added in V2.9bU of software. The scanning allows one to find signals of interest across the band. Two small buttons labeled ‘U’ and ‘D’ scan in up and down directions from the currently set frequency. The scanning can be stopped by touching the frequency display area.
  2. CAT Control  – the software now has new code to emulate FT817 Cat commands… This provides radio and computer control for the digital modes.
  3. User Manual   A new comprehensive user manual has also been added. Various users and new builders have been looking for this for quite a while.The new version is available on Github at : also available at:

(UBITX ver2.9bu Installation Results)

Note that at present the firmware doesn’t support CW.