Warming effect of driver and pre-driver affects spurs

Lawrence Oberman mentioned an issue he has on a v4 board that looks like RF coupling or leakage when testing CW on 20m for FCC compliance.

He doesn’t see it with SSB but if the rig is placed on transmit for long enough spurs will start to show up .  He has only just got Axicom relays to replace the stock relays. Strangely enough he has not seen this behaviour on 15m, 17m or the higher frequency bands, or on the bands below  14MHz.

Others have seen similar phenomena on different bands, some with the spurs appearing on starting TX and then disappearing.

Allison KB1GMX says “Both cases come from the same source, heating in the amplifier usually the pre-driver and driver stages but it can include the finals. These stages are not thermally stable and parts heat up and their bias shifts.”


v5 board more sensitive

Ashhar Farhan VU2ESE tells us that the µBITx v5 board has more gain on transmit, as well as on receive, than the previous boards.  This is due to the BFR93w transistors in the 45 MHZ IF in place of the 2N3904s.

The carrier and spurs will be appear to be higher if the TX gain (controlled by RV1) is running flat out. it is best to reduce this to about 60% of the full gain. One way of achieving this is to connect a 50 mv audio signal to the mic, and transmit SSB on 7 MHz while reducing the power out until it is around 7 watts.


Using a 100 PPR encoder with the uBITx

Allison KB1GMX gives details on how to wire up the commonly available 100prr-6 encoder.  These have a nice vernier style dial and cover 100 pulses per 360 degree rotation.  The calibration points line up with these pulses.  They come with either 4 or 6 wire terminals on the back.

The A and B terminals have transistor outputs to ground and are used in connecting to the raduino:

  • Ground is ground (0V) terminal
  • Black and brown to the A and B terminals (reverse if the rotation direction is backward)
  • 5V from raduino 5V reg to the internal LEDs used in the optical encoder  (Vcc terminal)

Allison uses the V4.3 code in her µBITx with here own mods and this encoder worked well. Some firmware for the Raduino will not be sufficiently fast to keep up with the signals being sent from the encoder if you rotate the encoder quickly.

The uBITx.net editor likes the black version better.  These are a classy unit.


CEC beta release for v5 board


Ian KD8CEC has announced a beta version of his firmware (Version 1.12) for the uBITX V5 board.  He has written an article about it here.

All existing firmware functions for V3 and V4 are available on the V5 beta.

The same version of uBITX Manager will work with the v5 Board.

Only the LPF control and the frequency control part are changed in the V5 code.  Ian has released firmware V1.121 for V5.


Identifying your uBITx board

Alison KB1GMX counts 5 different schematics for the µBITx, and that is not including the HF1 or minima (2014) designs that came before the µBITx.  The design was evolutionary.

The first production boards were labelled “V3”.  Two further iterations have been sold since, the “V4” and now “V5”.

  • V1 and V2 models were prototypes, and were not marketed and sold
  • V3 had the TDA2822 audio chip in it.  One batch had issues, and would easily fail.  This was the first production board from December 2017.
  • V4 had discrete transistors for the audio section and test points were introduced in a number of locations on the board.  Pads were also included to allow the RD16HHF to be used to replace the, as shipped,  IRF510 finals.  This board had issues with low audio output – more suitable for headphones than speakers.
  • V5 changes the 12mhz IF local oscillator to 11.059 MHz, and uses the LM386 for audio.   The Low Pass Filter layout and relay arrangement has been improved to reduce harmonic removal.

V3 and V4 are probably technically not fully compliant with emissions regulations in most countries (at least in the developed world).   However, the low power output of the µBITx probably means that emissions will have resulted in few issues with interference in practice.

The effectiveness of harmonics, IMD and spur modifications incorporated in the V5 board have yet to be established across a selection of production boards.  There are no doubt improvements, but the degree to which the product could be considered to be 100% compliant on all bands and all modes has yet to be established.

[Edited by uBITx.net]



Spectrum analyser tests of v5 uBITx board

Jim Sheldon W0EB has done some initial testing of the new µBITx board on his brand new spectrum analyser.   The results are CW only (so these results won’t show the impacts of any distortion in the mixers or IF bidi amplifiers that were observed with the v3 and v4 boards.

There are still some bands that would not meet most countries’ spectral purity requirements.

For a full set of graphs for each band click on the reference link below.


History of designs leading to the v5 uBITx

The following list of circuit designs has been compiled by Tom KF5NWC:


A large group of enthusiasts worked with Farhan to create and test a general coverage receiver and multi-band transmitter called the Minima. Its simplicity, innovations such as its KISS mixer,  shuttle tuning using a potentiometer, and overall low build cost inspired hope of an affordable multi-band transceiver (to me anyways). 🙂

link to schematic

Ubitx v1

Continuing on with the general receiver concept with lessons learned from the minima, the uBitx was published.

link to schematic

uBitx v2

No schematics are known to have been published.

uBitx v3

The version 3 schematic is the version of the first production board from HFSignals.com (formally hfsigs.com).

link to download

uBitx v4

link to schematic on HFSignals

  • c210 and c216 – are listed as 0 pf and are not present on the board used in production by HFSignals.
  • Q942 and Q952 – are not populated on board sold by HFSignals. As sold by HFSignals, the final drivers for the PA are IRF510. These alternative pads allow experimentation such as replacing the IRF510’s RD15HVF1’s which are a different pinout.

uBitx v5

link to download

  • c210 and c216 – are listed as 0 pf and are not present on the board used in production by HFSignals.
  • Q942 and Q952 – are not populated on board sold by HFSignals. As sold by HFSignals, the final drivers for the PA are IRF510. These alternative pads allow experimentation such as replacing the IRF510’s RD15HVF1’s which are a different pinout.


For those who are not following the email list, during the gap in coverage on ubitx.net in January, Al and Jack launched their JackAl board that adds a lot of features to the µBITx.

The hardware is compatible with the µBITx v5 board, but requires different firmware.   More details on JackAl will be added to the website with a January posting date shortly.  Check back in the list of posts, as I am backdating information to provide a better history for constructors visiting the site.

Jack is going to be at Hamcation in Orlando. If you see a shirt with the picture of the JackAl display on the back at Hamcation,  then stop and say “Hi!” to Jack W8TEE.

Reference 1
Reference 2

BITeensio card beta firmware released

Jim Sheldon W0EB has announced that the Triumvirate Skonk Worx (TSW) has published their latest “beta” 2.8″ or 3.2″ Color TFT touch screen firmware for the BITeensio controller card. This new firmware addresses the changes Farhan made to the uBITX in the release of his Version 5 transceiver board.  This board is now shipping from HF Signals.

Using the BITeensio card in combination with the new firmware means constructors will now have the capability of selecting operation with either the older V3 and V4 uBITX boards which we are calling “Legacy” boards or the new Version 5 ones via an item in the “Calibration” menu.

Depending on which type of uBITX it is installed in, the  one time calibration will be required for that uBITX board.

Calibration data is stored on the BITeensio’s Micro SD card in different locations for the 2 different versions so if you calibrate the card in a V4 (or V3) radio, and later decide to switch it to a V5 radio, you will have to again calibrate it for the V5 system. However, once that has been done, you can then swap the BITeensio back into your original “Legacy” radio, select “VL” in the calibration menu and it will recall the previously stored calibration data for that version. If it’s the same VL board you originally used for “VL” calibration, you should not have to re-calibrate the card. If, however, you install it in a different uBITX than the original one, you may have to touch up the calibration to make things sound right and operate on the right frequency.  The same is true for V5 boards.

Since both of the displays (2.8″ and 3.2″) use the same ILI-9341 controller, and have the same number of pixels, no software changes are needed to change out the display. No user action is required to switch from one to the other except to make sure they are cabled properly and this is outlined in the manual.

The operating manual for this software has been completely re-written to reflect the changes and the pictures have been changed to show the operating information in the new version.

You can find complete information on this (and other items from TSW) on their website.