Some interesting cases

Finding a case for your µBITx is easy … finding a good case is more tricky.  Many use one of the many µBITx cases sold by Sunil.  Others have their own favourites

Two new suggestions from Jack KZ5A are worthy of a second look.

The Cheval case illustrated below can be obtained in both steel and aluminium versions (we would strongly recommend the aluminium version).  This case will have to be imported from Thailand.  It is also available on eBay.  It is a very nice looking enclosure, reminiscent of Heathkit enclosures from the 1970s.

The Circuit Specialists aluminium instrument enclosure is a not quite as good looking enclosure, but at a very good price ($US21 excl shipping).

Mike ZL1AXG purchased several aluminium cases from that are intended to house stereo amplifiers.  This particular model (Breeze 2207) is 228mm x 70mm x 215mm.  A good size for incorporating a few additional circuit boards alongside the µBITx main board. These cases are precision made and look really nice.  They can be acquired for around US$15 each (plus shipping – that will be more than the cost of the enclosure).  Mike has yet to transplant his µBITx into the new case.


Switching AGC delay settings with ND6T mod

Derek G4VWI has used a sub-miniature MIL spec rotary switch to switch between common, off/slow/fast as per  the ND6T wiring diagram for the Kit Projects board.

A screened pre-made wiring loom helps ensure the exposed sections are kept nice and short. Derek suggests choosing good quality connecting wire and pre-soldering the pads before tacking on the leads for best results.  He believes that this is by far the easiest AGC board design to fit.


Battery power for your uBITx

Pop VU2POP has added a LiPo battery inside his µBITx case as illustrated above.  He says “I installed a homebrew 3S2P li-ion battery pack into my ubitx cabinet.  I had planned my cabinet for the right space & fit.  Now I can carry my ubitx for outdoor  action!”.


ALC and alternatives for controlling your linear output stage

Ashhar Farhan VU2ESE observes that ALC is just one way of controlling output power from a linear amplifier stage and that an easier approach is to do it in software.

This needs software that can control the ‘mic volume’.  You could set the value differently for each band.  There is another pay-off with software mic gain, it can make a major difference to the transmit IMD.  At voice peaks, the tx linear chain compresses. The gain is not constant between low and high levels of modulation. This is the cause of in-channel IMD.   Now, if we have a look up table that amplifies the peaks more than the lows, we can ‘correct’ the gain back to being linear. This simple concept goes by the name of ‘pre-distortion’ in the SDR world.


uBITx and WSTJx

Don KM4UDX lived with  with non-trivial frequency/calibration error until (in his words he, “finally found my boy-bits and went back to reading everything ever written on uBITX calibration (with CEC firmware and memory manager). The result was extraordinary levels of fear and confusion.”

In desperation, he said “foo it” and calculated the error ratio @ 10.00 MHz, multiplied that ratio by the base calibration number to get ~~-5000, then added -5000 in Memory Manager, and hit reboot.

Then he went to wsjtx’s freqcal mode to measure his new error relative to 3.330 (-7Hz) and 10.00 (-18Hz) reference signals.  He was now close enough that he didn’t want to touch anything.

But of course he did… And every time he tried to reduce the error further by tweaking the calibration numbers, everything got worse. So he quickly realised he was as close as a mere mortal could aspire.

But he did run the complete freqcal process in wsjtx.   That process reduced his µBITX freq error to 1hz or less in wsjtx.   Don says , “That wsjtx is wicked. If anyone wants help with uBITX wsjtx freqcal mode, I’m your dude.”

Here are his wsprnet results using the humble v4 µBITX.

Don says,  “That was without any real effort other than stumbling in the dark, and GREAT help from fellow hams and wonderful persons”.

He is now ranked ~155 in 2 way WSPRnet spots after only a few days of auto band hopping.

“NEVER did I expect my little uBITX to get to Australia and Antarctica” says  Don and he adds, “All hale the mighty uBITX.”   We might all agree!


Long distance uBITx contact at 18,000Km

Ron K0EIA gives a quick love note for the µBitx …  He recently worked Andy VK5MAV/6 with just seven watts on his µBITx.   Ron heard Andy coming through loud and clear, with really excellent receive reception on his radio. Andy is a top notch operator and took my call split in traffic.  He was activating some island off the west coast of Australia (OC-211 according to website search).

He definitely did his part; I have a very quiet listening location; and my antenna is doing most of the work … but still an exciting QSO to log.

7.005MHz CW, uBitx v5, only mods are RTLSDR tap on 45MHz first IF, and N6DT AGC. Ant = fixed two element wire beam at 65ft.

Control CW TX power by unbalancing the second mixer

John (VK2ETA)  has been working on a successful modification to get the clock #1 mixer to unbalance on CW key down.  This involves the following steps:

1. Re-wire the T4 transformer input and output as per T2. That means as Jerry said to “… cut traces to T4 pins 3,5 and 6.  Swap them so T4 pins 3,5 are in from R47, pin 6 is out to C211.”

2. Disconnect (cut trace) from R105 to the common connection of C10, R27 and T2 (3,5).

3. Connect via a wire the disconnected side of R105 to the common connection of T4 (3,5), C211.

John used an audio shielded cable, and passed the wire under the board by drilling two small holes next the two connection points to ensure minimal pick-up of RF.

Pictures of R105 trace cut and wire to T4. (partially obscured by the hot melt glue on the toroids as I use my rig /P and /PM).

Picture of T4 traces swapped and cable from R105. (The line from the yellow toroid is a hot melt glue filament, not a wandering wire..hihi)

4. Change the software.  When in TX CW mode, disable clock #0, generate a clock #1 at “SECOND_OSC_USB” – “usbCarrier” = 45Mhz (+ or -) and clock #2 at (that same 45Mhz signal + target Tx frequency).

The difference in signal strength between key-up and key-down as seen on a control receiver is from way below S0 to S9+20dB or so, giving a dynamic range of over 70dB (indicative value in light of the basic test method).

The output power in CW mode can now be controlled finely by shifting the 45MHz clock slightly along the slope of the Xtal filter. For example I go from 14W max to between 1.5 and 2 watts by shifting the clock #1 frequency by 30Khz on the 20M band. On the 10M band, I need a shift of about 10Khz to reduce the 8 watts out to the same level.

Now, thanks to a bit of programming, John has full control of SSB as well as CW power across all bands. Great for his built-in ATU.

If someone with a spectrum analyzer could check the implications for the harmonics and spurs that would be a plus. John would expect in CW mode that the harmonic for 80, 40 and 30M bands would reduce, but some spurs to appear since we have the beat of two clocks now.  If there is interest John could modify Farhan’s code to match that modification (or publish some code snippets).

By the way, before he  did the mod above, he also tried to put a trim-pot between R105 / Ground / slider to T4 (3,5) and even when turned all the way to zero (slider to ground) it would still constantly unbalance the clock #1 mixer. So the change in topology as described above is the only way he could get it to work as intended.


Using a remote head on a uBITx for mobile operation

Dexter ZL2DEX posits that a uBitx is a bit difficult to *really* remote.  Its control and display are done by Arduino, but the unit supplied by default in the ‘kit’ has that as the ‘Raduino”, with the ‘VFO’ part of that, being the on-board SI5351. This puts RF generation at the ‘control head’, so any distance of ‘remote’ has to be minimal.

The solution, it would seem, is a homebrewed Arduino control, where the SI5351 can be controlled by the likes of its I2C-bus connection.

By this means frequency control can be a non-critical function, with distance achieved digitally: 3 wires (2 active and earth) which do not behave as transmission-lines needing such radical shielding (and can even be optically-isolated)!. This leaves Audio (By ‘dongle’?) and PTT/Keying (likewise able to be opto-isolated but also perhaps able to be encoded into the I2C bus?). Some (most?) of these modifications are already being worked on.

It’s only a short step from the above to full-USB or HDMI – or LAN/internet. Who needs megabuck rigs or even an SDR to get a remote head?

Ted K3RTA’s first attempt at establishing a uBitx with a remote head in his vehicle was with the original 20×2 LED screen. He extended the volume, tuning & function knob, and the microphone, along with the LED screen by means of a 25-wire printer cable. The Arduino/Raduino stuff remained with the mainboard in a box under the passenger seat.

The current model uses a 2.8″ Nextion LCD screen on a 4-wire shielded keyboard cable so I can see it at dashboard height. One could have run the rest of the controls to the same location.  However, the screen data nose gets hard to isolate… and Ted wanted the finger controls at a convenient arm-rest position rather than at  a reaching position.  There’s also one less microphone cable flopping around right in front of other things.  The tuning/function knob and other controls are, therefore, located in a separate control head that’s fed with a separate, VGA monitor extension cable.  The VGA cable is a Cheap-Old-Man compliant solution.  Better yet when it originated from a supply that Ted didn’t pay for in the first place. The variation and complexity of so thin a cable makes it ideal…  though an accidental discovery more so than a plan. Ted was just looking toward the shielded, 15 wires inside!

A VGA cable has four separate, shielded paths along with some extras, all shielded again by the outer layer. These can  protect the audio path.

Ted can still hear some of the Nextion activity, chiefly the data streams associated with the 2nd Nano and spectrum/s-meter action.  This is mostly on  weaker signals with the volume control turned right up.

He found the speaker audio, even with a Motorola public-safety type radio speaker,  a bit mild for 70mph highway use so Ted is adding a 15-watt amp to make it louder.


Adding SOTABEAMS variable bandwidth filter to your uBITX

SOTABEAMS make a  Digital Variable Audio Filter Module  that could usefully be added to your uBITx.

Dennis KG4RUL has developed an Arduino sketch for the SOTAEAMS Vari-filter which includes a nice display.  It utilizes a USB Nano V3.0 ATmega328 16M 5V Micro-controller CH340G board, or similar, available from Amazon and other sources and an OLED display module such as the HiLetgo 1.3″ IIC I2C Serial 128×64 SSH1106 OLED LCD Display LCD Module for Arduino AVR PIC, or similar.
Dennis is happy to share his firmware, but cannot offer any support – so please do not contact him for support.
You can download the sketch and a schematic, in PDF, from the SOTABEAMS website:
An additional document supplies information for linking a microcontroller with a SOTABEAMS, VariBeam (VB) module for use with a BITX/uBITX.  You can access this file at the following URL: