LED power out indicator

Lee  “I Void Warranties” N9LO ran across this circuit when looking for a transmit indicator for his Small Wonder Lab PSK31.

[Note the circuit was originally drawn incorrectly, but has now been updated]

Lee threw it together (there are not many parts) and it lights up bright and solid for CW and you an watch your modulation on SSB.   I can really see the difference when I switch in my SSM2167 module.

Jerry KE7ER recommends placing the circuit before the transmit LPF, not at the antenna port.   The diodes potentially create a bit of harmonic content that the LPF’s would remove.


KD8CEC firmware hint – CW frequency display

The KD8CEC firmware provides a lot of customisation features through uBITx Manager software.  Many user of Ian’s firmware are not aware of all the built-in features of his firmware.   This is one such instance!

JJ1EPE raised a concern that his display in CW mode was “off frequency”.  Well, it was from his perspective, but then the display was all the time showing the TX frequency not the offset frequency where the station he was listening to.

CW offsets create headaches in how you represent the frequency on a display.  In SSB the frequency you see on the display is the frequency of the suppressed carrier on receive and the same on transmit.   If you tune to the carrier frequency of a received station you won’t hear anything.  To get a sidetone we have to tune off the transmit frequency by a few hundred hertz.  Most people have worked out how to set the offset on the uBITx.

The standard that Ian KD8CEC has applied is to always show the TX frequency  by default (except where RIT or SPLIT mode is selected).

However, if you want to change the approach, do the following in uBITX Manager:

– Enable Adjust CW Frequency

– Shift Display Frequency on CWL, CWU Mode

If you select this function, the LCD will show the frequency at which the radio is being transmitted (the offset you prefer is added or subtracted to the actual RX frequency reflecting the CW-L or CW-U mode selected).   This may be just the thing you were looking for!


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.


Michael VE3WMB figured after playing around with the KD8CEC firmware for a while that he  would prefer to have the Main VFO frequency and Mode displayed in the top line, instead of the bottom line of the display and the secondary info (VFO B etc) on the bottom line of his display.

Under ‘User Interface’ of the uBitx Memory Manager application (scroll way down), checking the ‘1/2 Line Toggle’ works to swap the first and 2nd lines on the display.  No coding is required to achieve this.


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!


Using the CW keyer as a morse practice oscillator

A member of the BITX20 list asks, “How can I use the keyer in my µBITX for CW exercises with a paddle?

The answers include:

  1.  Remove the power to the finals (this is the centre pin of the power connector)
  2. Use the KD8CEC software, which has a menu setting to turn off TX
  3. Modify the supplied manufacturer’s software to disable  TX


Getting the VFO in the band when turning on the uBITx

With the manufacturer’s firmware that the uBITX ships with, you need to switch from VFO A to B in order to save the current frequency in EEPROM memory so that next time you power up it will use that last saved value. The manufacturer’s software only saves things if there is a specific event requiring something to be saved (such as changing VFOs).


Variable IF bandwidth from W1EAT

Tom W1EAT provides a  schematic for his mod of a variable IF bandwidth circuit for the µBITx.  The RX and TX voltages are about 12V,  so he used a resistor network to keep the applied voltage to about 1 to 9V because that is the usable range for the varicap diodes he uses.  As the voltage on the caps is reduced the higher audio frequencies are reduced until the bandwidth is probably 100Hz or so at 1 volt. The filter centre frequency is very low, 200 Hz or so with Tom’s BFO setting.

The BB112 has about 500pf capacity at 1 volt applied.

The 4.7K resistors that feed the voltage to the VVC diodes could be 10 or 20 K, or what have you, as there is very little current needed.


Fake PA FETs

Watch out for fake RD16HHF1 devices.   Buying on Alibaba and Ebay is a risk some are willing to take, but there are plenty of fake devices for sale through these channels.