Digital interface kit for your uBITx

David N8DAH is now producing a very handy digital interface kit.  This is a Gordon Gibby KX4Z design, and it features:

  • On board 5v regulator that you can power from 12-13.8v or you can leave it off for direct 5v input.
  • Built in VOX PTT via reed relay
  • Input and Output gain control
  • Audio Isolation transformers 600:600ohm

The kits are available for:

US$15 unassembled or US$20 assembled


Full SDR receive with G4HUP buffer amp

SM0JZT has installed a  G4HUP buffer amplifier in his µBITx and uses an RTL-SDR dongle externally.  This is an alternative to the approach used by KD8CEC to add an RTL-SDR that gives much wider bandwidth (i.e. the bandwidth is not limited by the 45MHz filter).   The G4HUP buffer amplifier can be purchased here in either fully built-up form or in kit form.  Order the 50MHz unit is what you need (it has an LPF above 50MHz and requires no modifications to work on 45MHz).

This gives you the best of worlds – a low-cost transmitter and an equally low-cost SDR receiver.   Thanks to SM6MOJ for bringing this to our attention.


A 3.5″ screen for digital modes/ rig control on the front panel

Vince, N2AIE,  worked Tom VE3THR and Bill NG1P tonight on 7.277 out of his QTH in Cedar Rapids IA.  These were his first uBitx contacts with other uBitx and bitx40 rigs.

Vince has loaded (after some angst) the KD8CEC firmware, and has the rig interfaced with Ham Radio Deluxe (in both directions).  His rig also has a 3.5in touchscreen Raspberry pi for digital modes built in on the right hand side of the front panel as illustrated above.

Take a look at the rear panel of his rather attractive build:

An independent audio output for your computer


Walter W9KJO in writing to the list says,

” The yellow wire on the volume control does not have enough audio for my Signal Link to work with.  I have to reconnect to the 3.5mm Audio Out jack and turn the volume up about half way.  which is too loud for my headphones so I need to install a second 3.5mm for my Head Phones.  

“I would be much better if I could find a way to get enough audio separate from the actual audio out to the 3.5mm jack.”

Clark Martin, KK6ISP replies “You could use the second audio amp in U1.  The TDA2822 is a dual amplifier.”   He provides the following guide [with some additions from the editor for the sake of clarity].

Modifications to the µBITx to add a second audio channel for computer use 

  • Remove R75
  • Connect U1 pin 6 to VOL-H.  This will give you an auxiliary sound output that is independent of the volume control.
  • Connect the + terminal of a 470 µF, 16V electrolytic capacitor to U1 pin 3.
  • Connect the – terminal of the above cap to your auxiliary out mini jack.
  • Earth the auxillary out mini jack sleeve connection.
Additional Notes
  1. The 470 µF could very likely be much smaller, depending on the input impedance of your Signal Link.   Experiment, it won’t hurt.
  2. You may also want to add a resistor divider between the cap and jack to reduce the signal strength, depending on how much your Signal Link can tolerate.
  3. Considering the problem others are having with the TDA2822 you probably should add a resistor in series with the cap, unless you implement the resistor voltage divider, that will provide the same protection.
  4. Rather than use a voltage divider on the output of your second audio amp, you may want to incorporate a trimmer potentiometer between VOL -H and pin 6 of U1 similar to the primary volume control to set the auxillary audio output level.