uBitx updates and Build guide

Sidetone issues:
 
Sidetone ‘vanishes’ after a start blip. That’s because the LM386 was being pushed to the rail by the 2.5v DC on the input.
 
Replace the R253 (a resistor) with a 0.1uf capacitor  
 
Replacing the final resistor(R253) in the low pass filter with a 0.1uf capacitor fixes the problem. 
 

TX and RX LED connection

If you bought the case kit from https://amateurradiokits.in/ then use the power connector that came with the board and 3 of the wire connectors that form the connections for the ribbon cables.. 

I managed to sort the twin paddle out, the resistors are included in the kit that comes with the board.. you need to cut a track add the resistors as shown. 

ΜBITX TUNEUP

The µBITX comes pre-aligned. You should do this only if you really think it is out of alignment.

There are three things to be tuned up.

1. PA BIAS

  • Switch off the rig
  • Locate the two PA bias presets (the blue square ones)
  • Set both the presets  to fully clockwise position, gently.
  • Attach a dummy load or a low SWR antenna and switch the rig on
  • Attach a current meter to the power supply so can monitor the current draw
  • Switch on
  • Press the PTT without speaking ( no modulation)
  • The current draw should be between 470 mA and 500 mA
  • Slowly increase one of the two presets until the current increases to by 100 ma
  • Do the same for the other preset (the total current should have increased by 200 ma now)
  • Now, blow a loud HALLLOWWW into the mic.

Does the current flick up?  You’re done with PA Bias

2. Aligning the master clock

All the frequencies of the µBITX are derived by multiplying/dividing to the required frequency from a single 25 MHz crystal. This crystal is rarely at exactly 25 MHz. We have to calibrate this clock to the exact frequency. Here is how it is done

  • Click on the encoder button to display the menu, rotate it to the “Setup On?” and click on to confirm it. This enables the setup options.
  • Tune to an AM broadcast signal with known frequency.
  • Set the dial of the µBITX to read the exact given carrier frequency of the station. If your calibration is out, this will NOT be zero-beat.
  • Click on the encoder button again to display menu and this time it will show up a new option ‘Set Calibration?’. Click to enter this option
  • Now zero-beat to this signal (the frequency display of µBITX will remain the same)
  • Press PTT to save the calibration.

3. Setting the BFO

  • Click on the encoder button to display the menu, rotate it to the “Setup On?” and click on to confirm it
  • Tune to an clean and preferably weak SSB signal to its loudest (not the clearest)
  • Click on the encoder button again to display menu and choose  Theoption ‘Set the BFO’. Click to enter this option
  • Now tune with the encoder for the best sounding audio
  • Press PTT to save the calibration.