uBitx v5 Changes
Theses are the changes implemented in v5 of the uBitx to address spurs and harmonics.
- Q10,11,12 and Q20,21,22 changed to BFR93w (or BFR106)
- bfr93w are used in the front end instead of 2n3904. We needed more gain at 45 mhz and the 2n3094s were struggling at 10db gain. This change improves the overall sensitivity
- Change the resistors R26 and R46 to 220 ohms (from 470 ohms).
- This increases the darlington pair's standing current and decreases the Harmonic distortions.
- 45 MHZ LPF ( Consists of an L-C-L of 300nh, 47pf, 300nh. ) in place of R27. See here
- LM386 is back.
- All hail the cross-over distortion sickness!
- The IF is now 11.059 MHz
- These crystals are easily available, with 68 pf, they give a pretty good 2.7 KHz band pass. As their frequency is away from any spur of 16 MHz and 25 MHz (the two crystal oscillators on the Raduino) hence, no spurs!
- Upgrading existing boards ?
- Test new 11.0592 MHz XTALs in an oscillator and sort such that each crystals are within 100 hz of each other.
- Replace C217, C218, C219, C220, C221 with 68 pf
- Change IF in Firmware and re-calibrate. More details to come...
- The relay switching scheme is different.
- The 30 MHz LPF is now always on, the individual LPFs for lower bands are switched in or bypassed (by default). It is easily understood in the circuit diagram.
- The CW wave-shaper uses 1 uf capacitor in place of 0.1u (C1 ?)
- this reduces the key-clicks
Spectrum scans on https://groups.io/g/BITX20/album?id=84174.
Latest Code and diagrams for v5 here. The new firmware breaks backward compatibility!
Thread: uBitx v5 is in production