It is a while since uBITx.net featured a story on the BITx40.
Jerry KE7ER posted the following on the BITx20 IOGroups list:
“Most traffic in the forum is now all about the uBitx, a very capable rig for all of HF. Those put off by the need for mods to reduce harmonics and spurs on the uBitx should consider the simpler BITx40.”
http://www.hfsignals.com/index.php/bitx40/
Usable out of the box, only issue is that the stock firmware shifts around occasionally by 50 Hz due to noise when reading the tuning pot
with the Nano’s Analogue to Digital Convertor.
Jerry recommends Allard’s basic BITx40 firmware, requires no mods, fixes the operating frequency drift issue, adds a number of other new features. Some minor hardware mods are optional, adding the Function switch is a good idea.
https://github.com/amunters/bitx40
If so inclined, Allard’s bitx40_raduino_2 firmware adds even more features, though does require some minor mods:
https://github.com/amunters/bitx40-raduino-v2
Jerry notes that the Bitx40 is a very good deal at US$59. Being a single band 40m rig it does not have the complications that come from the wide band approach of the µBitx.
Bruce KC1FSZ is also a fan of the BITX40/20 architecture and has had good luck on other bands. One thing he did was to create a “mainframe” of the core of the design (see the manhattan breadboard style construction above) that starts right before the first mixer and ends right after the product detector/balanced modulator.
In his experimentation it seems like 90% of the modification are happening in the “peripherals” around the core (different LC filters, different PAs, different bands, different audio/mic configurations, different software, different enclosures, etc.) so I am able to cover more ground without needing to re-build the inside of the inside every time.
Bruce’s core uses two SI5351 ports so the BFO is tunable just like the VFO making it easy to fool around with different IFs, filter widths, etc. He also based the chain on the W7ZOI TIA amp which seems to improve performance a lot. There is a bit of the uBITX design incorporated in his bottom up construction.
The crystal filter is on a daughter card for easy swapping in and out . He is using ADE-1 mixers on both sides, which are easily and cheaply obtained on eBay, and adjustable gain VFO/BFO buffers (a la N6QW LBS design). The core is 100% symmetric so it’s quick to build and test.
MVS Sarma notes that “try using the 3 transistor bi-directional amp version and see the performance difference. A friend has indicated that the noise level comes down. You could even try with single dual gate MOSFET in each direction.”