Month: September 2019

Jonathan Kayne, KM4CFT, who is studying at Virginia Tech in the USA asks on the IO Groups BITX20 list whether it is possible to do a full assembly of the uBITX.   That is, he wants to start with a bare PCB and hand solder on the SMD components. He plans to use it in a school project.

He received several replies to his query.    Jerry KE7ER suggests:

Be aware it might not be as trivial as it looks.

The transformers are described here:
http://www.hfsignals.com/index.php/ubitx-circuit-description/

Search for “Coil Details”.

The KiCad files are not available, that was some sort of requirement
when they set up HFSignals to build this stuff. Perhaps to get a business loan they had to keep some part of the design private. The remainder of the design is open source, and building from scratch is encouraged. The uBitx is a two layer board, the bottom side is mostly ground plane. Perhaps just build “ugly style” or “Manhatten style” on copper clad circuit board, that way you have a solid ground plane under the entire design, which is highly recommended.

All quartz crystals in that IF filter should be matched by hand to within 100hz or so, that means building a crystal oscillator and having some way to accurately measure frequency. If your quartz crystals have different characteristics than what hfsignals uses, you will need some way to determine the passband of the IF filter and adjust the filter shape as described in Experimental Methods in RF Design (and/or search for Dishal on the web).

You will need some way to sniff and measure RF, an Antuino would be ideal, though you might get by with a diode RF probe and a Harbor Freight DVM. A good scope would be nice, perhaps 50mhz or more of bandwidth. The nanoVNA would be worth looking into, shows complex of 1 and 2 port networks, and thus is an education in itself.

If you are serious about studying “RF and Microwave”, all of the above is worth the investment.

And lastly, maybe you could consider getting a working uBITx from HF Signals, simply so you can  know for sure what the signals levels really should be when yours doesn’t work.  Many have built radios like the uBitx from scratch, but few find it easy.

Ashhar Farhan VU2ESE, the designer of the µBITx has indicated he can arrange for a blank PCB.   He notes, however, that there is very little education in it!   To build an actual ubitx all by yourself would be a better learning experience.

Although the µBITx is a double conversion design, it is actually quite easy to build, stage-wise.  Ashhar suggests building the IF amplifiers first.  You have to build six of these. After getting one going, the rest can be duplicated.  He suggests that each is built on a separate 2″x2″ copper board.

After the IF modules have been built, you can hook up a raduino from the Si5351 board from qrp-labs and an antuino.   Using the antuino as a signal generator, you can test and align the 45 Mhz filter and the LPF.  At that point, you are done with the RF parts and you can choose to go with any audio amplification system.

Ashhar encourages experimenters to build their µBITx one stage at a time, then test, measure and move on.    He suggests it is a great education!!

Reference