v5 Alive! (plus my advice, and thanks)


Hi everyone.  Kudos to Farhan, HF Signals, Raj, and all the helpful people in this community.  I "finished" my uBitx build this last weekend and made several contacts on CW and SSB with good reports.  I also listened quite a lot to the contest, shortwave, and BCAM.  Receiver sensitivity is very good.  My commercial radio is an old Kenwood TS-830, and I live in a quiet location up the side of a mountain.  I have tuned very weak stations on the KW, and A/B tested with the uBitx.  I have yet to find a signal that I can't hear on the uBitx.  It's a good little radio.  I can't overstate my enjoyment of this build project.  I said "finished" above because there are still a lot of experiments to try with my now fully working radio.

Details:  v5 board, stock display, KD8CEC v1.22.  I first assembled the rig with stock software on an open aluminum chassis to make sure I understood the parts.  I also have a few pieces of test equipment which really helped:  a frequency counter, an oscilloscope, and a software controlled dongle (Analog Discovery 2) that can do FFT (a poor man's spectrum analyzer). 

Issues:  By far my most time consuming activity was reading through this site and various blogs to understand details of the design or program features.  I had the encoder wired up backwards, I had several plug jacks wired wrong.  etc.  Normal assembler errors, but each was another research exploration.

Calibration was challenging for a few reasons.  The calibration procedure for the stock software is fine, but it's different from the procedure for the CEC software so I had to relearn.  I had to figure out the CW Shift programming, to understand the design for sending a CW carrier.  I did finally adopt Ian's mathematical iteration approach using the uBitx manager 1.11 tool, with a spreadsheet and the frequency counter (third calibration procedure learned).  I was able to get the uBitx to within just a few Hz of my counter.  Of course my counter isn't calibrated, and the uBitx probably isn't temperature stable so this was mainly a learning exercise.  I will be checking the calibration regularly though.

BFO setting was another significant challenge.  Mine arrived from HFSIGNALS with a setting of I think 11052.  I could not hear anything because the BFO was putting the signal outside the bandpass of the crystal filter.  I suspect that this is common based on how many people report not hearing anything when they start the rig for the first time.  I ended up near to 11055.5.  Many on this list recommend using FLDIGI or other audio frequency displays to refine the bandpass.  Copying this approach I put my AD2 on the speaker terminals and looked at 0Hz-5000Hz.  Perfect, I could see the bandpass of the crystal filter, I adjusted to get the bottom skirt down around 350Hz.  This is still a work in progress since the same filter is suppressing the carrier on transmit, there is a balance to be struck.  On transmit I was able to put the AD2 on the RF output (using 47dB attenuator tap on dummy load! Don't blow up your test equipment!).  I can look at the difference in the fundamental power on CW, vs keying the mike in SSB with no audio input.  It looks like my carrier is suppressed about 30-35dB.  This seems ok but I can still hear the carrier whine if I tune near it using a nearby receiver.  I am still thinking about the trade off between carrier suppression and good low end audio, I'm sure I will fiddle with the BFO some more.

I probably should have put "loading software" as the first issue, I spend a lot of time figuring out which version is the latest version, for my particular board and my particular display, and getting all the steps squared away.  Once you have it figured out it's just a moment to load, but it took quite a while to get everything organized.

The big question everyone has is what about spurs and harmonics.  Using my AD2 as a spectrum analyzer, my radio looks pretty clean, but I do see the third harmonic.  Using my non-calibrated bench, it looks like my build has the third harmonic down about 38dB.  I played around quite a bit with different bands, adjusting the gain on RV1 down to output of 5, 4, 3 watts.  I tried using CW and also putting a 1000Hz at 50mV signal into the mike circuit.  This testing is not conclusive because it's at the upper limit of my skill and tools ... but I definitely see the third harmonic and it's not below 43dB on my amateur bench.  So I'm going to do more testing ... For the moment I'm not losing sleep over a stray 500mV RF signal.  Most likely I will add an external filter to take it the rest of the way out. 

My advice to a new person who is thinking about building this radio ... it's pretty obvious, but this is not a plug and play building experience.  It's not the linear kit build of the Heathkit days, with check boxes and step by step instructions.  The uBitx is a kit of parts, you have to figure out how to put it together ... and there are a lot of options and choices you have to make.  I did not keep track of how much time I spent on my build, but it wasn't soldering iron time.  By far the time was spent reading through this group, other builders' blog posts, and some basic electrical component theory (how does the click-switch thing on a variable pot actually work?  How does a rotary encoder actually work?).  When I finally figured out how it is supposed to work, soldering up (or loading software) was a small amount of time.  I have built a few things (smaller than this) with step by step linear instructions but I took on the uBitx build as a step-up challenge.  I also mentioned my test equipment, which really makes a difference.  I believe that some really skilled builders get it built using nothing but a soldering iron, but I would say that is an extra level of difficulty!  My advice is don't try to do this kit as your first beginner kit, and also handicap yourself with having no test equipment. 

All this being said, I love this build, it's a great learning experience and I want to thank everyone in this group for such a helpful and friendly community. 


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