uBITx build from scratch

Anthony VU3JVX has shared details of his ubitx built from scratch.  He has dedicated his description to Ashhar Farhan as he says, “Farhan has always motivated me to homebrew stuff.”

Anthony gained his license on March 2017. Passing the exam, and getting on HF bands are still two different things. He began by working on the local VHF repeater with a cheap Chinese Baofeng radio –  probably the most economical way to start out as an amateur radio operator.  However, he knew that he was missing out on something since I was unable to operate on the HF bands.

Around the time he got his licence, Anthony noticed that the Bitx40 was available as kit from HF Signals. That’s how he made his first HF rig.  In joining the BITX20 forum he learned a lot from all the great people caring and sharing information.

He  was already thinking of building BITx40 for another band (because these designs are easily modified) and then the µBITx design was announced.  This changed everything.

He studied the µBITx circuit and begun collecting all the required components.  He even ordered the indicated toroids from the W8DIZ website.

Anthony found it difficult finding sufficient time to put things together on the bench.  By profession, he is a computer network & security engineer. However, he lost his job in July. Not sure what to do next, his XYL suggested that he should focus on something he had always wanted to do, but had never had sufficient time to do.  That’s how he started on the journey of building the µBITx from scratch.

He started building the receiver segment first. He had his challenges during this time and at one point thought he had made a bad choice in deciding to build the rig the hard way.   He wondered if he should have tried the bitx40 circuit first.

He was almost on the verge of packing up and shelving the project because he couldn’t hear anything from the receiver.   However, h took a break for few days and then started troubleshooting each section of the receiver in sequence.   Finally he found after reading through the BITX20 forum that the Q70 was likely to be defective.  He decided to replace it with an audio type transistor 2SC945.

In this process Anthony read through most of the content of the BITX20 forum!

Anthony had all the version schematics but started out to build the V5 as he wanted to include the best new features.  He kept the build approach modular and laid the modules out almost like the schematic for easy troubleshooting.

The next challenge was trying to be a good student and follow everything as suggested by Farhan.  He made up the 11.059 Mhz crystal filter and after changing the X7 to 11.059 Mhz  he was able to see the radio signal making it through the crystal filter.   Then came the hurdle of fine tuning the USB and LSB and fiddling with the software for the right value.

After the receiver started working he took a break and started enjoying the receiver and checking out all the amateur bands.

He quickly moved on to building the ubitx transmitter.  He was quite confident that he could get the transmitter built by now and thought it should be straight forward.  He was so wrong.  Following all the recommendations on the forum about harmonic issues and how to avoid them, he started building Band Pass Filters. Then he started work on the PA section  He succesfully adjusted the bias current on the IRF510s.   He calls this his “Bell the cat moment”  since he didn’t get to blow either IRF510.  However, the output power on 40 M was barely 2-3 Watts and on higher bands was less than 1 Watt.

He suspected something was wrong with those MOSFETs,  but out of circuit  tests on the MOSFETs suggested they were working normally.  He had some other units from a different source, but these performed exactly the same.

Anthony played around with different PA transformer settings and rechecked and traced the RF signal. Everything looked normal until the IRF510 linear amplifier stage.  The chances of receiving fake IRF510 is generally low, as this is not an expensive RF part like the RD16HHF1.

Anthony happened to have some new RD16HHF1 parts.  He was not very hopeful thinking that they may well prove to be fake since they were purchased online. However he gave these a try.  The pin layout was easy, given the design approach (see the photos).

He was surprised to find he was getting a whopping 10+ Watt output on 40M, 5W on 20, 10W on 17M, 10W on 15M, and 5W on 12M and 10M.  It appears there are a lot of fake IRF510 on the internet!

Now it was time to test the homebrew rig on air.  He checked in that evening to the All India Net and got a 59 report.  The net controller assumed he was using a commercial rig.   Finally,  despite difficult times in his personal life he was able to smile and sleep well that day.

The icing on the cake will come with installing the Nextion 3.5 display.

Does that mean everything was 100% with his home brew ubitx ? No!  He is still trying to figure out how to fix a feedback issue from the speaker during transmit.  He found this seemed to be audio leaking from the emitter of Q6.  He has still not solved the audio leak on TX problem.

Anthony has tried out all the audio circuits used in the µBITx.  He finally settled for the TDA2822 circuit [presumably with the authentic part!].

Anthony is happy to share any information related to his build or software settings or tuning.  He is very familiar with programming in C++.

Reference

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