When Farhan announced that BITX40 Module boards would no longer be produced, my first thought was that it is, of course, still possible to homebrew a BITX. Anthony VU3JVX proves that in his wonderful description of his uBITX scratch-built homebrew project. Anthony obviously learned a lot -- perhaps the most important lesson for new homebrewers is what Anthony did when he couldn't get the receiver to work: HE TOOK A BREAK and went back after a few days. That is very important.
I also liked very much the fact that Anthony did what Farhan did when the receiver came to life -- he stopped building the transmitter and just listened to the receiver that he had built. FB OM.
And three cheers for Anthony's XYL -- she was very wise to suggest that he take on a project like this when he found himself out of work.
Anthony VU3JVX wrote:
I would like to share my journey of building ubitx from scratch, I would also like to dedicate this to Farhan (hope he will read this sometime) as he has always motivated to homebrew stuff.
I got my license 'VU3JVX' on March 2017. Passing the exam and getting on HF bands is still two different things. Yes, I started to transmit to local VHF repeater with cheap Chinese Bafong radio, I believe the most economical way to start the ham operator experience. However, I knew that I am missing something since I was not able to operate on HF bands.Coincidentally I saw that bitx40 became available as kit from HF Signals during the same time. I was happy to try it and that's how I made my first HF rig. Then I came to know about the BITX20 forum and joined the same, one of the best thing I did after buying bitx40. I have learned a lot from all the great people caring and sharing information. I will try to contribute whatever way possible from my side in coming days.
I was already thinking of building bitx40 for other band (because the way Farhan Sir has drawn the schematic it becomes so tempting for DIY) and then ubitx happened and it changed everything. I started studying the ubitx circuit and collecting all the required components, even ordered the exact toroid from W8DIZ website (during my good days and travel to US) but I was not having enough time to put things together on the bench as I am by profession a computer network & security engineer. I was not sure what to do next, during this time my XYL suggested me that why don't I focus on something which I always wanted to do. And that's how my journey started to build the ubitx from scratch.
Honestly, I was not sure if this was the right time to start this project. So I started to work on building the receiver segment of ubitx only. I had my challenges during this time and at one point I thought I made a wrong choice of building ubitx, instead I should had tried the bitx40 circuit first. I was almost on the verge to pack up and shelf the project because I was not able to hear anything from the receiver itself forget about building the transmitter. Then took a break for few days and then started troubleshooting each segment one by one. Finally I found it after reading through the bitx20 forum that my Q70 to be defective then I also came to know that is it better to replace it with audio type transistor 2sc945.
I believe during this process I have read most of the content on bitx20 forum. Some name which repeatedly comes to my mind are Raj (vu2zap), Allison, Jerry and thanks to all other hams out there. I had all the version schematics but started my work based on V5 and wanted to get the best out of all the version so I kept the build approach modular and laying them almost like the schematic for easy troubleshooting (you can see those pic on my qrz page).
Next challenge was trying to be too good student and follow everything the master said (pun intended). I made a cocktail of 12 Mhz with 11.059 Mhz crystal filter (Farhan Sir I believe the schematic is still showing X7 as 12 Mhz) and after changing the X7 to 11.059 Mhz I was able to see the radio signal making it through the crystal filter, then came the next hurdle of fine tuning the USB and LSB and fiddling with the software for the right value. After the receiver started working I took a break from building the radio and started enjoying the receiver and checking all bands. One evening I narrowly missed Farhan ji on air but anyway I would not have been able to communicate with him since my ubitx transmitter was not ready.
After that day I thought of building the ubitx transmitter soon. I was quiet confident about the transmitter build by this time and thought it should be straight forward. Logically yes it should had been that way but I was so wrong. Following all the recommendation from the forum about harmonic issue and how to avoid them I started building the BPF. Then I started to work on the PA section then came tuning the IRF510 current (I call it "Bell the cat moment") luckily I never blew any IRF510. However, the output watt on 40 M was hardly 2-3 Watts and other higher band less than 1 Watt. I knew something was wrong with those MOSFET but out of circuit the test look normal. I had some other stock from different source even those performed the same. Played around with different PA transformer settings and checking/tracing the RF signal. Everything looked normal till IRF510. Chances of fake IRF510 is less (as debated on the forum) as it is not an expensive RF part like RD16HHF1. Now I was confused, I had some spare new RD16HHF1 which I got online, which I was not very hopeful thinking that it might be fake. I thought of giving it a try (pin layout configuration was easy for me as I have taken the island cutting approach on single side copper board).
Voila ! I got a whopping 10+ Watt 40M, 5W on 20, 10W on 17M, 10W on 15M, 5W on 12M and 10M. Yes there are lot of fake IRF510 out there. Now it was time to test the homebrew rig on air, checked in at evening into All India Net and got 59 report and the net controller thought I am using commercial rig. Finally during these difficult time in my personal life I was able to smile and sleep well that day. The icing on the cake was installing the Nextion 3.5 display (If I remember correctly this is single most expensive component in the radio and thankfully it is optional).
Does that mean everything is 100% with my home brew ubitx ? Nope, I am still trying to figure out the feedback issue from the speaker during transmit. I traced the issue and found the audio leaking from emitter of Q6. I would like to mention that I tried all the audio circuit and finally settle for TDA2822 circuit. However, the issue is still there during transmit so I have made the audio circuit offline during transmit, I know this will impact my CW listening while transmitting when I upgrade my license . I have exhausted all solutions from Bitx20 forum but still no luck. I would be happy is someone can point me to the right direction. I would be also happy to share any information related to my build or the software settings/tuning, yes I like programming especially 'C' so I am comfortable with Arduino programs. I am thinking of building another PA module with IRF510, I personally feel IRF510 (I got the original finally) has made the home brewing so interesting.
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| Anthony VU3JVX |
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