Tuesday, June 28, 2016

A Surface Mount version of the BITX-40

Because of the availability and price point of the BITX40 board now available through hfsigs.com.  I have decided to stop work on my version , and now work on modifications and upgrade to that board.

I have been happy with the results I have been getting with new version of the Spectrum Analyzer interface board.  Unfortunately now I am waiting on the new si5351 board I want to use.    Looking around for something to do I came across the BITX-40 board by Asher Farhan.  This is a single board version of his BITX design, and is being produced by a collective of local women in their homes to provide a livelihood. 
More information including schematic and a great circuit description is available  at http://www.hfsigs.com/
I had previously started a modular version of the BITX, but this looked like would make a nice small portable transcever.



This board is only available in India, so if I wanted one I would have to build one for myself.  I decided to layout a board using using SMD components.   Although I am using SMD components, I will keep the board size about the same as the original.  Since I will be using a home made  PCB without a solder mask I used 1206 size components and allowed plenty of space around each component.  Without a solder mask it is very easy to have problems with solder bridges with SMD components.  I also made it a double sided board, with the the DC power lines on the bottom of the board.  Unlike the original, I did not include the VFO and BFO circuitry.  I plan on using a si5351 much like the one I built for the Canned Frog. 

Because of the size of the board I could not use the free version of EAGLE that I have been using. There are several other free PCB design software packages around, but I had some experience using ExpressPCB.  There is not a large  component library as available for EAGLE, but it is fairly easy to add custom components to the ExpressPCB library.  The other issue with ExpressPCB is that it is designed to be used with the ExpressPCB board service, so there is no provision for generating  Gerber files if you want to use a different board service.  One of the other PCB software packages I had tried was Copper Connection.  It was fairly easy to use, but I preferred ExpressPCB.  One of the things Copper Connection can do is read ExpressPCB files and then generate Gerber files.  It also has a very easy way to print the bottom and mirrored top copper layer for use with toner transfer at one time.  So I will use ExpressPCB to layout the board, and export that to Copper Connection to print the toner transfer images.
After I finished the layout, I tried to make a board.  I have had very good luck using the Cold Toner Transfer method, But because of the board size, the clamping fixture use would not cover the whole board, and I ended up with areas on the board where the toner did not adhere to the copper.  
I tried using the Hot method with my laminator, but could not get the toner to stick to the copper at all.  As a last resort I processed a board with the Cold method solvent, and instead of using the clamping fixture I fed it through the laminator without waiting for it to heat up.  I ran it through a couple more times as it was warming up and when I checked the board and it was nearly perfect. I had to touch up a few pinholes in large copper pours, but all the traces were perfect.  I got the board etched and now to start building the board.

5 comments:

  1. nice board. wish you good success in managing it work.

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  2. I like all your projects DuWayne. I am thinking about using your BITX layout and do it in CirCad. I been using CirCad for some time now, bought a copy of it since I do some free lance layout work for mad money from time to time. You have great Blog. John kg9dk

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    Replies
    1. When I finish building the xcvr and get every thing checked out I will publish the board files so others can build one. So far I have only found one very minor error on the first board, and see a couple of changes I want to make.

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  3. Hi DuWayne:
    I am inrerested building the BIT40 xcvr and was wondering if you have publised the board files yet.
    Thanks Ross K7RSB

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  4. Still building and testing, will post files when finished.
    DuWayne

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