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.

Saturday, June 18, 2016

Back to the Spectrum Analyzer project

Now that FDIM is over and finished with the SWR - Power Meter for the QRP club, it is time to get back to some of my other projects.  Top of the list is the Spectrum Analyzer.  Looking at the modules I had finished, and some of the things learned when I built the SNA Jr II, I decided to make some major changes in the overall design.  The first change will be to the interface board.  The new board will be similar to the SNA Jr. II,  I am going to include the AD8307 circuitry on this board, and have provisions for a si5351 or si570 on the same board.  For the first try, I will be using the si5351 board from QRP-labs.  This has a very close pin-out to the Ad9850 modules used in the SNA Jr.  I plan on using machined pin header stock to create a socket for the QRP-labs board.  If I later want to try a si570, I will build a small breakout board with the same pin-out.  Then it is just a matter of plugging each board in to see if there is any noticeable difference in the results I get.  The si5351 would have an advantage, in that I could program one of the other clock outputs to use as a tracking generator.
The other main change was in what I was going to use as a user interface device to control the operation.  On the SNA Jr and other projects I used a rotary encoder with a built in push-button.  This worked quite well, but the software got to be fairly complicated as more functionality was added to the software.  I thought about push-buttons, but they would take up a lot of panel space.  And from using several other devices with push-buttons I really didn't think that was what I wanted.  I had a couple of the small joy stick controller boards that I picked up for something else, and thought I would give them a try.  I wired one up on a breadboard, and tried several different methods until I came up with one I liked.  A ReadJoystick function reads the Horizontal and Vertical axis position, and if it is more than 20% from center updates a global variable for that axis to either + or - 1 depending on direction.  This joystick also has a push-button, so I detect  either a short or long push, and update another  variable with that value. To make processing these variables a little easier, I only allow one to be changed at a time. If any of these occurs a global flag is  set.  This global flag allows the flag to be reset in the program to speed up processing by bypassing further testing in that pass through the loop. 

I did a  quick board layout  and etched a board to test the functionality.   Since all the pins used by the display except reset are through the end connector on the Mega board, I have all the other pins available.  This makes the board a lot easier, because I can just use a tall stacking connector and not have to do anything on the interface board for the display except bring out a couple of pins for the reset line. I also included several places on the board for push buttons that I might use for more advanced features later on.  And also brought out a couple  sets of I/O pins for control of the RF boards.

I took some of the code from the SNA Jr. and modified it for use with the new board, display and Joystick.
It was quite a bit simpler, and worked very well.  I think the Joystick will work nicely in the Spectrum Analyzer.  I really like the larger, higher resolution displayWith it having a parallel interface instead of SPI the response is nearly as fast as the small display in the SNA Jr.  It has already got me thinking about a SNA Jr version III.

 With the power detector and clock generator on the same board, I can modify more of the code from the SNA Jr. and have a stand alone version of the Sweeperino for testing some of the RF filters in the Spectrum Analyzer.  Then after I finish the RF circuitry, I can just connect it to the interface board and change the software to make it a Spectrum Analyzer.

"This is such a great time to be in the hobby"

 After the two days at FDIM, I went and spent a couple weeks helping my daughter with a few things around her house.
I did a little computer work on some of the projects I had started, but mostly followed some of the blogs I keep track of.  One of them is by Pete N6QW.  After a couple of e-mail exchanges concerning some of his new projects, he ended one with "This is such a great time to be in the hobby".  I couldn't agree with him more. 

When I started in electronics in the mid 1960's , an instrument with the capabilities of the SNA Jr. would have cost many thousands of dollar and fit in a 19" rack.  Now it is a hand held unit that cost less than $30 to build.  This is mostly due to the fantastic advancement in micro-electronics, especially the new micro-controller chips that are available.  

The first job I had after I got out of the ARMY in the late 1970's was as an engineering technician in a very small company.  One of the  projects I worked on, used what I might consider an early predecessor of the Arduino type controller.  It used a single board computer, with a 4 Mhz Z80 processor, 4K RAM, room for 24K e-prom, and 16 IO pins.  It was about 1 foot square, cost  $250, and you needed a few hundred dollars worth of software to develop anything for it.  Now it is a $3 Arduino Pro-Mini about the size of a large postage stamp, and the software IDE is free.  Along with the Arduino or other micro-controller board, you have all the  peripherals such as LCD or TFT displays , DDS and PLL modules, and of course the many ICs availble.   Some times the hardest part of the design is to decide which of the many options you want to use.
The Internet has made all these parts readily available through the on-line catalogs of major suppliers such as Mouser, and DigiKey.  Other suppliers such as AliExpress and Bangood that offer a large selection of electronics components.  And don't forget eBay where you can get almost anything from around the world.  The Internet has also allowed small companies such as Adafruit, and SparkFun to build a successful business supplying specialty products to an ever growing MAKER market.  Related to Ham Radio, you have suppliers such as Kits and Parts, QRP-labs that offer products that are more directly related to RF projects.  

The Internet also gives you access to information on almost anything you might want.  From product data sheets to service manuals, and individual blogs,  almost anything is available.   Just add DIY to almost any search and you will be amazed with what is available. Want to build your own electron microscope, search "diy electron microscope".  Over 200K hits to choose from.  Of course only a very few might be useful, but there is some great information on what other people have built.

With the smaller solid state devices, construction methods have changed.  You no longer need a machine shop to build something, but it is really nice to have one.  Using methods such as "Manhattan ", "Ugly",or prototype circuit boards, some truly wonderful projects have been built.  My preferred method is to make a Printed Circuit Board.  Layout is very fast using one of the free or evaluation PCB software packages such as KiCad, Eagle, ExpressPCB.  Then using toner transfer, I can etch a nearly professional looking board in a few minutes. A little bit longer, and I can add a usable solder-mask. You will not have some of the nice features such as plated through holes for double sided boards, but with careful layout you can minimize these problems.  Some people have commented that this takes too long, compared to "Ugly" .  But, I have found that it is much easier to trace for errors on a PCB before building than to check something done "Ugly" after it is built.  
If you don't want to etch the board yourself, you can send the design off to one of the many PCB houses to have them made.  One of my favorites is OSHpark.  They take my Eagle file directly, and for $5 a square inch including shipping, I get three solder-masked double sided boards with plated through holes in about a week.  For larger quantities or size boards, I tried one of  Chinese board houses.  For less than $35 including shipping, I got 10  double sided solder-masked boards with plated through holes, around 10cm. by 10cm. in about two weeks. 
One comment I get is that it is getting harder to find through hole leaded components.  I have found that using surface mount devices SMD it is much easier and faster to build most of my projects.   I don't have to drill nearly as many holes in the boards I etch myself. If you use the larger size SMD components 1206 or 805 placement is quite easy.  If I don't have a component in SMD I can just layout a couple large pads, and solder on the leaded component after bending the leads.  If you don't want to go to SMD , you can check out the "Muppet" method championed by K7QO.  Using solder paste and a hot air gun, construction is much faster than having to stuff and then flip the board over to solder through hole components. 
All in all I will have to agree with Pete,"This is such a great time to be in the hobby".  I might even say that this is the "greatest" time to be in the hobby for the home builder.



Now that I am back home, it is time to think about some of the other projects I had started, and get busy working on them.

Monday, June 6, 2016

SNA Jr. II update UPDATED 8/29/16

UPDATED 8/29/16
To make it easier for those that want to build their own SNA Jr Ver. II, I have uploaded the Eagle files to OSHPark.com.  Boards can be ordered from them if desired.  If a  couple people want to get together and build some, cost is about $49 including postage for 3 boards.  They can be found under the shared projects as

SNA JR DDS large format ad8307.brd



UPDATED 7/25/16

The SNA JR II took the best in best in show in the home brew contest at FDIM, and because of  many suggestions I wrote an article for QRP Quarterly.  Just got my July issue and found the article has been published.  I put together a Dropbox folder with the documentation needed to build your own. The  Eagle cad files for the board and parts layouts are included.  It also has the latest Arduino sketch and a number of pictures of the construction.  I have also included a document covering the basic operation of the device.
They are available at
https://www.dropbox.com/sh/axyu01rttytlubg/AAB8UrBlqCEERAR1HFrHxpv1a?dl=0


Just before I went to FDIM I was able to get the SWR function working on the SNA Jr.  With nothing connected to the input to the Return Loss Bridge, I did a sweep and measured the average return loss and stored in the sketch.  I use this value when converting from return loss to VSWR.  I used the SWEEP.R routines to do a sweep of the desired frequency range.  After the data is acquired I  normalize the data using the previously found average return loss.  Using the integer value of the return loss, I use a simple look-up table to find the VSWR.   The display routine now uses the VSWR value and plots  the waveform.  Since I only use integer values for return loss, the plotted wave is a little rough, but more than adequate for normal usage.

Here is a plot of my 80-40 meter end loaded dipole. Sweep range is from 3 to 9 Mhz, so each horizontal division is 1 MHz, and vertical divisions are limited to a SWR of 4:1.   You can see the narrow SWR dip around 3.950 MHz and the low SWR reading of 1.29 : 1 at 7.2 MHz.