Monday, October 31, 2016

BITX 40 v 3

I have been gone for a while visiting family, and have not had a chance to work on the projects I have on the bench.  One of these is a SMD version of the BITX 40, that was only available in India.  Just before I left, I saw that a newer SMD version was available for sale world wide.  And, at only $45.00 including shipping I decided to order one.  A couple of days after I returned home, I received a little box from India.  Inside was a very nice assembled SMD BITX board, and a bag of components needed to build a working transceiver.  Since the local QRP club was going to have a table at a hamfest next week, I decided to quickly build this up for something to display.
I want to make a few minor changes to the kit, first I wanted to use a 10 turn pot instead of the one included in the kit.  Along with that I will add one of the re-packaged DL4YHF counters I designed a couple years ago. I also will use an external hand microphone with PTT instead of the electroet mic. that came with the kit. 

 Next was to come with a case to put it in.  This is exactly what I bought the 3D printer for.  I printed some 6" corner pieces I had designed right after I got the printer, and cut up some double sided circuit board material to use for the sides of the case. I have switched to using .032" PCB material for chassis panels. It is very easy to cut accurate size pieces with a simple paper cutter. The back panel is very simple just two mounting holes for the power and RF connector, and 4 screw holes for mounting the panel.

The front was a little more difficult.  I needed mounting holes for the tuning pot, volume control,a separate power switch, along with a hole for the display. I also decided to add a grill opening for a small speaker to mount behind the front panel.  I went with a panel .2" thick to give room to build in a bezel for the display, and allow enough depth to add a recess to hold the 7 segment display for the counter.
After a couple hours to lay out the design and a few more to do the printing I came up with a very nice looking case for the project. I cleaned up the printed parts, assembled the top and bottom of the case, and gave everything a coat of paint.

 Now to put everything together tomorrow, and see how it works.

Friday, October 7, 2016

Another SNA Jr. lives

I have been exchanging  e-mail  with Caglar TA2UH , concerning compile problems with the SNA Jr. he is building.  Only problem seems to have been the version of  the 'rotary' library he had been using.  After sending him the correct one, he now has his Junior working. .  It still needs to be put in a box and some accessories built, but from the picture he sent me it looks like everything else should not be a problem.

I just copied the correct version of library to the SNA Jr version II dropbox folder to help eliminate this problem for builders. 

Just got some pictures of  Caglar's finished SNA Jr with some accessories. Looks great, a lot of work with some hand tools to get it fit into a cast aluminum box.  

 And another of it in use testing a crystal filter

 ANOTHER ONE   10/14/2016

Just received an e-mail from Vincenzo IZ5GVP with some pictures of his version of the SNA Jr.  He also included an Arduino sketch with some of the additions he has made to the software.  I took a quick glance at it, and it looks very nice.  I will take a longer look  (with the help of Google Translate) and  see what I want to add to my version of the sketch.

When I did the latest version of software, I was in a hurry to get everything ready for FDIM.  I did not do much in the way of calibration, Vincenzo's sketch has some cal routines that I will defiantly have to look at.

And another one from John VK5COR, he made his own 2 layer board.  He said it worked but didn't look very nice. then he had a couple boards made.  Said they look a whole lot nicer.  He is now working on a box to put it in. 

It is very gratifying to receive e-mails with pictures of other peoples build of some of my projects.  Sometimes when you write a blog, you wonder if you are just wasting your time.  When you get pictures of other people building your projects, you know that what you have written is of interest to more than just yourself.  So please if you have built any of my projects please send a picture and I will put them in a Dropbox folder for all to see.


Thursday, October 6, 2016

8307 power meter repackage

I was adjusting the gain on several broadband amplifier stages using a noise generator and my AD8307 power meter.  It worked well, but was a little inconvenient without a small test probe.  A couple months ago some one had brought a RF probe from QRP Guys for show and tell at our local QRP club meeting.  I liked the format, but I preferred the direct reading in dBm. that I have with my existing meter.  I guess it was time to see about doing a repackage.
It was very easy to move the components in the layout, and change from an Arduino Nano to a Pro-mini. Switching to the Pro Mini allowed me to stack the display directly over the Arduino.  This reduced the width of the board, and gave me a nice probe like form factor. I etched up a board and assembled the new format meter.  I had one small error in the board, but a simple jumper took care of that. After changing some pin assignments in the sketch, I had everything up and running. Now it was time to see about packaging it.  
I have been playing with the CAD software I use with the 3D printer.  I tried several ways to make a housing with a top and bottom piece, but couldn't get one to print that held together tightly. 
Probe Cross Section
I had made a set of corner pieces for a cabinet that had in a built in PCB holder that had worked well.  So I did a design that was basically a rectangular tube with built in slots to hold the PCB. display board and centering for the display itself. It also kept the 9 volt battery from moving around.  I printed a long tube with this cross section, and checked that everything would slide in easily.  It looked OK, but I wanted it to look more like a probe. With a little cutting and slicing of the design I had a nice looking probe housing with cutouts for the display and on/off switch. Simple pieces closed up the open end and provided a removable cover for the 9V battery compartment.

I kept the SMA connector for the input to the meter.  That allows me to use a cable to check output levels of modules with connectors, or install a probe tip for in-circuit measurements.  One thing I decided to add to the software was  to display the difference between the last peak and current reading.  This allows you to get the stage output level, then go back and take the stage input reading.  The displayed difference should be the stage gain/loss in dB.  I took some readings across several known value  in line attenuators,  and found it very easy to measure stage gain/loss.