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
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
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.