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/vqd4kqa4w2keeqr/AAB4Oo0WNCqPWZMIMh0jt-3Ta?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.
Hello Duwayne, ive been following your build Any location on where you posted your sketch? Ive put together a promini,encoder,si5351 ad8307 and working sketch but would like to try adding a display and sweep function like you have here, Great work, cant wait for the article in QRP :)
ReplyDeletemike kd7ura
Hello DuWayne,
ReplyDeleteCongratulations on an excellent project.
I just had to make one,
My version was built on a single sided pcb, although I did use surface mount components on the copper side, around the ad8307 and I also screened the ad8307, and as yet I have not found a case for it.
While all the functions appear to be working I was wondering if you have a test method or calibration type check? My ad8307 came from china but I don't think it is a fake!
Best regards............Peter GW4ZUA
.
ReplyDeleteI used a power reference based on one from W!GHZ more information in a previous post http://kv4qb.blogspot.com/2015/10/20-mhz-power-reference-calibrating.html
After it was finished I measured the output with a scope and used a table of dBm to voltage conversion to get a more accurate reading, it was within 1.5 dBM http://ifmaxp1.ifm.uni-hamburg.de/DBM.shtml
If you do not have cal signal measure the output of the DDS connected to the log amp and use the table to get a dBM reading you can put in the sketch to calibrate.
Hi DuWanye,
DeleteThanks for the info, will give it a try.
Best regards............Peter GW4ZUA
Hi Duwayne...
ReplyDeleteDo you have a BOM for this by any chance?
I could order by value, but I don't have enough SMD experience to be sure I got the right packages.
/ Gerry
They are all 1206 size. Or you could use 0.1" leaded components with the leads cut very short and bent over.
DeleteGreat, thanks. I'll let you know how the build goes.
Delete73
Gerry
FYI, I DFRobot will do a run of 10x 10x10 boards for < $25
ReplyDeleteGood quality too, or so I have heard. I will report back when they arrive... could be some time.
/ Gerry
Hi DuWayne:
ReplyDeleteI have my snajr up and running, are there simple tests to make the dds and detector circuit is working. I hooked my dummy load to rlb but showing only vertical lines after the sweep.
Thanks and 73 Ross K7RSB
If you have a scope check that you have output across the whole sweep range. With the input open you should have a baseline around -70 db. With a cable from the output to input a sweep should give a straight line around -5 db. Use a 10-20 db pi attenuator in line to check the response of the detector. If that works check the RLB.
Delete