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.

10 comments:

  1. 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 :)
    mike kd7ura

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  2. Hello DuWayne,
    Congratulations 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

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  3. .
    I 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.

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    Replies
    1. Hi DuWanye,
      Thanks for the info, will give it a try.
      Best regards............Peter GW4ZUA

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  4. Hi Duwayne...
    Do 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

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    Replies
    1. They are all 1206 size. Or you could use 0.1" leaded components with the leads cut very short and bent over.

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    2. Great, thanks. I'll let you know how the build goes.
      73
      Gerry

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  5. FYI, I DFRobot will do a run of 10x 10x10 boards for < $25
    Good quality too, or so I have heard. I will report back when they arrive... could be some time.
    / Gerry

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  6. Hi DuWayne:
    I 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

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    Replies
    1. 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.

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