Saturday, May 30, 2015

SNA Jr Software Update

When I first did the SNA Jr, I used my existing Antenna Analyzer software.  After playing with the Chinese SNA, I decided to do a rewrite of the  SNA Jr software to incorporate some of its features.  The major change was to add a settings screen, where I can set the start, stop frequencies, step size, and change modes. Since I added this I removed the PC interface.
The original sweep mode gave a relative reading, showing the  difference between the output of the SNA and the input from the device under test.  This has the advantage of directly showing the gain or loss of the DUT.

  I decided to add an additional sweep mode which normalized the  data before it is displayed, this  makes it easier to measure filter bandwidth.


 One thing I liked about the  Chinese SNA software was the VFO  (signal generator) mode with its RF voltmeter.  I added a similar mode to the SNA Jr with the voltmeter shown as both a bar  and numerical values.  Voltmeter values are still relative to the output of the DDS and shown as a db value and percentage of full scale.

Navigation is the same as in earlier the earlier version.  a long press switches between display and settings screen.  When on sweep screen, a short press starts a new sweep, holding the button while in a sweep goes to a screen to adjust levels.  Using the encoder scrolls through the sweep.
In settings mode a short press moves from one setting action to another, rotating the encoder changes selected setting. In VFO mode the rotary encoder changes the frequency by the step size.  A short press on the button toggles through different step sizes.

In the process of re-doing the circuit board layout to add a MMIC amplifier and attenuator to boost output and reduce loading by the DUT.  Also shifting some parts around to give a little more room so I can go to a slightly larger 160x128 display instead of the 128x128 I am presently using.
I will post the software and board layout when finished.  If anyone is working on building one, drop me a e-mail at and I can send you the software update.



After I got the hardware working with the pickup coil to use the SNA Jr. as a Dip Meter, I decided to add a DIP function to the software.  It does a sweep from 1 Mhz. to 50 Mhz. with 50 KHz steps, and looks for the deepest dip in the signal from the RLB.  After that sweep it sets the  range  to 1 MHz.  below and above the dip frequency and then  does a normalized sweep of that frequency range.  Much faster than sweeping through in several ranges.

After the last local QRP club meeting I was asked about the possibility of making kits available.  Still trying to decide if I want to go this route, or just make the design for boards and software available.  If anyone would be interested in a kit of this project drop me a e-mail at   Depending on the response I will decide which way I will go.

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