Wednesday, May 11, 2016

SNA Jr. version II update

Well, after a lot of time working on the top half of the box for the SNA Jr. v.II, I have it finished.  It took quite a bit of time with some small files, but it looks very nice.  The extruded aluminum box is nice and solid, the push button on the rotary encoder has a nice solid feel.  Earlier versions using small tin containers flexed when the button was pushed, and it felt kind of mushy. 

Did some work on the software, and now have most of the basic functionality working with the AD8307 instead of the diode detectors.   With the diode detectors I had range of about 50db, with the AD8307 I have a range of about 10 to -75 dBm.

 Finished making changes to get all functions to use the AD8307 and added a simple Frequency Correction  factor to correct for the ~11dB drop in signal output I saw when sweeping form 1 to 40 MHz.  This large drop is probably because I did not include a buffer amplifier, and just take the output of the DDS module through a 100nF capacitor.  I have not had any problems using the instrument for what I want without an amplifier, so decided not to complicate the design.

I added a Watt Meter function for use with a 40 dB. Tap.  It gives the signal in dBm and auto scales to either  a watt or miliwatt reading .  I also keep a peak power reading for each time RF power is detected.  With no power applied the screen flashes NO POWER and resets peak reading after 2 seconds.
Watt Scale
milli Watt scale

I want to add some calibration routines if I have time.  Also trying to get some preliminary assembly instructions written for the pilot run of the SWR/power meter before the club meeting this Saturday


  1. I really like what you guys are up too. This sort of clever work and exposure.
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  2. Can't wait to see the complete article.
    I appreciate your work.
    De John