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Monday, April 10, 2017

A compact swr analyser and wspr generator using ad8307, atmega328 and dds and a nokia 5110 lcd

Here is a log of my experience in building and boxing a  simple VSWR analyzer. The idea is to make it small, and confined to a box (so that the components are saved from my frequent tinkering and impulses) and to cram maximum things in a small box.

If you want to build immediately, please go to my completed (old) project with source here . This one is still going on and at an extremely slow pace. But I thought of sharing the history of a small project to help out with others who are doing it from scratch. Theses are minor things which many of you already know and can skip this article if you are a regular home-brewer.

A simple swr analyser and wspr signal generator using ad8307, ad9850 and AVR

A short overview of the features
  • Small form factor and use inexpensive and widely available enclosure, modules, parts etc
  • Use a simple LCD (Nokia 5110) to plot the SWR for HF bands and use the DDS as a standalone signal generator, beacon generator, SWR generator and possible keyer for CW
  • Replace the diode + opamp detector in my previous project with a logarithmic detector (ad8307)
  • Make a simple PCB for easy build and some SMD components to save space and better performance
  • Try my homemade PCB for fun (a lot of time used ..)
  • Learn the struggle with eagle and cad software and trouble with encasing a project

Inside peep

Inside view of the analyzer 

A few random pictures from various stages and explanations


The design is pretty simple. The idea is to make three modules or subsections

  •  DDS generator (ad9850)
  • A logarithmic detector (ad8307)
  • A simple resistive bridge 
  • A Nokia LCD for display
  • A Bluetooth serial module for wireless/remote use
Details of most of these components and sections can be read in some of my old posts

Make a simple PCB (around 5cm X 9cm)

This was fun (more on this here) But at the end of the game, i realized that I forgot to mirror the atmega328 and BNC connector! 

So much frustration but solved by bending all the 28 pins (yes!!) of atmega328pu carefully and upside down. BNC socket was moved from a PCB mount one to box mounted.  But a good learning point and was ok for home etching. If I send to fab, would have been a loss of 10 PCB

Layout and pcb for proto

And here is the trace

Layout with errors
And some mounted pictures and post assembly with dirty hacks


log detector


program test and boot load

ATMEGA pinouts for reference

1) I forgot to accommodate a solution for power/battery (ended up using a small power bank)
2) Need some more space for a second detector and may be some extra switching for signals (now it is with jumpers)
3) Add wire mesh to the plastic box
4) Write it a bit more cleaner.. (sorry about it, a lot of other stuff cramming up)

More details will be updated soon. 

Thanks for the read

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