Student requesting EDN design community help

-December 11, 2012

Editor's Note: An embedded systems Masters level student decided to build a simple wireless sensor node. For that he need to build a very simple 433.92MHz transceiver (based on a SAW resonator) which is powered by a 3V coin cell. Any suggestions folks? Your solution will be featured on the home page of EDN and in our Fun Friday newsletter. Here's his problem, in his own words:

As a problem of energy saving, the super-regenerative receiver from EDN Design Ideas in 2006 seems an ideal choice, that is for what I tried to build a receiver using the circuit I found on the web. Really I built just the detector of this circuit (red zone on the schematic attached), and I used an oscilloscope to visualize the output.

The problem I found was at the step of tuning the variable capacitor (I used a variable capacitor instead of a variable inductor), it's difficult to get it stable and when I release it the frequency changes(the capacitance of my hand disturbs the tank circuit) and the sensitivity was poor(just few meters),all this knowing the consumption was average 150uA @3v.

My ultimate goal is to get this receiver working with a sensitivity of 3Om and consumes less than 200uA.

So now I want to know:

1. How to avoid the disturbance of the tank circuit?

2. If I decide to use another HF transistor, how to modify the resistors r5 & r6?

3. How to increase the sensitivity of this circuit to achieve 30m (with minimum energy)?

Click on image to enlarge

I ask the EDN design community to help this young engineer and give him a great lesson in the comraderie that we EE's have worldwide. Please send your comments and advice in the form of comments, schematics, scope shots, etc. on this blog.

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