11 May 2010

4W TX for sub-9kHz experiments

Attached is a picture of the "transmitter" I'm using for my ground and induction communications tests. It uses a TDA2003 audio IC into a toroidal step-up transformer that can match from 10 to 150 ohms. Not sure of the transformer type which came from an old Pye Telecom PMR radio, possibly an M206, Whitehall or similar (it was used on the audio stages). I haven't yet tried listening with an active probe antenna to see how that would perform. Time is limited, so further tests may have to wait until the end of the month. Best range so far, receiving "by ear" on a loop antenna, with no clever selectivity or signal processing, is 0.35km.
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2 comments:

  1. AnonymousTue May 11, 01:03:00 pm GMT+1

    Hello Roger

    I have got some step down transformers out of a Philips Public address system to step the 100v line down to speaker matching
    Impedance.They would make ideal step up transformers.
    I have seen a Quad Amplifier with
    the 100v line option fitted.

    Tony

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  2. Roger G3XBMTue May 11, 05:28:00 pm GMT+1

    Thanks for the tip Tony. I'll try winding a toroid step-up transformer with a wider range as the maximum tap on my present output transformer is 150 ohms, and this isn't enough.

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