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Old 30th Dec 2009, 1:21 pm   #12
dominicbeesley
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Join Date: Nov 2004
Location: Hebden Bridge, West Yorkshire, UK.
Posts: 1,885
Default Re: Homodyne/Direct Conversion

Hello all,

Interesting thread. I built a homodyne similar to the one here: http://www.vintageradio.me.uk/radconnav/transtrf/ (March 1972 The Radio Constructor, G. W. Short). I chose this as it seemed simple!

It worked ok but needs a fairly strong signal and <90% modulation or it can go a bit odd. The sound is a bit "quacky" and adjacent channels can be a problem. However I built it as a receiver for NBTV signals where - even though it sounds poor it outperforms all the other receivers I've tried. Presumably due to its wider bandwidth and the fact that it doesn't muck about with the phase of the signals - important for vision....

Next receiver I make for NBTV I intend to try a crystal ladder filter at say 1MHz to extract the carrier and a PLL type arrangement with local oscillator to demodulate - not sure how well this will work with VSB signals but it should be interesting to find out...

Dom
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