MSF Radio Receiver

Posted on Feb 7, 2014

This page documents an older version of the project that proved very unreliable. This is (still) an ongoing project when I get free time, so I post periodic updates here until I get a proper design/rig and eventually create a new page for it (with pictures of course. ) Current Status (January 2010): During the time off at Christmas I`ve made some r

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eal progress on my dsPIC superhet design. Still a fair way to go, but I have a test rig knocked up with a PIC-controlled VFO and LCD interface among other things. The next stages - when time permits - will be implementing a proper tuning mechanism and the Huff-Puff stabiliser for the VFO (both in firmware), and then designing the crystal filter and amplifier hardware blocks. Eventually, I will create a page for the project that will replace this one. Current Status (October 2009): I have found a single-pole crystal filter to be unreliable - the bandwidth is far too narrow so the on-off transitions are so slow that the carrier never decays; this is no good for the double bit transmissions. I`ve also discovered that the transitions can be improved by lower crystal termination impedance, but that`s more crystal drive and it wrecks the filtering properties. This is no good, especially when the receiver is supposed to operate in a noisy PC room; a better way needs to be found. I`m toying with the idea of a simple dsPIC-based superhet; two NE602 mixers (one for up-conversion for filtering, one for converting back to baseband) and a few higher frequency crystals (greater bandwidth and more design info available) come to about the same cost as the low-frequency crystals plus the number of inductors I was using for low-Q pre-crystal filtering. Besides which, the inductors tended to pick up a lot of noise and the filters needed even...

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