30 Jan 2014

Crystal sets

It is some time since I built a crystal set, but these are great fun and very easy to build.  Remember you are using the TX station for all power. There are no DC supplies in a crystal set.

Most designs are still for Medium Wave reception, but I had most fun with short wave designs based around T50-2 (red) or T50-6 (yellow) toroids which allow small hi-Q coils to be wound. Larger T68 or larger diameters are also suitable.

There are PLENTY of resources on the internet (just Google "crystal set" ) but a typical one is:
http://www.mds975.co.uk/Content/crystalsets2.html .  Never assume crystal sets are useless: I have copied stations (not via relays) directly from all over the world including All India Radio, Radio Australia and Cuba.  The short wave design  used just a handful of parts. Signal levels will be in 500uV to 2mV region. A good crystal set design can detect down to about 400uV or less, but a lot will depend on your earpiece(s) and your ears. One has to ride QSB as some distant stations appear to be co-channel with less distant stations.

It would be fun to build a multi-band (LW, MW, SW and  VHF) design some day. There are even designs for Band II FM using slope detection. They should work well on VHF aircraft band which is still AM with local airports and planes. I have never seen an aircraft-band design. You can always add a small audio amp, but this rather defeats the purpose of a crystal set.

See also my own website about crystal sets :https://sites.google.com/site/g3xbmqrp3/hf/crystalset .

1 comment:

Paul VA3PAW said...

This design uses LM358 amplifier:
otherwise, the volume would probably be way too low...