4SQRP recently announced another addition to their line of kits for the QRP’er and home-brewer. This one particularly caught my eye, for reasons that I’ll explain in the next paragraph.
Designed by David Cripe NM0S, the Hi-Per-Mite provides a -3dB bandwidth of 200Hz with no ringing. The center frequency as supplied is 700Hz, but this is user selectable at time of building. The filter response is bandpass as opposed to lowpass, meaning that it will help to filter out any remaining traces of 50Hz hum you may have in that homebrew direct conversion receiver of yours (or an older vacuum tube receiver perhaps?) After the filter is an LM386 audio amplifier with a gain that, once again, can be set by the builder. If you set it to the maximum of 50dB, you have a combination bandpass filter and audio amp that can provide the complete audio chain for a regenerative or direct conversion receiver. If you already have the receiver, you can set the gain to a lower figure and you still have a really useful CW filter.
I’m thinking that for those who like to build simple receivers, this could be a very handy kit to have around.
All this for US$19 including shipping within the US (more for overseas).