Bob
The 12 MHz crystal filter is quite narrow. If the bfo is way off,? the signal will be highly attenuated by the shape of this filter. Second,? the receiver has less total gsin than some receivers so a good antenna is needed, not just a short piece of wire. My bfo came way off and it wasn't easy to get it aligned. When aligned, big signals will be quite loud in headphones needing the volume control to be set quite low. Weak signals might need near full volume. If you like to use a speaker, you may wish to use an amplified one, there are many inexpensive ones out there. But first important to align the bfo.
Curt
