BFO TYPE LOCATOR

[gold24h]

I have built a bfo and radio pistol type locator,the bfo has an external coil about five inches around with seventy turns of wire,around the edge of coil not touching the wires in the coil i have a 1/8 diameter aluminum rod that is connected by a cable to the antanna of an am fm raido,the question is how do i tune the bfo,do i tune it to null not making any sound in the speaker or do i tune it just like a bfo metal detector,just past the null point making a tone.Another question,the radio,it will pick up the bfo tone any place i tune the radio any channel,am or fm.Am has a lot of blank channels but fm is almost full of stations,could somebody give there advice on how to set this type of locator up.