The heterodyne just sounds counterintuitive....
Ultra High + Local High =3D Low?

AM is a good example....I've not actually built an AM radio...but I guess =
it does the same thing.  Turns 600 AM into something I can hear.  One =
person out on the web converted an AM radio into a heterodyne....

I'll keep reading....it will "click" sooner or later....
Once again Thanks for the help!!!
Tim

>>> rixy@VVALLEY.COM 11/11/03 04:22PM >>>
Just looked at the bat detector schematic. It's just lie I explained. The =
LM567 is the oscillator. Q1 and Q2 make up a preamp and high pass filter. =
Both feed the fet mixer Q3 via R7/C2 and R11/C5. The resultat "tone" or =
ticking is amplified by U1. Simple.
Rick

Tim Hart wrote:

> I found some "Bat Detector" circuits that seem to be exactly what I'm =
wanting to do.  I'm still lost as to why a local signal mixed with an =
ultrahigh signal makes something you can hear?
>
> They are used an LMC567 "Phase Locked Loop IC" to make the local =
oscillations.  Which is Greek to me...  I've used the LM386 before so I'm =
cool with that...but the rest still doesn't make much sense.
>
> Maybe you can make sense of it...
> http://www.njsas.org/projects/bat_detector/populel_sch.html=20
>
> I appreciate the help!!!
> Tim

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