I don't know how dirty, it contains the fundamental (the receive carier), the reference (local oscillator), the sum and product of the two mixed signals. Once you grasp that concept, you understand how a radio receiver works. Delving deeper off topic, since you want the modulated information (in the case of an AM broadcast receiver), the reference oscillator (or local oscillator) generates a frequency 455 khz above or below the desired listening signal. The "intermediate frequency" amplifier passes only the sum or product and attenuates the local oscillator and receive frequency. This acts just like a hi/low pass filter more commonly known as a band pass filter. It also increases your selectivity by the sharpness, or stages of IF amplification. The signal is then demodulated by means of a diode to remove the IF frequency and what is left behind is your AM audio information that was broadcast.... There.. now you know how a superhetrodyne AM receiver works. Rick C. Chief Engineer - WTRM-FM Denny Esterline wrote: > When you mix the freqs you get a very dirty signal that contains the > sum freq (extremely high) and the difference freq (low, usually audio) > Considering the enormous difference between these two components they > are very easy to separate with lowpass filters. > > (do I here a "click" yet?) :-) > > -Denny > > ----- Original Message ----- > From: "Tim Hart" > To: > Sent: Wednesday, November 12, 2003 11:21 AM > Subject: Re: [OT]: Simple questions... > > The heterodyne just sounds counterintuitive.... > Ultra High + Local High = 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 > > > > I appreciate the help!!! > > Tim > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu