Envelope follower

[Overtheedge]

Good book, but ...

Page 36: envelope follower.

How about a couple or six paragraphs of explanation of a seemingly simple circuit that I intuitively understand, sort of, uh, er, not really?
Try a web search for "envelope follower".
I did for over four hours and that is why I'm asking.

Just re-read paragraph 2 and 3 and then please explain it to me. From a simple diode passing only the positive portion of the signal to the neatness of the CA3240E IC. Glad you understand, because now we are gonna change the time constant.

Shall we move on to Chapter 13 and 14 for 50 pages of this is nonsense and we are gonna show you how to prove if for yourself. Yah, I'm not so happy that you spend so much time on this and not explain the Automatic Tracking Circuit on page 36.

The basic circuit is used several times in the book and it would be nice to understand the basics. I mean I have several books open and no such animal unless I toss out the feedback capacitor and direct couple the output to the negative input. It is like some kind of a weird cascode circuit with a time constant that I assume is based upon R3/C3.

Just a few paragraphs would make this much easier for me to understand.

eric

[Qiaozhi]

Just a few paragraphs would make this much easier for me to understand.

eric

The purpose of the envelope follower (Fig. 4-4) is to measure the amplitude of the search oscillator. Depending on the value of C3, you can change the time constant of the circuit such that the output of IC1b "follows" the amplitude at either a faster or slower rate. This circuit is a modified version of a precision peak detector, but without the complication of providing a reset circuit to discharge the capacitor. In this application we're not concerned about precision, as the search oscillator output will always remain at a relatively high voltage. Also, please note that the opamp is being driven from a single-ended power supply, and therefore D1 and R3 are needed to block the negative part of the waveform that is fed to the non-inverting terminal of IC1a. It can then readily be seen that IC1a, D2 and C3 would form a simple peak detector if the cathode of D2 were connected to the inverting input of IC1a. The opamp IC1b (unity gain amplifier) was added as a buffer to prevent the sensitivity pot (VR1) from discharging C3. Since there is no reset circuit in this design, the charge on C3 gradually leaks away due to the input bias current of IC2b. The design uses two of these envelope followers, one with a fast time constant (C3 = 10nF) and another with a much slower time constant (C4 = 10uF). By feeding these signals into a comparator, the slow tracker will act a reference signal for the fast tracker, effectively eliminating problems due to drift, and creating a simple switch-on-and-go detector.

[Qiaozhi]

Shall we move on to Chapter 13 and 14 for 50 pages of this is nonsense and we are gonna show you how to prove if for yourself.

The information on Long Range Locators, Dowsing, Treasure Auras, and the so-called Pistol Detector, were included for completeness. Whether we like it or not, LRLs are widely advertised as "fact" by their manufacturers; and it was felt at the time that an alternative view needed to be presented. There are whole books on the subject of treasure auras (for example) which I totally agree are complete nonsense. However, Chapters 13 and 14 of ITMD are not nonsense as they present the real truth about these subjects. Not only do we provide several experiments for you to try yourself, but there is also a "working" design that costs a lot less to build than buying an equivalent commercial all-electronic LRL. Not only is it a fraction of the cost, but it will equal or even exceed the capabilities of the commercial units.