How this circuit like?

[yhl]

[kt315]

can you tell more about yourself? how old are you? are you communist Chinese or capitalistic Taiwanese?

[mikebg]

KT315, does it matter what is yhl's age and party? The important thing is that he wants to be like us, to learn something, to receive information. How would you feel if they ask if you are a retired Red Army officer and if you have membership in a fascist party? Yhl has already 76 postings in this forum. Note that recently he writes in more understandable English. Your questions are not offensive to refuse him to start new threads in this forum. Hang on as a modern European, rather than fascist in 30-ies years of last century.

Yhl, your circuit is a BFO MD. The reference oscillator operates at 4th or 5th harmonic of search oscillator. Frequencies are for example 455kHz and 80 ... 120kHz. The original article of this project was published in German magazine "Funkschau" May 1984. The circuit above is extracted from a reprint made in Chech magazine "Amatérské Radio" April 1990 page 126.
The oscillogrames represent:
1. Reference oscillator output,
2. Search oscillator output,
3. Output of IOз, pin 1,
4. Voltage across headphones.
Headphones should be piezo or high impedance.

[kt315]

fascists, you mean hazi here probably, gave people the work places, got up the economic, developed the industry. now I have not the work! I have been retired without my wish! so think what you write about.

[mikebg]

Yhl, when you post large images, try to reduce their width to 1024 pixels if the heigth is not large (or their heigth to 640 pixels if the width is not large). I use for Resize/Resample of images the free program IrfanView. It has an option "Preserve Aspect Ratio" and you easy reduce only width or only height.
Compare my posting below with your posting above. Participants in this forum can see in my posting the whole circuit diagram without scrolling.

[yhl]

Thank you MIKEBG.

Thank you MIKEBG. Hope this is a good circuit. I need you to help build
I have a site inside a circuit
http://www.pchelar-probvaisambg.com/..._68_spisak.htm

[mikebg]

Thank you MIKEBG. Hope this is a good circuit. I need you to help build.

Yhl, for me a good circuit operates in a principle that can not be improved.

You found a Bulgarian site for beginning builders. It shows old primitive operating circuit diagrams. However you're not beginner because are a participant in our forum. Our participants already know the shortcomings of the conventional BFO type circuits and methods for their improvement. As you follow postings for BFO on the forum this year, already know that the circuit diagram, you choose for building, has at least 4 shortcomings that can easy be improved:

1. Search oscillator operates with sensing head type MONOCOIL. For better sensitivity, the search oscillator should use separate TX and RX coils placed almost in induction balance. Rev. Thomas Scarborough reinvented and renamed the circuit of Leslie Hoggard as "CCO metal detector", but this is not whole detector, only the sensing part.

2. Search oscillator excites environment and targets with wery low TX power. For better sensitivity we need a powerful oscillator builded with an audio IC for example LM386, which drives TX coil with its internal noise as if it is a loudspeaker. Leslie Hoggard also uses LM386 in project HOUNDOG. Even Rev. Thomas uses it in an of his projects for CCO.

3. Search oscillator operates at too high frequency (about 100kHz), which causes large GND signal. To reduce GND signal, we should use two RX coils connected as TWIN LOOP and connect large capacitances for LC circuits to tune them for lower resonance frequncy, for example 14kHz.

4. Since reference oscillator can't compensate instability of search oscillator, the operator must often use both buttons for coarse and fine adjusting. However we know that no need of such buttons. We can use a PLL IC as reference oscillator, for example CD4046. Such IC uses Macario in his project "Discriminative metal detector". The BFO principle with PLL reference oscillator operates as very sensitive motion type detector.

Here is a MD circuit with CD4046 from above Bulgarian site, but it operates at high frequency. The circuit of Macario is much better.

[yhl]

Why do all the mixer with the CD4013?


Why do all the mixer with the CD4013?This can transform CD4013 mixing it?

[mikebg]

Yhl, CD4013 contains two D-type Flip-Flops. The flip-flop makes level change of outptuts Q and Q when both inputs (R and S) are zero as shown in the truth table below. Its operation as mixer in BFO MDs is represented by oscillogrames in postings #1 and # 5.

[mikebg]

However, if you use CD4046, no need of mixer, because this IC has an output noted as "phase pulses".

When you use a PLL circuit for reference oscillator, no need of knobs for adjustment. These knobs are noted as "jemné" (fine) and "hrubé" (coarse) in postings #1 and #8 above. The circuit in #8 below also needs such adjustments with C1 (fine) and with core of L1 (coarse).

As shown below, the circuit of Macario has only a switch S for fast setting at beat frequency zero, when you adjust R1. However S and R1 are not buttons for operator; they are inside control box.

[mikebg]

can you tell more about yourself? how old are you? are you communist Chinese or capitalistic Taiwanese?

After long time in production with flat legs (as shown below), transistor KT315 is now produced in case TO92:
http://www.transistor.by/i/pdf/kt315.pdf

In the past century, 2N3904 was the most widely used cheap transistor for general purpose in the United States.
The same can be said of the transistor KT315, widely used in the ex country Sovjet Union or USSR. Lithuania, Belarus and Russia participated in this "union" (Bulgaria was a secret participant :-). Now there is no the country Sovjet Union, but in Belarus remains production of KT315.

What means nickname "KT315"? Is it nostalgia that feels Anatolij Kutovoj for communism (when there was no unemployment in the Lithuania) or nostalgia for nonexisting powerful Soviet Army (where Anatolij had to fulfill his military service about 30 years ago)л

Not! The alias KT is simply a school nickname comming from Kutovoj.
Dear KT315, the letter "T" is not from of yours first name because it is in the middle of "AnaTolij". Ask your ex classmates to tell you that KT comes from your last name, but this is absolutely not important. Important is what participants in this world forum feel for a gentlemen known here as KT315.

I have feeling that Anatolij is an excellent expert in this hobby, sharing his knowledge almost with all.

But why "almost"?

Because there are several participants who do not feel the same as me.
If I was drunk and I had written (in such a condition) something similar to posting #2, once sober I'd be ashamed. I'd apologize to Yhl and ask the Administrator to delete that posting.

As Anatolij not guilty, that was born in the communist country Sovjet Union, upposed to serve in the Red Army, and Yhl not guilty, that is born Chinese.

However, everyone (even drunk) is to blame for his behavior to others.

[maikl]

After long time in production with flat legs (as shown below), transistor KT315 is now produced in case TO92:
http://www.transistor.by/i/pdf/kt315.pdf

In the past century, 2N3904 was the most widely used cheap transistor for general purpose in the United States.
The same can be said of the transistor KT315, widely used in the ex country Sovjet Union or USSR. Lithuania, Belarus and Russia participated in this "union" (Bulgaria was a secret participant :-). Now there is no the country Sovjet Union, but in Belarus remains production of KT315.

What means nickname "KT315"? Is it nostalgia that feels Anatolij Kutovoj for communism (when there was no unemployment in the Lithuania) or nostalgia for nonexisting powerful Soviet Army (where Anatolij had to fulfill his military service about 30 years ago)л

Not! The alias KT is simply a school nickname comming from Kutovoj.
Dear KT315, the letter "T" is not from of yours first name because it is in the middle of "AnaTolij". Ask your ex classmates to tell you that KT comes from your last name, but this is absolutely not important. Important is what participants in this world forum feel for a gentlemen known here as KT315.

I have feeling that Anatolij is an excellent expert in this hobby, sharing his knowledge almost with all.

But why "almost"?

Because there are several participants who do not feel the same as me.
If I was drunk and I had written (in such a condition) something similar to posting #2, once sober I'd be ashamed. I'd apologize to Yhl and ask the Administrator to delete that posting.

As Anatolij not guilty, that was born in the communist country Sovjet Union, upposed to serve in the Red Army, and Yhl not guilty, that is born Chinese.

However, everyone (even drunk) is to blame for his behavior to others.

Does not have to ask the administrator to delete the message. Whoever wrote the message can I change it whenever wishes (for example, can delete all and put "?"). Let us return to the topic mikebg.Tell our friend yhl that the classical BFO will not reach that far(It is obsolescent type detector).Since he is searching for ordinary iron and there was not substantial discrimination against those he recommended a PI detector.Me PI detectors are not particularly interested in (because of poor discrimination, and high power consumption).You are better experts than me and he therefore recommended a PI detector that is easy to manufacture and handling.

[mikebg]

Maikl, let KT315 and Admin try to understand the problem since I and you can not express in good English.

As you know, I'm only a hobbist designer, but I know how should operate the future most sensitive metal detector because I'm familiar with design process. My hobby is to design transceivers for QRP amateur radio. The design process starts with analysis of ideal operating principle in frequency domain and composition of best operating block diagram. I know three main things for block diagram:

- The gain of RFA in front end of RX should be limited by noise, not by EMI AIR and GND signals.

- The real GND signal should be used for referece voltage at synchronous demodulation.

- After demodulator we need a band pass filter for damned low frequencies (below 1Hz).

The block diagram can not be designed with experiments and SPICE. Only knowledge and thinking in frequency domain can help to improve sensitivity of metal detectors. I can not see discussion on block diagram in the metal detecting forums.

Note that your above posting is a step in this process. You start to analyse different operating principles and to show their drawbacks. However your step and its direction are made in darkness because you are not thinking in frequency domain.

In frequency domain exist only two types metal detectors: narrow band and wide band. Attached figure illustrates TX current at both cases. For symbolic explanation I use sinc pulse as nonsine induction, because it generates flat frequecy spectrum in operating band.

I know that you wont agree with me, but wide band metal detectors (as conventional PI) are more "discriminative" (a bad term) because deliver more information for spectral characteristic of target. However the term "wide band" means for a designer minimal stray capacitances and increased energy dissipation because he need damping resistors to discharge stray capacitances.

Narrow band metal detectors are energy efficient because they use tuned circuit in TX. Stray capacitances are not important. A single frequency metal detector delivers information for only a point of target's spectral characteristic. That means it is less informative (discriminative) because TX operates with sine induction.

CONCLUSION: A properly designed PI metal detector should discriminate much better than a VLF MD. Since I hate the bad terminology used in this conclusion, I will expain it with other words:

If we need more information for targets, the TX coil should excite environment with nonsinusoidal current.
The radiated magnetic field should contain frequency band in which spectral characteristics of targets are different. In ideal case the TX current is as sinc function.

However since metal detectors are only narrow band and wide band types, how to classify a metal detector with search oscillator (BFO or frequency shift MD)? I know how search oscillator excites targets.

[kt315]

Mike, you waste your time on BFOs. maybe this guy tomorrow will reached Tinkerer level and WILL GIVE YOU absoliutely fresh info from Chinese hight tech electronincs... I very hope it will be... IMO you do NOT up his level - you are only getting DOWN your level to his one. this guy is similar to - Chinese adage, by the way - "to try find out Black Kitty in the dark room" - and you absoliutely despairingly try to help to find this black cat.
I have gave all info on Chinese metal detector MD-5008 as much as I only can able. from PCB layout, tracing, the schematic, the coil inside etc. this detector is best for all metal types. has full static mode. CHINESE detector.
I am not Confucious... but believe me now - there are much knowledgeable people in the China...

sincerely Yours

[maikl]

mikebg I also agree with the kt315 : "BFO has no future" (regardless of the frequency). Can improve sensitivity and a bit of stability for small objects on the surface. In my opinion, these projects have a futurethe as shown (the demands of the average hunter). I am interested in your opinion. Not because it comes to your countryman, but seems really interesting in every respect.