Help with a RACHEL AND STEVE HAGEMAN, BFO

[WM6]

It is absolutely incopetent to design operating point of such amplifier near to transistor saturation, because the gain is minimall and (if oscillation starts) the circuit can not deliver enough amplitude. ...........................

Note that there is no information how to design the operating point of transistor for reliable start of oscillation and for large amplitude (because the author is not radio amateur :-).

Despite of what "competent radio" AMATEUR PHILOSOPHERS says, Hageman (a little modified Clapp - not Colpitts!) oscillator works very well.
Maybe not in world of lost in space simulations, but in real world it works (oscillate) with appropriate, clear and stable signal, as shown on pictures:

[mikebg]

Despite of what competent "radio" AMATEUR PHILOSOPHERS says, Hageman (a little modified Clapp - not Colpitts) oscillator works very well.
Maybe not in world of lost in space simulations, but in real world it works (oscillate) with appropriate, clear and stable signal, as shown on pictures:

Nothing new! The authors insist that the circuit works wery well:
http://www.geotech1.com/cgi-bin/page.../edn/index.dat
Then why this thread was started?
Note what is written in the page 2:
"The Q2 beat oscillator uses a similar Colpitts design".
Since you are not philosofer, please help Beach to make the circuit operating.

[WM6]

"The Q2 beat oscillator uses a similar Colpitts design".

Since you are not philosofer, please help Beach to make the circuit operating.

As competent radio amateur you have to know that this is not Colpitts but Clapp, no matter what author say.
In general (block scheme - you know) all oscillators are similar.

I tried to help Beach in past days over PM.

Right question is: why you do not help him with your working competent design?

[mikebg]

As competent radio amateur you have to know that this is not Colpitts but Clapp, no matter what author say.
In general (block scheme - you know) all oscillators are similar.

I tried to help Beach in past days over PM.

Right question is: why you do not help him with your working competent design?

I agree with you that in general all oscillators are similar. This relates also for design of transistor operating point.
As you know, my design of search oscillator uses separate TX and RX windindins placed near to induction balance.
http://www.geotech1.com/forums/showthread.php?t=16929
What amplitude of oscillation shows your experiment with Clapp oscillator?

[Qiaozhi]

As competent radio amateur you have to know that this is not Colpitts but Clapp, no matter what author say.

To be pedantic ... the author is not totally incorrect, as the Clapp oscillator is a member of the Colpitts family. You can see this in the circuit diagram, as the feedback voltage is derived from a capacitor network, unlike a Hartley oscillator where the feedback voltage is derived from an inductor network.

[WM6]

What amplitude of oscillation shows your experiment?

Genau 500mV pp measured at coupling capacitor (on mixer side). Without very small (2.2pF) coupling condenser I got emitter amplitude 2.6V pp (the same direct on coil).

This is single oscillator operation, without mutual inductance with other oscillator.

Maybe it seems a little low, but high signal amplitude is not general answer to better detecting. There are many factors that changes with voltage changing and not every with positive effect in detecting.

Example: in bad ground (Fe mineralised) higher voltage leads to higher soil magnetisation (with higher remanent magnetism) which invalidate all expected results of higher amplitude. And this is not only problem of increased amplitude.

[WM6]

To be pedantic ... the author is not totally incorrect, as the Clapp oscillator is a member of the Colpitts family. You can see this in the circuit diagram, as the feedback voltage is derived from a capacitor network, unlike a Hartley oscillator where the feedback voltage is derived from an inductor network.

I know, but in amateur radio world: Clapp is Clapp and Colpitts is Colpitts. Very distinctive - question of way of single C coupling (decoupling).

[mikebg]

I know, but in amateur radio world: Clapp is Clapp and Colpitts is Colpitts. Very distinctive - question of way of single C coupling (decoupling).

I agree that this is Clapp oscillator.
Here is circuit diagram of an absobtion metal detector. IMNHO the operating point of Clapp oscillator is competent designed. Source:
http://iloapp.marcboon.com/blog/rfid?Home&page=4

[WM6]

Here is circuit diagram of an absobtion metal detector.

Great project of Marc Boon. Thanks for info mike.

Tuned at too high frequency to be suitable (in present schematic) for metal detecting / prospecting.

[mikebg]

Great project of Marc Boon. Thanks for info mike.

Tuned at too high frequency to be suitable (in present schematic) for metal detecting / prospecting.

See the operating point: