Popular Electronics, Feb. 1969

[mikebg]

The reinvented block diagram

WM6, thank you. You did a great job and showed how we can do translations from pdf.
Yesterday the (R) EMI group draw a block diagram, which differs from that described in the article. Now, I expect they to write a description of their block diagram, which will probably be quite different in principle. The attached diagram represents an oscillator. It will oscillate at a frequency for which phase shift in feedback loop is 0 or 360 deg. The reinvention continues.

[WM6]

Now, I expect they to write a description of their block diagram, which will probably be quite different in principle.

We all expect some detailed description too. And at the end working circuit diagram. Thank you in advance.

[Esteban]

Here some complete Popular Electronics old articles, 2 in reference MD. But no the 3 coils MD. Maybe I have in English the original. I'll search for it.

http://www.swtpc.com/mholley/Popular...lectronics.htm

[Qiaozhi]

Here some complete Popular Electronics old articles, 2 in reference MD. But no the 3 coils MD. Maybe I have in English the original. I'll search for it.

http://www.swtpc.com/mholley/Popular...lectronics.htm

Thanks.

Very interesting.

[WM6]

Same coil arrangement.

Hi Qiaozhi,

what is your L-calculator saying about inductance of coils?

In my calculations I get:

Rx=18mH (x2)
Tx=36mH

[Qiaozhi]

Hi Qiaozhi,

what is your L-calculator saying about inductance of coils?

In my calculations I get:

Rx=18mH (x2)
Tx=36mH

OK - I've looked at this very quickly.

According to your translation, the horizontal coil has 470 turns and the vertical coil has 870 turns. The diagram in the article shows: horiz = 3.8125" (96.8mm diameter) and vert = 1.5" (38.1mm diameter). If we assume 0.2mm thickness for the wire, then:

Horizontal = 46.9mH
Vertical = 46.3mH

Seems quite different to your results.

[WM6]

Horizontal = 46.9mH
Vertical = 46.3mH

Seems quite different to your results.

Please check it again. You use diameter as circle (e.g. Rx diameter = 96.8mm) but it is not in round form. Rx coil outer measure of (horizontal coil) are: 3 3/4" x 2 1/4" this can not give us (circle) diameter of 3.8125". Can you check this again?

[Qiaozhi]

Please check it again. You use diameter as circle (e.g. Rx diameter = 96.8mm) but it is not in round form. Rx coil outer measure of (horizontal coil) are: 3 3/4" x 2 1/4" this can not give us (circle) diameter of 3.8125". Can you check this again?

If RX coil is 3.75" x 2.25", then circumference is 12" (304.8mm). If this was a circle it would have a radius of 97mm. The inductance is then 47mH.

[Gwil]

I don't think that the inductance of a non-circular coil is the same as a circular coil with the same circumference. Isn't the inductance a function of the area it encloses? Squeezing a circular coil until the sides touch would dramatically reduce its inductance.

Gwil

[Qiaozhi]

I don't think that the inductance of a non-circular coil is the same as a circular coil with the same circumference. Isn't the inductance a function of the area it encloses? Squeezing a circular coil until the sides touch would dramatically reduce its inductance.

Gwil

True ... but my coil calculator only handles circular coils. Therefore it's just an estimate. Maybe I should recalculate, keeping the enclosed area the same.

[mikebg]

Block diagram

Block diagram of IBR (Induction Balanced Regenerator)

Block diagram (shown above in posting # 16) is similar to a blocking generator - a wideband amplifier with regenerative feedback via mutual inductance. Without tuned circuits, it will generate pulses as multivibrator. To generate as a sine wave Meissner (Armstrong) oscillator, needs a tuned circuit, ie to one of the coils to be connected capacitor to obtain the required phase shift. The mutual inductance M between coils L1 and L2 shoud be minimal to increase the modulation index of target signal. This means induction balance or minimal K (coefficient of coupling).
The feedback loop is closed in two ways:
- The upper signal path is through mutual parameters M, L, R, C between L1 and L2. The change of TX current in L1 induces voltage in RX coil L2 by mutual inductance M. The phase of mutual induced signal is independent on frequency. It remains always in quadrature, ie in phase lead 90 deg to excitating TX current. This voltage is shown in complex plane below as a signal AIR. Each frequency represented by a point in streight line 1. When frequency increases, the point moves upward.
NOTE: We can close feedback loop by adding an additional network or mutual parameters L, R, C. Thus the phase of AIR signal can be made frequency dependent. This is done by C7 and R5 in circuit diagram (shown above in posting #5). The additional closure is not shown in the above block diagram.
- The lower signal path is through block TARGET. The phase characteristic of TGT signal can be extracted from curved line 3 for ferrous metal. When TX frequency changes from zero to infinity, his point on the curve moves in shown direction. Thus, at ferrous target, the signal can have any phase in the range from +90 deg in 1st quadrant to minus 90 deg in 4th quadrant. At nonferrous target (shown with curved line 4), the phase may be in 4th quadrant only. The signal can have any phase in the range from 0 deg to minus 90 deg. Note that ferrous and nonferrous conductors have a cuttoff frequency at which phase lag is 90 deg, but only ferrous target has a resonance frequency, at which visual phase lag is zero. This is quasi-resonance because phase lag is 360 deg.
The system may oscillate if it has 2 conditions are met:
1. Phase delay must be 360 deg or a multiple of 360 deg for some frequency . For a given target, this condition can be set in block PHASE SHIFT, which contains a PHASE control.
2. The gain of closed feedback loop must be greater than one at the some frequency. For this purpose anywhere in the feedback loop must be connected a potentiometer (attenuator) GAIN control. This is R9 in above circuit diagram. If the gain of closed loop is greater than one for more frequencies, the circuit will generate as multivibrator.
The sensing network in above block diagram can not serve for visual analysis because is too simplified. We should connect a comprehensive block diagram of sensing network containing ground with target buried in it and two RX coils. The TGT signal undergoes changes due to double pass the energy through the ground.

[WM6]

2. The gain of closed feedback loop must be greater than one at the some frequency. For this purpose anywhere in the feedback loop must be connected a potentiometer (attenuator) GAIN control. This is R9 in above circuit diagram. If the gain of closed loop is greater than one for more frequencies, the circuit will generate as multivibrator.

.

Hi mikebg

I don't understand this. Mean some -> single or sole frequency?
Indeed some or more may mean here the same thing.

[mikebg]

WM6,
The gain of closed feedback loop is a frequency or time dependent function. In order for a circuit to start oscillate, it must satisfy the Barkhausen criteria:
1. The loop gain must be >1 for one frequency or for more frequencies and
2. The loop phase must be a multiple of 360 degrees.
For example, if we have microphone and loudspeaker set up in an auditorium, the feedback is provided by sound waves traveling from the loudspeaker back to the microphone. At what frequency will oscillate this system depends on all stages in the system, giving phase delays. If you do experiment with such a system, would establish that the frequency varies when changing the distance between microphone and loudspeaker. This shows at what frequency Barkhausen requirements are met. Search WEB for "Barkhausen criteria", "Barkhausen criterion", "Barkhausen stability criterion", "Nyquist criterion", "Oscillator theory".
In our case, the frequency of oscillation will depend on the frequency properties of target and ground. All four possible properties are shown in the upper polar plot. Question arises: "How to make the frequency of oscillation depends only on the metal of the target?" We must combine the ground line with the curved line of target because the target is buried in ground.

[Esteban]

Have the complete article typying by original in pdf, with constructional details and many info, 1.7 Mb , but don't have special pregorratives for to post here. Maybe some admin can do it. The sample:

[Qiaozhi]

Have the complete article typying by original in pdf, with constructional details and many info, 1.7 Mb , but don't have special pregorratives for to post here. Maybe some admin can do it. The sample:

Hi Esteban,

Please email it to me at [email protected] and I will upload it here.