Magnum on steroids!

[ivconic]

Can anyone tell me if there is an advantage (or disadvantage) in using a Magnum type common base amplifier as the first stage of the receiver, rather than an op amp?
Thanks.

I noticed interesting thing coincidently; even when TX is not connected; RX will still work!? It will detect ferrous objects at decent distance!
Iron pliers is detected at 40cm in air! With strong audio response!
RX is untuned, wideband. Tolerant. Low impedance input and high impedance output.
I guess it is much easier to make it work in diy arrangement. Very sensitive.
I would ask the same question to Dave Johnson about indeed splendid solution at 1225, 1235 and similar RX frontends.
At SMW exactly that part is taken and copied from 1225.
Later on i made version with opamp front end just to see the differences. Original 1225 version was superior in all the aspects.
Solid state rules!

[Gwil]

Thanks, very interesting. However is the Rx really untuned? Doesn't the Rx coil and the 473 capacitor form a series tuned circuit?

[ivconic]

Thanks, very interesting. However is the Rx really untuned? Doesn't the Rx coil and the 473 capacitor form a series tuned circuit?

It is untuned obviously. At Golden Mask models you can change TX freq. by simply changing C in parallel with L. Rx remains unchanged and works almost the same.
Those are working at 7,8,12,15 and 18kHz just fine with the very same RX.

[Gwil]

Again, interesting. The Rx may not be tuned to the Tx frequency but I'm pretty sure the Rx coil and C1 form a series resonant circuit. If the coil inductance was 5mH the input current would peak at a little above 10kHz.
If I've got this wrong I hope someone will explain how. (it's been a long time since I studied AC theory)

[ivconic]

Again, interesting. The Rx may not be tuned to the Tx frequency but I'm pretty sure the Rx coil and C1 form a series resonant circuit. If the coil inductance was 5mH the input current would peak at a little above 10kHz.
If I've got this wrong I hope someone will explain how. (it's been a long time since I studied AC theory)

Actually is all there in Andy Flind's "Magnum" article.
I guess you can find it here on forum somewhere.

[Gwil]

It's true that Andy Flind believed the coil was "untuned". From the original article:
　
"TR2 is the received signal preamp and is connected as a common base amplifier. This and oscillator TR1 are both based on designs which have been used in several manufactured machines because they are simple and work well. The receive coil L2 is untuned; this, coupled with the low impedance input load of TR2 ensures the predictable phase response required for reliable discrimination."
　
The fact that the Rx was based on existing designs may be significant. I'm wondering if AF saw there was no capacitor across the coil in these designs and assumed it was untuned, not realising that the capacitor connecting it to the emitter formed a series resonant circuit (note that its value is unusually small for just a coupling capacitor - its reactance at 15kHz is 226 ohms). I make its resonant frequency about 7.4kHz, compared to the Tx freq of 15kHz.
　
Of course I could be wrong but when I see an inductor and capacitor in series I see a series resonant circuit until it's shown not to be.

[Gwil]

Since the detector operates at a frequency well away from the Rx LC resonance perhaps a better approach is to see the reactance of the capacitor cancelling out some of the coil reactance, which improves the input signal (current). In that sense you could say it's "untuned".

[bandito]

PCB's have arrived, now to hunt down some parts

These boards I think are wrong

[SVEN1]

Why?
Ivonic had choice of 3 boards you can use.

I made "mag_redu_pcb" version, which is SMT (Surface Mounting Technology) or SMD (Surface Mounting Device) version.
But unlike the "mag_compl_pcb" version; here at "mag_redu_pcb" version: i used 1206 sized SMD components.
I did that for one simple reason; to be able to solder them manually.
1206 sized SMD components are just about "human" enough to be manipulated and soldered by a common hobbyists.
For those with much better sight and more calmer nerves: the fist one; the "mag_compl_pcb" version will be also alright.

[bandito]

These boards I think are wrong

Look integrated circuits are mirror,and can not be soldered,see first pin where ,,,,the layers are wrong

[SVEN1]

I don't understand what you are saying

[Toros]

Maybe the photos are mirror-reversed!

[Toros]

I don't understand what you are saying

Sven,
Look at the pictures. Each integrated circuit has marked the first leg - white point sufficiently noticeable. The photos can be seen that the point is placed on the left of the integrated circuit. But first pin is right. This means that if the photos are 1: 1 with your boards then you will have to solder chips lying on it's back and bend their legs to touch to the board.
Do you understand now?

[bandito]

I don't understand what you are saying

How will soldered,see the layout of the integral PCB and datasheet

[SVEN1]

Guess it depends upon the way you view it.