field test unit no 001 "model T"

[Aziz]

Yes, that's what I would expect to see.

D'accord.
But very difficult to make it visible in a simple excel table. You know, the disbelieving guys here wouldn't believe me, that it is a high-pass filter in the interesting (low) frequency region.

I'm now making an appeal to the guys to show the integrated window subtraction method, which usually occurs in a PI technology. This hasn't been proved (or showed) yet.

But I'm not very keen on to bite the bullet this time. (Ok, I admit, that it's beyond my scope. Honestly, no kidding .) Who wants be a hero? Sido?
(Or PJ? UFox? Robby_H? Rafferty? Lord Fatcat? Anyone else? )
(BTW, one can make use of the math symmetry to make the proof simple. Just focus to the worst case condition in the low frequency region.)
Good luck. I believe in you guys.

Aziz

[Carl-NC]

Look at this transfer characteristics (red):

http://www.musicanddesign.com/images/DW_eq4a.GIF

(not to scale with our table)

Yes, that's what I would expect to see.

[sido]

I will........Aziz....what you mean is aaaaaadddd the intergrals

[Tinkerer]

Correct. Too much reliance in the past on the simple mono coil, because of its simplicity, where the constraints are for the benefit of the TX.

Eric.

I am going to start a new thread with this, so as not to highjack this thread.
Lets look at some alternatives to the simple mono coil configuration.
Separate TX-RX of same or different amount of turns and inductance.
IB configurations, concentric and not. Different amount of turns or different inductance.
Differential coils
etc.

Tinkerer

[Aziz]

Hey we aren't finished.

Anyone want to try the subtraction of integrals and wanna see the transfer function? This is more complex and difficult to do it as you have to calculate the differences of integrals this time.

Who is going to bite the bullet this time?
Aziz

[Ferric Toes]

But then again, you just identified a next optimisation path - PI Rx inductance is far below the optimal for noise performance of nowadays preamps. Rx inductance may be observed as an auto-transformer having a primary inductance of a Tx coil. So the achieved Rx voltage will be increased by a square root of the Rx/Tx inductance ratio.

Correct. Too much reliance in the past on the simple mono coil, because of its simplicity, where the constraints are for the benefit of the TX.

Eric.

[Davor]

Inductive or capacitive reactance does not generate noise. In the case of a coil, the thermal noise contribution is only that of the dc resistance. At the present state of the art, noise sources in the preamp will far outway the noise of PI coils which vary between 0.5 and 5 ohms dc resistance.

Yes, I checked for the typical values of PI inductances and you are right. There is no way with nowadays preamps to ever come close to such low source resistance. The effect I was referring to is noticeable with several mH coils in IB systems where in effect some impedance transformation happens.

But then again, you just identified a next optimisation path - PI Rx inductance is far below the optimal for noise performance of nowadays preamps. Rx inductance may be observed as an auto-transformer having a primary inductance of a Tx coil. So the achieved Rx voltage will be increased by a square root of the Rx/Tx inductance ratio.

[Ferric Toes]

It is safe to assume that such coupling would improve Rx processing by removing EF prior to sampling. It would not affect the preamp offset though. The offsets can be tackled with a later sample, but also with some clever servo to fix the offset problem at the preamp.

Beside the DC blocking, series capacitors are useful in lowering the effective coil Z over a large frequency range, which in turn improves the input noise. The final frontier is limited by a coil wire thickness (surprise!).

Inductive or capacitive reactance does not generate noise. In the case of a coil, the thermal noise contribution is only that of the dc resistance. At the present state of the art, noise sources in the preamp will far outway the noise of PI coils which vary between 0.5 and 5 ohms dc resistance.

The dual sampling and subtraction method is very good at removing EF signals, and personally I do not see any reason to change it. Properly designed with optimal sample spacing, depending what type of targets you are looking for, it is effective at minimising power line frequencies too. Again, properly designed, there are no response holes in the basic two sample method. If greater attenuation is required you can, with a feedback circuit, make the front end have a bandpass response that rolls off at the LF end just short of the TX pulse rate. This can also double as an offset servo.

Eric.

[Aziz]

Ok guys,

don't pick on UFox anymore. I think, he has learned something. I hope, that PJ did learn something too.

Yup, I've learned either.
Aziz

[moodz]

OK, beside UF and whatever issues you pursue, there might be some honest people that expect some higher meaning to this discussion. Well, there is none. You don't have to go for Fourier to learn about what a DC blocking capacitor does - Bode plots are just as revealing. Unlike FFT that loses phase information, a Bode plot teaches us that a phase is affected one decade above and below the -3dB cut-off frequency. Now imagine a 10Hz cut-off. For every signal that is above 100Hz (one decade up) there is no amplitude or phase shift to affect anything.

It is safe to assume that such coupling would improve Rx processing by removing EF prior to sampling. It would not affect the preamp offset though. The offsets can be tackled with a later sample, but also with some clever servo to fix the offset problem at the preamp.

Beside the DC blocking, series capacitors are useful in lowering the effective coil Z over a large frequency range, which in turn improves the input noise. The final frontier is limited by a coil wire thickness (surprise!).

very true ... but with an ideal capacitor and an infinite input impedance there will be no ( practical ) corner frequency because the impedance of the capacitor is irrelevant in comparison to the infinite input impedance of say an amplifier. So if you know what frequencies you want to pass across a capacitive coupling its simply a matter of making sure that the capacitor impedance << input impedance at the frequencies of interest ( thats a rule of thumb for people who dont make or calculate exact filters ).

For UF ... signals dont enter and leave capacitors ... they are just like resistors ( frequency sensitive ones ) for AC signals with ***WOW*** "reactance" ***WOW***.





.

[Davor]

OK, beside UF and whatever issues you pursue, there might be some honest people that expect some higher meaning to this discussion. Well, there is none. You don't have to go for Fourier to learn about what a DC blocking capacitor does - Bode plots are just as revealing. Unlike FFT that loses phase information, a Bode plot teaches us that a phase is affected one decade above and below the -3dB cut-off frequency. Now imagine a 10Hz cut-off. For every signal that is above 100Hz (one decade up) there is no amplitude or phase shift to affect anything.

It is safe to assume that such coupling would improve Rx processing by removing EF prior to sampling. It would not affect the preamp offset though. The offsets can be tackled with a later sample, but also with some clever servo to fix the offset problem at the preamp.

Beside the DC blocking, series capacitors are useful in lowering the effective coil Z over a large frequency range, which in turn improves the input noise. The final frontier is limited by a coil wire thickness (surprise!).

[UrbanFox]

Fox, I edited your prior post to remove the name calling. Keep it up and you'll be banished to Doug's forum.

Fair enough, Carl.

I think you've overstepped your understanding of signals regarding DC content.

Carl, i am just wanting to present that a non-sinusoidal waveform doesn't necessarily exit of a capacitor looking the same as it did when it went in. Multiple frequency signals, such as broadband signals, behave differently because capacitive reactance is frequency dependant. Also of some possible relevance, an AC coupled square wave will rise and fall when the duty cycle is varied.

[Aziz]

Fine. UFox is learning now. (I appreciate this. )

[Aziz]

A comb filter is what I was thinking of. Aziz, I think you will see this if you did a more detailed selection of frequencies.

Ok, I have found a transfer characteristics, which is exactly describing what you thought of and it's the more correct version of course, if we look more detailed at higher frequencies.
(I have cheated a bit outside the worst case scenario )

Look at this transfer characteristics (red):

http://www.musicanddesign.com/images/DW_eq4a.GIF

(not to scale with our table)

And you can see, when I begin to simplify (the cheat):
SubtractionMethodAttenuation.zip

But the high frequency region isn't much relevant for the EFE effect and low frequency cancellation. The low frequency transfer characteristics is much more interesting to show.


Someone could look at the subtraction of integrals now.

Cheers,
Aziz

[Carl-NC]

Fox, I edited your prior post to remove the name calling. Keep it up and you'll be banished to Doug's forum.

I think you've overstepped your understanding of signals regarding DC content. You won't win on this one when you're that wrong. Read up on Fourier Series.