4 quadrant VLF discrimination

[Ferric Toes]

Hi Dave,

Not related to this thread, but relevant to your last couple of sentences. The lightest weight speaker I ever saw was a helium filled party balloon made of piezofilm. The "string" contained two fine wires to the drive amplifier on a desk, and the sound was true omnidirectional and point source. Must be something about it that didn't make practical sense.

Ferric.

[Sergey_P]

Making a clipping window phase - you cut a small gold.
Need to focus on conductivity, and not on the phase

[Davor]

No, but quite near it. A quality notch at sea water vector would lower the gold amplitude by a little bit, but will also increase contrast for small gold. So it is lose a little, win a great deal.
In VLF you can apply such a sharp notch with little effort, and it can be very precise. Such notch is always present with PI rigs, and not that sharp at all. To make it sharper you have to sample very early, but there are limits. So far PIs were sold by pretence they work well on the beaches, and the nasty bit about inability to sniff small gold is usually not voiced as loud. I think this application of notch in VLF will work better than PI on the beaches.

The slope of the notch filter for phase Veratore, determined slope GEB ( cos(x) ). A method of reducing the window of phase I suggested in the topic http://md4u.ru/viewtopic.php?f=77&t=5497

You may improve slope by applying some compression too. OK, it is level determined, but as accurate as any weighting function. I applied time-accurate compression in IGSL of mine and it's phases are immaculate from closest proximity to the reception limit. IMHO with the wild variation of signal levels, a precision weighting is a bit of an overkill.

[golfnut]

Doesnt the Gold response live in the thundering great Null though!

S

[Sergey_P]

The slope of the notch filter for phase Veratore, determined slope GEB ( cos(x) ). A method of reducing the window of phase I suggested in the topic http://md4u.ru/viewtopic.php?f=77&t=5497

[Davor]

In my analysis of Verator rig I concluded that the signal produced by the X path is the one with left and right lobes since it is switched in phase with Tx, and that would produce a nice pair of holes at the sea water vector. So in any case and regardless of the differential coil it would outperform nowadays VLF detectors on the beaches. Even more so with the differential coil. The "No Signal" part of the mask I indicated as white in order to emphasize that I'll use it in a 4-quadrant solution.

Otherwise we are on the same track. However complex to follow, a Verator design is a very nice and unique rig.

[Sergey_P]

[Davor]

Ah, I just noticed that I've put R and X coordinates wrong ... anyway, you got some idea what I wanted to say.

[Davor]

So, you can observe the channel that produces a tone as a masking function - it masks ground signal. In classic solutions it masks ferrite-like responses, in Verator it primarily masks high R responses like those of the sea water and additionally it punches a hole in ferrite-like response angle to make it just perfect. Verator does that by means of a VCA (2-quadrant multiplier) produced as a PWM controlled switched capacitor attenuator (phew!).

What I want to achieve is a tone response mask as a separate function from phase discrimination vectors. Thus I'd have ground responses at bay regardless of my discrimination settings. It means that my Fe and Cu tones may overlap, but the sea water response will be attenuated anyway. A perfect beach analyser! With 4-quadrant discriminator and a differential coil it will eat the existing PI toys on their own terrain.

The mask I'm talking about is a clover-like with 4 deep holes fixed at ferrites and sea water. Discrimination vectors may be set freely and independently (red and green).

To obtain that clover-like mask I'll need a real analogue multiplier. It is produced by multiplication of two channels at angle.

Of course, patent trolls go to hell!

[Davor]

If I got it right, and I'm sure Sergey will correct me if I'm wrong, his Verator uses the following tone extraction scheme which uses a Disc signal (the lobes) and punches an additional hole in the left lobe (dashed line) for suppression of the reactive ground signal. IMHO just brilliant! It makes Verator a perfect rig for beach combing.

[Davor]

The paper is interesting, and has all the math behind it. It can be implemented by Tayloe-like switches and weighting resistors, I even saw such implementation in one zero-IF Rx. However, for signal extraction I'd prefer a classic lock in amplifier because of complexity difference.

What I need here is a real analogue multiplier. I wish to separate phase detection from detection amplitude because of a distinctive advantage: ground balance for both resistive and reactive components - all the time.

I'll give an overview of what I want in a few posts to make it easier to follow. First is the "classic" VLF constellation, without the discrimination angles, say an "all metal" response. It is typically used for target response level. In 2-quadrant Rx only the greenish lobe is used:

[Aziz]

http://jre.cplire.ru/win/sep07/2/text.html

Hi Sergey, unfortunately, we don't speak Russian.

http://www.microsofttranslator.com/bv.aspx?from=ru&to=en&a=http://jre.cplire.ru/win/sep07/2/text.html

(The translation isn't optimal but better than nothing.)
Aziz

[Sergey_P]

a 4-quadrant analog multiplication

http://jre.cplire.ru/win/sep07/2/text.html

[Dave J.]

George Payne patented a 4-quadrant analog multiplication motion discrimination scheme in the late 1970's. I don't remember what he used for the multiplier. In the distant past I've configured LM13700's as analog multipliers, with offset adjustments of course. In principle the limited dynamic range of analog multiplier circuits could be overcome with an AGC system but I haven't seen it done.

When it comes to analog computation, there are lots of schemes besides the ones in textbooks. Back in the 1970's I designed a circuit which took anemometer reed switch pulses and used that to compute the integral of the root mean cube windspeed, which is equivalent to wind energy. It wasn't even very complex (of course no microprocessor), but unlike most of my designs it was darn clever.

* * * * * * *

In my opinion you're trying to solve a problem that doesn't need to be solved. However if you're a hobbyist rather than a commercial engineer, that may not be relevant. I have my day job where what I do is supposed to make practical sense, but I also have hobby projects that intrigue me even though someone else would say they don't make any practical sense.

My favorite hobby project these days is to see how much medium-fidelity sound I can get out of a compact light weight speaker system that runs for darn near forever on a couple of AA cells. It's been a good education on speaker acoustical design, and what I've learned by actually doing goes against a lot of conventional practice.

--Dave J.

[Davor]

A small update...

I became aware of some unique solutions that happen in Verator rig that make the quest for a real 4 quadrant rig even more important. Thanks Sergey. The very special thing that happens in Verator is that instead of a GEB, i.e. an all metal channel, it uses a Disc. channel for extracting audio. With no intentions to go into a deep analysis, this means that Verator is capable of detecting happily in salt water environment (hooray!). It also quiets the reactive response, i.e. ferrite response ... the GEB null, by multiplying the previously mentioned signal with GEB using a two quadrant multiplier. That's just brilliant!

So, for my 4-quadrant Rx I wish a dedicated audio producing channel that has holes at salt water and at ferrites phases, so that neither produce any tone in my rig. That plus a differential coil would give me a considerable edge over the existing PI rigs, and discrimination too.

The only thing I'm missing is a proper analogue multiplier. I have some ideas about that too.