TGSL Experiments

[satdaveuk]

Repair/experiment

I repaired it, was my fault, had buggered the 2N2222A up proberly due to frying, used my old antec 25watt soldering iron which runs way to hot, I replaced both back to plastic and volla all up and going really well with stock coil.
Nice mod that one, worth doing gives that little more precision for accuracy of sine wave
Later im going to try my new coil made with .39 see what the diffrence is, Its simons experiments that prompted me with his Q factors although his experiments on his computer showed little if no advantage thought it would help to try it in real conditions.
Disadvantage right away is alot more wight at least twice more than using .25.

Anyway im really excited about this experiment and thinking positive to make a good little machine a tad better, will let you know the results soon

Regards

[Dennis the Mennis]

TGS Noise Comparisment

Hi ,

For anyone's interest and laughters :

I did some field 'experiments' under different noise circumstances with my TGS .

There are is to many info to post as attachments so I bundled all info in the PDF file



TGS noise 2.pdf



Noise source ? :






Very unpredictable noise in workshop :






Please read all in the attached PDF file.



kind regards ,

Danny

[simonbaker]

Hi ,

For anyone's interest and laughters :

I did some field 'experiments' under different noise circumstances with my TGS .

There are is to many info to post as attachments so I bundled all info in the PDF file



[ATTACH]17655[/ATTACH]



Noise source ? :


[ATTACH]17654[/ATTACH]



Very unpredictable noise in workshop :


[ATTACH]17656[/ATTACH]



Please read all in the attached PDF file.



kind regards ,

Danny

Well I gotta say excellent field work once again. I'm getting very fond of the countryside, reminds me of those old Dutch masterpieces...

Here is a question: where does that 50 hz enter the circuit? Did you try shorting or disconnecting the RX coil to see how much 50 hz stuff was left over?

At first it seems obvious that 50 hz noise should show up. But when you think about it, the noise frequency that passes through the channel should be "heterodyned" by the synchronous detector, like golfnut (I think) observed.

So really, we would expect noise at a frequency of 14.5 kHz + 50 Hz to appear as 50 Hz noise at the outputs of the LM308 -- unless the noise goes directly into the op amps after the synchronous detector. That is why it is interesting to short or disconnect the RX coil to test this. (By the way, 14.5 kHz is the 290th harmonic of 50 Hz -- eh?)

The other day I was testing noise, and I found that after shorting the RX leads before the 5.1k resistors, I can still pick up noise through the RX inputs. I then shorted the inputs of the LF353 directly (other side of the 5.1k resistors) and the noise essentially disappeared. I did not expect to see as much noise as I did when shorting the RX leads on the PCB. My jumper seemed to pick up noise, or perhaps it became part of the resonant circuit. So I'll test some more.

Anyway, thanks for the graphs DtM -- your digital scope makes a nice record of the noise that is hard to analyze with an old analog scope.

Cheers,

-SB

P.S. good overkill!

[mikebg]

Danny . . . - - - . . .
It's time to use TWIN LOOP configuration of RX coils!
Mike

[Dennis the Mennis]

Danny . . . - - - . . .
It's time to use TWIN LOOP configuration of RX coils!
Mike

Hi Mike _ ... _ _ . ,

In 'figure 8' configuration ?

btw : you should have known about 50 Hz transport of the HV net ....


kind regards ,

Danny


Dennis the Mennis

[golfnut]

mains noise

Id suspect the scale of the mains inteference is so massive its very difficult to filter away.

You MAY need some serious rejection 70, 80, 90 dB.

At these staggering high levels, The Transmit loop will be drenched in 50Hz too and will get into the syhchronous detectors etc too.

Its a tough one.

Companies like Belling lee and Schaffner make some saucy filters but are not cheap or small.

You could make some up bit like this and try on Rx side.. You would need one per input .. You would need to select the closest parts to the design.

Ideally the Tx side coil would have this too. These filters should be in a steel box with the Tx and Rx cables into one side, the filtered output on the other into ur detector cabinet. (Which should also be metal with no gaps/holes.)

[Dennis the Mennis]

Well I gotta say excellent field work once again. I'm getting very fond of the countryside, reminds me of those old Dutch masterpieces...

Here is a question: where does that 50 hz enter the circuit? Did you try shorting or disconnecting the RX coil to see how much 50 hz stuff was left over?

Hi Simon ,

In retrospective :

With the experiment near the HV lines the TGS was 'operational' ; I measured via the Rx coil.
I think the 50 Hz entered the circuit via the coil ...or at least I think so , with this kind of EMI field it could also been 'injected' direct into the pcb ...
I should have shorten the coil for experimental matters at the time , didn't think about it because I had other results in mind....

I did not disconnect the coil .

At first it seems obvious that 50 hz noise should show up. But when you think about it, the noise frequency that passes through the channel should be "heterodyned" by the synchronous detector, like golfnut (I think) observed.

So really, we would expect noise at a frequency of 14.5 kHz + 50 Hz to appear as 50 Hz noise at the outputs of the LM308 -- unless the noise goes directly into the op amps after the synchronous detector. That is why it is interesting to short or disconnect the RX coil to test this. (By the way, 14.5 kHz is the 290th harmonic of 50 Hz -- eh?)

Interesting point !
I'm planning some experiments with different coil shieldings and have some loose coils for that purpose .
I can try it in my workshop .
I can recall that the 50 Hz measured in my workshop only is measured when the coils are connected.
When Rx coil is shortened directly at the coil ( I encountered the same as you described here under : there is a big difference where you short circuit the pcb) the 50 Hz noise dissappeared .
Perhaps the noise was too small in my workshop ... I will give it a try.

On the other hand : I know for sure that there is 50 Hz in my workshop and I measured it with the spectrum analyzer , next time I'll pay extra attention in the 14- 15 KHz range ..

The other day I was testing noise, and I found that after shorting the RX leads before the 5.1k resistors, I can still pick up noise through the RX inputs. I then shorted the inputs of the LF353 directly (other side of the 5.1k resistors) and the noise essentially disappeared. I did not expect to see as much noise as I did when shorting the RX leads on the PCB. My jumper seemed to pick up noise, or perhaps it became part of the resonant circuit. So I'll test some more.

Anyway, thanks for the graphs DtM -- your digital scope makes a nice record of the noise that is hard to analyze with an old analog scope.

Cheers,

-SB

P.S. good overkill!

your welcome

kind regards ,


Danny

Dennis the Mennis

[Dennis the Mennis]

Id suspect the scale of the mains inteference is so massive its very difficult to filter away.

You MAY need some serious rejection 70, 80, 90 dB.

At these staggering high levels, The Transmit loop will be drenched in 50Hz too and will get into the syhchronous detectors etc too.

Its a tough one.

Companies like Belling lee and Schaffner make some saucy filters but are not cheap or small.

You could make some up bit like this and try on Rx side.. You would need one per input .. You would need to select the closest parts to the design.

Ideally the Tx side coil would have this too. These filters should be in a steel box with the Tx and Rx cables into one side, the filtered output on the other into ur detector cabinet. (Which should also be metal with no gaps/holes.)

Hi Steve ,


Didn't you had switch off your lcd tv to get any detection ... ?

kind regards ,

Danny

Dennis the Mennis

ryryryryryryryryryryryryryryryryryryryryryryryryry ryryry

[golfnut]

I do certainly get falses when my det is near TV .

I was getting a desciptive point out there that Unfiltered Low frequency receivers with high gain pick up all kinds of radio mush.

It wasnt a quantifiable experiment in SI units with full report


Improvements to unfiltered receivers - could come in the form of adding filters, especially if you have noise that requires filtering out.

My IGSL does not work well under power lines, perhaps I too will add a filter.

Away from power lines and and other sources of electrical noise my IGSL is OK..



Steve

[satdaveuk]

making coils with with .39

At the moment no noticable difference in real use between using that and the .25, it brought the resistance down to 16-18 ohms 5.98/6.3mh not quite the 5mh diffrence but normally does the job.
I cant remember the amount of turns because there was a long gap between making the turns and screening them up.
Will give a final opinion once ive finally potted them.
Also i need to check using .39 for rx and .25 for TX.

Regards

[simonbaker]

RX grounding, nulling, etc.

Here it is, almost the New Year, and I'm back tinkering with a basic question -- RX coil grounding, nulling, and null phase.
And already I'm somewhat flummoxed!

Let's just talk about RX coil grounding and nulling, for the TGSL coils; ignore phase for now.

We have two basic grounding configurations:

1. Ground the inverting RX lead in the coil head.

2. Don't ground the RX leads at all (see dfbowers wet-grass configuration).

Before looking at "null phase" vs. "null amplitude" in detail (a popular obsession), I thought I'd see basically how the null signal changes when you compare the two grounding configurations. Because if grounding affects the null phase, then we probably need to study both cases individually (and hopefully come up with some common theory to give us restful nights).

I couldn't remember past experiments of how the RX grounding affected the null, so I tried it again.

To start with, I'm using some unshielded coils dfbowers sent me, and I'm using a dfbowers PCB also (to keep my constructions out of the equation).

My initial tests show that grounding or not grounding the RX lead get minimum null at slightly different overlaps. A pretty small difference, but it's there. Grounded configuration requires slightly more overlap to achieve minimum null.

So why? Can someone else confirm this (remember I'm testing unshielded coils)?

I expected phase changes, but shouldn't the coils still null at the same overlap? Especially since they are not shielded.

-SB

[simonbaker]

null phase and coil grounding

I'm jumping ahead with an LTSpice simulation of the effect of RX coil grounding and its effect on the RX signal phase.

(The LTSpice sim doesn't know that my coils have minimum null at different overlaps with different grounding configurations... so I won't let on... shhhh...)

For my simulations, I just use two coils (TX and RX) and have a mutual inductance of .01.

I phase the mutual inductance coils as shown. I'm not sure yet how to justify that choice, but hopefully the results are relative anyway.

Attached is a pic of the circuits showing three different groundings and the relative phase of the waveforms as taken at the output of the op amp.

As shown, grounding affects the phase of the op amp output. I'll try to work on understanding why the sim gets these phase differences.

I'm not sure if these phases would be observed in our actual circuit; something to check.

-SB

[satdaveuk]

TX output

When time permits will disconnect TX osc and inject my coil checker osc into the TGSL because the p-p output of the TGSL is 14v and my coil tester is 24v p-p.

Its took my interest because the manufactures TGS used the third transistor as maybe a drive to up the TX output.

Anyway worth the try will let you all know results, in the meantime be good if Simon could also to tests with it on his LT spice.

Regards

[simonbaker]

When time permits will disconnect TX osc and inject my coil checker osc into the TGSL because the p-p output of the TGSL is 14v and my coil tester is 24v p-p.

Its took my interest because the manufactures TGS used the third transistor as maybe a drive to up the TX output.

Anyway worth the try will let you all know results, in the meantime be good if Simon could also to tests with it on his LT spice.

Regards

Hi satdaveuk:

If by "third transistor" you mean the JFet in the TGS oscillator, that appears to be to regulate the amplitude to keep it oscillating in the linear region and make a nice sine wave. It actually makes a smaller voltage than the TGSL.

What kind of LTSpice test are you thinking of?

Regards,

-SB

[satdaveuk]

Actually Simon since posting ive rechecked the amplitude on my TGSL and on the TX im getting just short of 20vp-p with a near perfect sinewave apart from a very small blip to the right, which is proberly nothing to worry about so by pushing that any higher do you think there would be any benefit, im proberly treading on ground you have already covered.
I think the extra 5 volts was gained when I did ivonics preset mod in the TX stage but had forgotten and had the old 14vp-p in my head, must be old age creeping on .