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Author Topic: Itsu's workbench / placeholder.  (Read 2622 times)

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Still trying to match the 50 Ohm Tracking Generator to the toroid under test for maximum power transfer.
I went back to the 174nH which at 45Mhz stands for a reactance of 50 Ohm.
This 174nH is accomplished by having a 4 turns coil around the T225-6 toroid.

For tuning i put a 100pF trimmer cap in series with the coil and that seems to work allhough
the tuning peak is very broad.

What i do notice on the Spectrum Analyzer screen is not only this broad peak manifesting itself
by moving the whole screen line up or down, but also a smaller peak which does not move, not
by the trimmer adjustment, nor by touching the coil, toroid or trimmer.

I use the TG/SA in series mode, see here:
http://www.overunityresearch.com/index.php?topic=3691.msg71352#msg71352


Screenshot shows the little peak, a video is here:
https://www.youtube.com/watch?v=pWU2wYwUFTE


Itsu
   

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...but also a smaller peak which does not move, not by the trimmer adjustment, nor by touching the coil, toroid or trimmer.
1) What if you slightly change the number of turns or the length of the BNC cable ?
2) What if you connect the two BNC cables (with screw terminal adapters) directly with two bolts (effectively making a "through"), thus taking the coil and trimmer out of the measurement alltogether?

P.S.
After doing pt.2 it would be prudent to calibrate / normalize the SA. Next, reinsert the trimmer and repeat the measurements and then reinsert the coil and do the measurements again.
   

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1) What if you slightly change the number of turns or the length of the BNC cable ?
2) What if you connect the two BNC cables (with screw terminal adapters) directly with two bolts (effectively making a "through"), thus taking the coil and trimmer out of the measurement alltogether?

P.S.
After doing pt.2 it would be prudent to calibrate / normalize the SA. Next, reinsert the trimmer and repeat the measurements and then reinsert the coil and do the measurements again.

If i replace the coil/cap by a BNC-BNC through, the peak stays.
When normalizing with this through, its gone of cource, but it stays gone when reinserting the coil/cap.

So it is an artifact of the normalisation process which i did by placing a "short" across the coil/cap.
This short (piece of 5cm copper wire) parallel to the coil/cap seems to create this little peak.

Thanks Itsu
   

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You should always normalize after completing your cabling and test fixture and immediately BEFORE inserting the DUT. Otherwise you'll be measuring the fixture, too.
   

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Yes, and i do, but the normalizing was done with a short jumper cable across the (series mode attached) dut
(the grounded testleads are fixed connected by a jumper).
So a had 2 short jumper cables shorting the dut during the normalizing, but still this causes the peak at 43Mhz.

Well, good to know, again.

But it shows that this 4 turn coils with 100pF cap can make a good match to the TG/SA.

Itsu

   
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...
This short (piece of 5cm copper wire) parallel to the coil/cap seems to create this little peak.
...

Maybe it acts as an antenna and you receive a transmitter in the neighbourhood? The scope itself, or a generator, or any other electronic equipment nearby may have clocks generating such signals.
Could you listen to the frequency with a radio?


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No, no sign of any big signal around 43Mhz.
I do see he local 105Mhz FM station on the SA, but thats way more broadbanded.

Also the SDR receiver only shows some minor crap signals around 43Mhz, nothing strong.

Must come from the coil/cap i guess during the (wrong) normalisation process.
   
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Also the SDR receiver only shows some minor crap signals around 43Mhz, nothing strong.

Must come from the coil/cap i guess during the (wrong) normalisation process.

A resonance effect in the internal circuit of the scope must not be eliminated, as well as a signal generated by the scope itself but weak and undetectable from the outside. If you connect the SDR in place of the scope, does it also show the peak? If so, it becomes very interesting.


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I am not using a scope,  just my Spectrum Analyzer with its Tracking Generator.

The 43 / 41Mhz dip/peak is caused by the normalisation process i do before any test.
It seems that using a short piece of wire (5 - 15 cm) to short out the DUT creates this 41/43Mhz dip
which then after normalisation and removal of the shorting wire turns into a (false) peak.

See video here:   https://www.youtube.com/watch?v=6iis2eHjJNU

Itsu
   

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The problem with my nanopulser as shown a few posts ago here:

http://www.overunityresearch.com/index.php?topic=3691.msg71665#msg71665

is that the Pulse Repetition Frequency (PRF) was to high (min. 1Khz) as we now need a PRF of about 1Hz.

The nanopulse drive circuit (74HCT00 and 74HCT02) used was not able to go that low, so verpies designed
a new drive circuit around a single 74HC221 chip, see diagram.

This drive circuit is able to generate a 100-200ns square pulse at about 5V every 1Hz which is OK to drive
the nanopulse circuit.

I breadboarded this new circuit and was able to produce these 100-200ns pulses at about 2Hz PRF.
A quick and dirty test using the nanopulse circuit showed good result, see screenshot.

I also made a LTspice simulation of this drive circuit, see picture below which shows in green the 85ns square pulse
from pin 5 going to the R7 load and in blue the output from the oscillator stage at pin 13.
.asc file attached. (make sure you have the 74HC library).

I now need to build this drive circuit the proper way (RF sound) to get it running stable.


Itsu
« Last Edit: 2019-02-03, 14:22:21 by Itsu »
   

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It's not as complicated as it may seem...

I am not using a scope,  just my Spectrum Analyzer with its Tracking Generator.

The 43 / 41Mhz dip/peak is caused by the normalisation process i do before any test.
It seems that using a short piece of wire (5 - 15 cm) to short out the DUT creates this 41/43Mhz dip
which then after normalisation and removal of the shorting wire turns into a (false) peak.

See video here:   https://www.youtube.com/watch?v=6iis2eHjJNU

Itsu
Itsu,

It would be interesting to see a normalization sweep using a 6" piece of 50R coax with 50R N-N or BNC-BNC connectors.


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Itsu,

It would be interesting to see a normalization sweep using a 6" piece of 50R coax with 50R N-N or BNC-BNC connectors.

Poynt,     you mean parallel to the DUT like i did in the video using a 6" piece of copper wire?

I know when removing the DUT during normalisation (which is how it should be) and using a bnc to bnc connection across the TG/SA the 43Mhz dip/peak is gone.


itsu
   

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It's not as complicated as it may seem...
I did mean direct, not in parallel with the DUT.

Interesting that adding the wire in parallel had that effect. But then again, we know that a wire is not just a wire.


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The new nanopulser driver simulation as shown above in post #159 was expanded with the pulse generator components
as i have it running (with some changes as i could not find the correct LTspice components).

The picture shows the complete circuit with the result.

light blue is the MOSFET driver input (from the 74HC221)
green is the MOSFET driver output / gate signal
dark blue is the MOSFET drain signal
red is the nanopulse across R8 ( probe referenced across R8)


Remarks;

for MOSFET driver i use the UCC27511 instead of the shown LTC4440-5 running on 12V instead of 20V here.
The nanopulse diode D4 is a KD226D in my circuit instead of the MUR460 here.
The generated nanopulse (red) is not really the real nanopulse as the MUR460 is not a good diode for it,
nor probably LTspice can simulate it.
Also the used toroid transformer in the pulse part probably needs to be saturated which is not attempted here.
Toroid is a 10x6x4 one with 6 turns primary and 12 turns secondary.

Itsu
   

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The generated nanopulse (red) is not really the real nanopulse as the MUR460 is not a good diode for it,
nor probably LTspice can simulate it.
Yes, I don't think LTSpice can simulate the DSR effect in diodes, which is essential for the generation of the nanopulse.

Also the used toroid transformer in the pulse part probably needs to be saturated which is not attempted here.
The saturation of the transformer's core when the voltage across C7 reaches its peak is very important for the amplitude of the nanopulse.


ANOTHER OBSERVATION:
If the diode D3 is a bidirectional TVS diode (or a Transil, Transorb) then the current in the primary winding of the transformer is interrupted much faster than with a regular or Schottky diode.
The main required characteristic of such bi-dir TVS diode is that its clamping voltage (VTVS) is greater than the Drain supply voltage (V3) and LESS than but close to the maximum Drain-Source voltage (VDS_MAX) of the power MOSFET minus V3.  In mathspeak: V3 < VTVS ≤ (VDS_MAX - V3)
   

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Hmmm,  the TVS diode would be a problem then in my real circuit as V3 is 130V and Vds=200V (IRFP260N).
   

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Hmmm,  the TVS diode would be a problem then in my real circuit as V3 is 130V and Vds=200V (IRFP260N).
Yes.. and that explains why a normal diode sits in there.

For such low VDS_MAX MOSFETs a TVS diode can do its job in this D3 position.
...and what this position changes is that now the TVS diode has to have a clamping voltage greater than V3 and LESS than VDS_MAX (but close to it) and it does not have to be bidirectional.  In mathspeak: V3 < VTVS ≤ VDS_MAX

I recommend checking with a scope whether the TVS diode is really clamping at the declared voltage with the target pulse width, because I found out the hard way, that the datasheets are not always truthful about this parameter.
« Last Edit: 2019-02-05, 19:20:27 by verpies »
   

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Thanks,  i prefer to keep the good old nanopulser part the way it is as it seems to work rather reliable now.

I can make another DSRD section using say a FQA11N90 (900V) MOSFET so i can double the drain voltage to 260V
and still use your bidirectional TVS diode scheme (900-260=640V).

Goes to the todo list.

Itsu 
   

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Of course.

When you will be building a new DSRD Section, consider the transformer core selection tips in the attached article.
   
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Interesting article, impressive peak power.
It reminds me of the discussion thread DSRD pulse generator on the subject we had a few years ago.


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I build the verpies designed 74HC221 nanopulse driver on a pcb in "dead bug" fashion and boxed it in
a small tin box so to exclude as much noise as possible.

Video here: https://www.youtube.com/watch?v=L4_3zEOky_g


Itsu
   

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Peppermunt, huh?
Seems pretty crisp to me....
What is the adjustment range ?
   

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Yep, "pepermunt", they came in these neat tin boxes, however, not anymore,  my wife took another brand, plastic now.

I did not check the range yet, but will be enough to cover my needs i think.

I added a 50 Ohm series resistor at the output pin 5 (to coax) to minimize the reflections like we did on the TL494.
But it did not do much, guess its crisp enough.


Itsu 
   

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I added a 50 Ohm series resistor at the output pin 5 (to coax) to minimize the reflections like we did on the TL494.
But it did not do much, guess its crisp enough.
To minimize the reflections, the series resistor PLUS the internal output impedance of the 74HC221, together would have to make up 50Ω.
The internal coax would have to have the 50Ω impedance, as well.  The connector through the peppermunt's wall, too (e.g. a BNC female panel connector).

However, the MOSFET driver, that will be fed by these ~100ns pulses in the future, does not have a 50Ω input impedance, so a different match would have to be done with it.
« Last Edit: 2019-02-09, 19:16:29 by verpies »
   

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a little update,   as i got some parts like the bidirectional TVS diode (1.5kE440CA), some P600M diodes,
some TN10/6/4-3E25 (white) toroids.

The TVS clamps at 450V, (using a flyswatter at 1200v), so fairly close to its specs.

I made a 200V drain power supply out of the flyswatter  :D! and tried this setup (74HC221 driver, 200V flyswatter PS)
with my old nanopulser part and it reached 1.5KV.

The flyswatter PS (output 1200V @ 3V input) has a 440TVS across its output clamping it to 450V, followed by a
200V zener into a 330uF / 450V capacitor and is able to keep the voltage (200V) stable at the 1Hz pulse repetition
frequency.

Any problems to be foreseen with this 200V setup?
Its very tiny, does the job and as said has enough energy stored into the cap to keep it pulsing, as a matter
of fact, it keeps on pulsing about a minute after removing the input to this cap, slowly dropping the nanopulse
amplitude.

Regards Itsu
   
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