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Author Topic: Magnetic Delay Transformer  (Read 4127 times)

Group: Elite Experimentalist
Hero Member

Posts: 1885
Thanks again Itsu.  The dip in input power clearly shows up at 240KHz, but no OU there.  IMO it is not necessary to use a CSR for the output power, just use rms voltage squared divided by the load resistor value.  A quick check taking the Pk to Pk voltage from the screen shots doesn't improve things.  I still can't explain why the circuit losses (input power minus output power) reduce at that resonance, whereas in my mind they should increase.  Have to think more on that.


i was wondering too if i could use the output rms voltage squared divided by the load resistor value in this case, so i can.

Using that methode on the 10K load (actually measured 9880 Ohm) i get:

Freq. Vrms  Pout (mW)
200   3.14   0.99
210   3.24   1.06
220   3.33   1.12
230   3.40   1.17
240   3.45   1.19
250   3.49   1.24
260   3.51   1.24
270   3.52   1.25
280   3.52   1.25
290   3.49   1.24
300   3.46   1.21

Similar rms voltages are measured using the 100K (104.7K) equating to 100uW output range figures

let me know if i can do some more testing.

Regards Itsu
« Last Edit: 2019-11-28, 23:53:33 by Itsu »
Group: Tech Wizard
Sr. Member

Posts: 467
Hi Itsu,

Would like to ask what kind of resistors do you use for the 10 k and 100 k Loads?
I mean that their values may be different from their expected values in the 200 to 500 kHz frequency range (even if they are carbon resistors).
Even though your circuit output is surely reactive, the parasitic components of those resistors may be embedded in the circuit in an unknown way.
Somehow the resistor values should be checked at those frequencies separately from the circuit to learn about their real values.


Group: Elite Experimentalist
Hero Member

Posts: 1885

Hi Gyula,

these 10K and 100K resistors are indeed carbon ones as i do not have any high resistance inductionfree precision resistors.

So you might have a point as their parasitic components (inductive reactance) might influence the resistance in this frequency range.

Not sure however how to measure these resistors at that frequency range, but i will look for a solution.


Group: Elite Experimentalist
Hero Member

Posts: 1885
Using a known 270pF SMD capacitor parallel to the 100K (104.7K) resistor and using my picopulser to pulse
this LC (adding 8pF for my probe) i measure a damped resonance at 167MHz.

Using this resonance calculator ( http://www.1728.org/resfreq.htm  ) i calculate the inductance to
be 0.00326uH (3.26nH).  Input 167Mhz and 278pF.

This inductive reactance calculator (http://www.66pacific.com/calculators/inductive-reactance-calculator.aspx)
calculates the reactance of this 3.26nH @ 200KHz to be 0.0041 Ohms.

Guess its of no influence on the resistance.

Group: Tech Wizard
Sr. Member

Posts: 467
Okay Itsu, it sounds good enough.  I will ponder on some other simple means to check this if possible or still needed.   

The main reason I mentioned this as possibly problematic is that I find little difference in the swept voltage amplitudes between the two resistor loads in the scope shots you included in your Reply #123 (previous page). 
This small difference may come from a certain low output impedance of your circuit, very likely much lower than 10 kOhm.  So it is very likely that the 50 Ohm function generator at the circuit input transforms to the circuit output because of the 1:1 input - output turns ratio between the coupling coils and the delay circuit would not influence this significantly.  So now I think this explains why the very small amplitude difference for the two highly differing load resistance values.   

Thanks for doing these tests.


Posts: 6
Hi Itsu

Considering Gyula comments, perhaps the experiment should be repeated with a 50 Ohm output resistor.

Group: Elite Experimentalist
Hero Member

Posts: 1885

Hi Cortazar,

I did use a 100 Ohm resistor earlier, see post #121.

But using a 50 Ohm 1% induction free resistor as load parallel to the secondary LC (C again 270pF), i get
the following input / output relation (output calculated from rms voltage across the 50 Ohm (P=U²/R)):

Frequency (KHz)    input (mW)    output (mW)

    200                  56.34           46.20
    210                  56.88           46.82
    220                  57.33           47.43
    230                  57.72           48.05
    240                  58.11           48.67
    250                  58.45           49.30
    260                  58.76           49.93
    270                  59.30             "                         
    280                  59.54           50.56
    290                  59.75             "
    300                  59.95             "
    310                  60.11             "
    320                  60.28             "
    330                  60.41             "
    340                  60.53             "
    350                  60.64             "
    360                  60.67             "
    370                  60.72             "
    380                  60.75           49.93
    390                  60.74              "
    400                  60.69           49.30

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