coil induced voltage measuring

Hello,

I am trying to conduct an experiment involving a loop antenna and a small coil of conductor. I have the the antenna producing a 10MHz sine signal.

I would like to put a remote coil (with no power source of its own) at varying distances from the antenna and record the voltage induced on the coil itself (due to the magnetic field of the loop antenna).

I have tried measuring the voltage across the coil terminals with an oscilloscope probe and I do get some readings.

However, if i just put the oscilloscope probe next to the antenna by itself there is also an induced voltage, with no coil attached.

How can I accurately measure the induced voltage on the coil with an oscilloscope or are there other methods available?


Please, can someone advise me on how to go about this experiment


Thanks for your time

Hi

I have some experience in such measurement but using spec analyzer

I think your probe is good antenna self.

Try 50Ohm input of oscilloscope with 50Ohm cable connected
I seen, that cable (with open end or shorted) has not received valuable signal,
and, when loop was connected to cable, the signal was received with valuable value.

Regards

The oscilloscpe probe i have has a 1 Mega ohm impedance for 1X and 10 Mega ohm settingfor 10 X. Is that ok?

Should I use 1X or 10X in this experiment ?

In fact, would a spectrum analyser be more suitable?

Hi
I think so
The problem is not impedance,
the problem is probe. I seen that variouse probes dont reject common mode proper. The surface of probe is antenna by the definition, and (possible to say) induced voltage on surface is transformed by probe to diff voltage.
Such problem can exist with cable too, due to poor EM shielding for ex.

Connect cable to osc or analyzer short ends and connect your finger to shorted ends If You see valuable signal than this cable or probe is not so good. It transfoms loop voltage---device ground - cable shield - your finger - your body to device ground capacitance---to device input diff voltage. So You have relatively big loop with out any external wire loop. Try another cable or probe in this case

Regards
Glad to help

The solution could be a dual channel oscilloscope in differential signal configuration.
Common signals should be canceled (if the probes in both channel are identical) but the signal from the coil should be displayed.

(This could be a solution in low frequency range, I am not sure if it will be effective at 10 MHz ).

I'm still having problems, It seems the probes I have are not too good and trying the dual channel solution is just adding more headaches unfortunately.

Would it be any better if I connected the probe ends to 2 very long wires and then connected the other end of the wires to the coils terminals? Or is this simply just making matters worse ?

There must be a way around this, it seems like a standard type of test. Has anyone performed this type of test themselves?

Added after 9 minutes:

Is it simply a case of measuring th voltage induced with the probe by itself (left open or short?), then measuring the voltage induced with the probe connected to the coil and taking the difference between the 2 values?

Sorry for all these questions, I really would like to know.


Regards

In using a coil, you may be making the coil too small, the impedence across the coil is too small at the frequency/wavelength that you are trying to measure - the larger the diameter, the more singnal you will pick up. Remember that an antenna becomes more efficient as the length approaches 1/4 wavelength.

A side from that, I have made relative field strength measurements using a scope probe with a length of straight wire (4 to 6 inches) connected to the probe tip and the probe ground left unconnected.

I would suggest that if you are interested in antena design/RF measurements that you might check out the "ARRL Antenna Book," published by the American Radio Relay League. You may be able to get a copy at your local library

Regards,
Rick

Why must the probe ground be left disconnected (floating) in this case?

How reliable would the two probe diferential setup be at high frequencies? Has anyone got any expereince with this?


Kind Regards :)


Cat

can you calibrate? an o-scope? if so do this.

use the shorteset wire length of probe possible. move the probe as far away from the source as posible and of course a shieled wire should help.

other than that dont know