Field Strength Measurement with the MDF antenna?

Aaronia Antennas (HyperLOG [logper], BicoLOG [biconical], OmniLOG [isotropic/3D], MagnoTRACKER [magnetic] and our EMC/EMI-Probe-Set)

Field Strength Measurement with the MDF antenna?

Postby Moderator » Friday 13. March 2015, 08:04

I am using the new MDF antenna and want to make field strength measurements of the magnetic field without using the MCS software.
Which setups do i need in the SPECTRAN 60100 V4 ?

For the passive MDF antennas (without preamp) you need no changes at all (MDF560 and MDF9400):
The dBm reading of the SPECTRAN now are dBA/m including correct sign so if the SPECTRAN would show -70dBm you have -70dBA/m.

For the ACTIVE MDF antennas (with attached preamp) you only need to set the preamp gain in the "RefOff" menu.
Set it to +35dB for the MDF930X (1MHz - 25MHz with max. +/- 0,5dB deviation)
Set it to +25dB for the MDF960X (1MHz - 40MHz with max. +/- 1,0dB deviation)
Set it to +40dB for the MDF50400X (1MHz - 40MHz with max. +/- 1,0dB deviation)

Please note that if you operate the MDF antennas outside the recomended[b] measuerement frequency range the deviation will get higher (see data sheet curves).[/b]

And for all Excell fans attached the conversions for dBA/m (dBm) to Tesla or Gauss:

    dBm = dBA/m (This conversion is valid for the MDF560 and MDF9400 antennas only!)
    A/m = 10^((dBA/m)/20))
    µT = (A/m)/0,7958
    nT = (µT)*1000
    dBpT = 20*LOG((µT)*1000000
    Note:
    1 Tesla = 10000 Gauss

    dBm-25 = dBA/m (This conversion is valid for the MDF960X antenna only!)
    A/m = 10^((dBA/m)/20))
    µT = (A/m)/0,7958
    nT = (µT)*1000
    dBpT = 20*LOG((µT)*1000000
    Note:
    1 Tesla = 10000 Gauss

    dBm-35 = dBA/m (This conversion is valid for the MDF930X antenna only!)
    A/m = 10^((dBA/m)/20))
    µT = (A/m)/0,7958
    nT = (µT)*1000
    dBpT = 20*LOG((µT)*1000000
    Note:
    1 Tesla = 10000 Gauss

    dBm-40 = dBA/m (This conversion is valid for the MDF50400X antenna only!)
    A/m = 10^((dBA/m)/20))
    µT = (A/m)/0,7958
    nT = (µT)*1000
    dBpT = 20*LOG((µT)*1000000
    Note:
    1 Tesla = 10000 Gauss
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Re: Field Strength Measurement with the MDF antenna?

Postby Bernard » Friday 18. March 2016, 15:13

Measuring the field far from the transmitting station (plane wave : E/H=377 Ohm), 0dBA/m (i.e 1,25µT) is accompanied by an electric field 53,5 dBµV/m, it means a power flux E.H = -62 dBm/m2. If the receiving antenna delivers 0dBm on its connector, it means, its equivalent area is 1,7 million square meters and its gain +51,7 dBi… It is impossible. Where did I make the error ?
Bernard
 
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Joined: Friday 18. March 2016, 08:37

Re: Field Strength Measurement with the MDF antenna?

Postby Moderator » Friday 18. March 2016, 19:11

This is a MAGNETIC antenna, with high e-field suppression so you cant calculate electric fields with it.
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Re: Field Strength Measurement with the MDF antenna?

Postby Bernard » Sunday 20. March 2016, 08:47

Of course it is a magnetic antenna, but in Fraunhoffer area, it means far from a transmitting antenna, wave's magnetic field and electric field are in the ratio Z = 377 Ohm (Z is the product of vacuum permeability µ0=4π10-7 by the wave's speed c=3*10^8) that results directly from Maxwell's equations in case of plane wave. Then, in this case, the measurement of H makes able to calculate the electric field E (just in multiplying by Z). I can express my question otherwise : "the power flux of an electromagnetic wave in Fraunhoffer area is 377*H^H, because E (what is not measured by the antenna, I agree) is equal to 377H. With the value of 0dBm received power in 1,25µT magnetic field, the equivalent area of this antenna (what is the ratio received power / flux ) is more than 1 million square meters, that is impossible." Sure, I'm wrong, but where ? Would not it be a confusion between magnetic field and magnetic induction ? between H and B ?
Bernard
 
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Re: Field Strength Measurement with the MDF antenna?

Postby Moderator » Sunday 20. March 2016, 08:55

Simple error: This formula only works in the RF frequency range....
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Re: Field Strength Measurement with the MDF antenna?

Postby Bernard » Tuesday 22. March 2016, 08:53

Certainly it works in the RF frequency range AND with established wave propagation, i.e. in the Fraunhofer area of transmitting antenna, what begins about at four wavelengths from this Tx antenna.
Rx antenna MDF 9400 works up to 400 MHz. So at 25 MHz and more than 48 m far from the Tx antenna, we are clearly in the RF frequency range . At such a point, the magnetic field, what is measured by this magnetic Rx antenna, is perpendicular to an electric field, what is not measured. And Maxwell's equations shows that power radiated flux must be Z*H^H where Z=µ0c=377 Ohms. If the power delivered by Rx antenna is 1mW (0dBm) for 1,25µT, it means an impossibly gigantic equivalent area for this antenna. Power flux is 1,25.10-6*1,25.10-6*377=5,89.10-10W/m2=-62,3dBm, what is a very low flux to induce 1mW in the Rx antenna.
I suspect there is somewhere a confusion between B and H in applying Maxwell's equation for plane wave (E/H=µ0c). Don't you ? Thank you for helping : I need to calibrate the antenna in order to answer the question "in a free space plane wave, where the ratio between E and H is 377 Ohms, if I measure n dBm with this magnetic antenna, what would I measure, in dBm with a half wave dipole electric antenna ?"
Bernard
 
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Joined: Friday 18. March 2016, 08:37

Re: Field Strength Measurement with the MDF antenna?

Postby Moderator » Tuesday 22. March 2016, 18:28

AGAIN: This is a MAGNETIC antenna, with high e-field suppression so you cant calculate electric fields with it.

I will now close this thread.
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