Hi Raphael,

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I wouldn't read too much into the webpage copyright statement, I used to have something similar, especially after a few companies copied some of my work and built businesses around it.

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Rather disappointingly, they were based in the USA, so I don't think IPR theft is constrained by geography.

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Unfortunately, folks tend to ignore such statements, and it's only when a legal case is pursued that they have any real validity. If you can afford to defend your IPR that's fine, but in most cases it's not worth the financial risk.

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Bottom line, if you don't want your IPR to be infringed, simply don't release it into the public domain.

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Regards,

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Martin

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On Thu, Oct 3, 2024 at 03:51 AM, Raphael Wasserman wrote:

On Wed, Oct 2, 2024 at 08:51 PM, Raphael Wasserman wrote:

Also, our discussions are applied to a magnetic loop antenna only. For more complicated case, a loop antenna may pickup electrical field which complicates the layout of equivalent circuit since we must be include as well as another voltage source with a capacitive coupling like for monopole whip antenna.

Antenna theory doesn't really separate E and M fields. The combined response of the antenna is a function of both, meaning that there is no such thing as "magnetic loop". You are correct that in the case of a very small antenna it is usually a function of one of the components.

The E field causes a common mode voltage on both small loop terminals, referenced to the amplifier ground. Combined with the amplifier common mode response, it may affect the loop+amp system parameters. For example, the null depth above 7-10MHz is not good for a 1m loop and a simple preamp like M0AYF.

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My opinion is that a dummy loop equivalent for testing preamps should include a circuit to apply common mode voltage.

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73, Mike AF7KR

Agreed - "Magnetic Loop" is shorthand for current derived signal, E-Probe / Active whip or Dipole, is shorthand for voltage derived signal.

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But in practice they contain a bit of each.

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Regards,

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Martin

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On Thu, Oct 3, 2024 at 04:57 PM, vbifyz wrote:

Mike,

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With a respect to your thoghts to ascertain? the common mode rejection by a loop antenna has nothing to do with the introduction of concept -? injection of test signal through?a dummy aerial circuit. Basically it is related to the tests as follow: frequency response of active antenna, measuring the levels of intermodulation products with two tone test etc.

Your worry? is related more to a shielded loop antenna and for that is used a different test setup.

It is a false anticipation to throw in one pot all different tests for active antennae.

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Regards,

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Raphael

Hi All,

Northon measurement setup

The Norton equivalent circuit is very convenient model for the wideband active loop. In production tests we have the following setup : Signal generator, followed by 1:1 balancing transformer loaded with 50 ohms to have flat frequency response. The secondary is connected ?via two resistors? of 1 Kom to the amp. loop input. The dummy inductance is 2 uH parallel to the input. The maximal ?amp. input impedance at highest frequency is somewhere of 100 ohms .? With 2 Kom source impedance the sig. ?generator can be assumed as a current source. ?The measured frequency response follows closely the spice model. ?But this model cannot represent correctly the true antenna factor above some frequency since the loop cannot be assumed as a pure inductance ?due to transmission line effects.? Even in the case where we use in the same measurement setup? a ?real loop instead of dummy inductance.? The problem is that the injection current from the real loop ?is quite different there and Norton model with fixed current ?is not reliable.? If we apply the rule that the small loop maximal circumference must be 10 times shorter than the wavelength, at this specific frequency the loop Z is approximately 25 % larger than the Z of equivalent dummy ?inductance which shows already ?significant transmission line effects. ?So above these frequencies we must be very careful in interpreting the results for the real antenna factor.? What we are interested is the frequency response of the antenna factor not the frequency response of the amplifier. ?For example, it is not clear that the peak ?of several dB at 40 MHz in frequency response in our amp. ?which can be measured with above setup ??will exists in the real antenna factor response.

?This can be modeled in NEC? - make a simple loop model? - load it with amp. input impedance? and create a vertical plane wave ?field? and calculate the induced currents into the load. Then we can apply the calculated ?currents in the spice amp. model and get realistic antenna factor frequency response of this active loop. Unfortunately I cannot do that in MMANA (MININEC) which I use since there we cannot create a EM field.? So if someone is familiar with NEC, this numerical experiment will be quite interesting to be performed and will be very close to the real loop performance. The absolute measurement of the loop antenna factor is complicated and needs calibrated? measurement equipment but the relative frequency response? obtained with NEC will be quite informative.

As a resume : up to certain frequency this Norton measurement setup ?is quite reliable; ?above it, using dummy inductance ,will not give reliable results. ?For single 1 m diam loop? this frequency is probably somewhere at? 10 MHz. For two 1 m diam crossed co-planar loops it is somewhere at 15 MHz.

P.S. To Mike – The CM rejection is important. The measured common mode rejection for sample AAA1 loop amp. at 3 MHz ?is? 38 dB when CM source is between shorted input and signal ground , ?60 dB when CM source is connected to power supply ground and 80 dB when CM source is connected to protective earth terminal (marked GND on the PCB). ?So connecting a protective ground does not impair the amp. performance.? These are worst case ?measurements where no CM baluns are inserted? in PS and FTP cables. ?The dummy loop does not take place in this measurement since the amp. input is short circuited. ?In production we measure the IP2 ?which is? closely related to CM? rejection and it is easier to be measured.

Chavadar LZ1AQ????? www. lz1aq.signacor.com

Hi Chavdar.

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Thanks for this note.

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Just to be clear, is the circuit shown in the photos section an accurate representation of what you are proposing.

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It should be possible to produce a suitable parallel resonance, as would be the case with an actual loop, by adding a shunt capacitor, which I have shown as Cp.

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Regards,

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Martin

Hi All,

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When we introduced the concept of "dummy" areial model the intention was to use an injected test signal for a variety of small active loop antennae ( unshielded and shielded untuned ) as well as for different designed antenna amplifiers not focusing on? LZ1AQ design only.

Also, as Martin pointed out the bandwidth for test should include as well as frequency where the small loop antenna creates parallel resonance and certain persentage beyound that frequency point.

Otherwise, it reminds me a saying: give to the baby any toy letting him stop of crying...

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On our table are so far three proposed " dummy" aerial models:

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1. Levkov's - high pass filter of 1st order (RL )

2. Lim's? ? ? - high pass filter of 2nd order (CL )

3. Wasserman's - low pass filter of 2nd order (LC)

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Any dummy aerial model must replicate with a certain degree the performance of actual physical antenna.

Let's for sake of argument exclude from our discussions which of three proposed models are appropriate as a dummy aerial circuit for small loop antennae.

We will look at the physics of behavior of magnetic loop antenna, excluding from discusions the electrical field and distributed antenna capacitance.

Based on Faraday's law, into the closed loop is created a current of magnetic field that flows through a number in series of lumped distributed elements such as antenna inductance, radiation and wire losses and impedance load ( input of our antenna amplifier ).

Saying that, the current value will decrease with frequency due to the inductance in series and subsequentally the voltage on our load will follow this decrease.?

Now let's go back to the proposed dummy models with high pass filters - with increase the test signal frequency the voltage drop on load will increase as well.

Does that contradict what happens with the applied signal to the load impedance ( the voltage on load impedance shall decrease with frequency rise, remember we excluded from our discussions the first parallel resonance ) ??

Secondly, in Levkov's dummy aerial configuration are two 1 Kohms resistors in series arm of his voltage divider.

I think these selected value of resistors will change the Q - factor of replicated loop antenna lowering it.

Thirdly, if in our discussion is introduced AF antenna factor of loop antenna that can be calculated with Owen Duffy's proposed calculator ( his assumptions for this calculation are - antenna perimeter less than 3/10 of wavelength, wire round, wire bare and mon-magnetic ). So, AF of small loop antenna decreases with frequency.

That tells me combined amplitude frequency response of small loop antenna experience an attenuation with increase? of frequency, therefore a low pass filter will more precisely mimics the small loop antenna.

Interesting that input of antenna amplifier for all three proposed layouts of dummy antenna will see the antenna inductance in parallel to the amplifier input but that is the only commonality...

In addition, you may look at published technical papers by members of IEEE related to loop antennae.

The equivalent model of small loop antenna is LPF for Thevenin's voltage source configuration.

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Regards,

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Raphael?

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To Martin,

Yes this is the measurement circuit. But the problem is not the resonance of the dummy inductance? to be the same as the actual loop,? but the equivalent current source value which is different when the loop becomes not so small. In the region of frequencies where the loop is really small ( <1/10 wavelengths) ? the induced? current is constant and does not depends on frequency if the loop works in short circuit mode which is almost our case.

Chvadar lz1aq

Martin,

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I can understand that Levkov's proposed and used by him designed "dummy" aerial cicuit? ?addresses only the frequency region where it is observed short circuit mode by placing the inductor element? in the shunt arm.

Well, in order to meet this condition the active small loop antenna shall be designed with relatively smaller antenna inductance ( probably by using many in parallel loops? or changing our design philosophy by using transimpedance amplifiers instead of )

since we have been? interested to cover a broader frequency band up to 30 MHz.

Secondly, his dummy aerial circuit does not address AF ( antenna factor ) of loop antenna that decreases with frequency.

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Regards,

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Raphael

To Raphael,

The Thevenin and Norton representation of 2 pole circuit? will give the same result and using one of them is a matter? to simplify the calculations and measurements. ?For wideband short circuit loop, ?Norton model is much simpler since the current source is constant . ?If you want to measure the amp. loop frequency response with voltage source (Thevenin model) ?you should have to increase the voltage from the signal generator linearly with frequency as Faraday law says. The Thevenin model of a small loop is physically more acceptable since there you can associate the values of the equivalent circuit directly with the parameters of the loop –its inductance, parasitic capacitance, loss resistance and rad. resistance. Transforming them into parallel Norton model give ?not so meaningful ?values. But both models at higher frequencies ?will give the same wrong results if we assume that the induced voltage ?is predicted only by the simple Faraday law. Any ?dummy inductance approach will be ?reliable only for low frequency region. For higher frequencies you can? set? the resonant point of a dummy inductance as you wish with any parallel capacitance, or LP or HP filters etc. ??that will resemble the actual loop behavior ?but you do not know the law that ??actual e.m. force follows (induced by e.m. field) ?and hence the measured antenna factor response there ?will be wrong. ?The antenna factor ?at higher frequencies? is ?what ?I want to model and what is interesting , not the amp. frequency response with dummy inductance. NEC modeling is what can help as I suggest in previous post.

Regards, Chavdar lz1aq

OK, I understand the various constraints, and I appreciate everyone's input.

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Now that winter is approaching, I'd prefer to be inside the workshop, in the warm and dry, rather than fiddling with loop amplifiers outdoors, in the cold, dark, wet

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So for the time being, I'll stick with my transformer based "simulator", which serves my purpose, and seems to give results that are similar to using an actual loop, energised via a close coupled source loop.? In fact, if you coiled up the loops, so they could fit inside a small box, wouldn't that be very much like my transformer design ?

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I'll let you folks figure out something that is better, as we just seem to be going around in a loop, pun intended...

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Regards,

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Martin

Hi Chavadar,

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I ran a simple loop model in EZNEC Pro+ version 7.0. The simulated loop is an octagon with dimensions that approximate a one meter diameter circular loop. Conductor diameter is 3.3 mm. Excitation is a 1V/m plane wave. The loop was modeled in free space. A resistive load of 0.1 Ohms (essentially a short circuit) was placed across the feed-point. I also ran a simulation for feed-point impedance.

The short circuit current (i.e. the Norton equivalent source current) is constant within 0.2 dB up to 30MHz.? This is much flatter than I would have expected.? I was equally surprised that the short circuit current at resonance was only 0.4dB higher than the value at low frequencies.? I have not used this software much but I believe I did everything right.

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I will upload the simulation file to Files.

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- Mark

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Hi Mike,

A dummy (& test procedure) for testing the common mode rejection already exists in IEC315-1, Fig. 7. The original IEC standard is behind a paywall, but a nearly identical Indian standard is free at the link below:

https://ia601904.us.archive.org/33/items/gov.in.is.12193.1.1989/is.12193.1.1989.pdf

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Hi Chavdar,

Thank you very much for sharing the details of your dummy. It will be very useful for the testing of my homebrew LZ1AQ preamps, in adjunct to my own dummy. However, I am unsure if I have correctly understood the above paragraph. Does it mean your dummy is usable up to 10 MHz only?? And regarding the last sentence, do I need to modify the dummy when testing pre-amps intended for crossed co-planar loops? Thanks.

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73, Chin-Leong Lim, 9W2LC

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On Fri, Oct 4, 2024 at 08:25 PM, Mark Whittington AG5RT wrote:

I ran a simple loop model in EZNEC Pro+ version 7.0.

Excellent Mark,

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Thank you for your efforts. The simulation result sheds light into the issue.

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regards, Fred

On Fri, Oct 4, 2024 at 11:25 PM, Mark Whittington AG5RT wrote:

The short circuit current (i.e. the Norton equivalent source current) is constant within 0.2 dB up to 30MHz.? This is much flatter than I would have expected.? I was equally surprised that the short circuit current at resonance was only 0.4dB higher than the value at low frequencies.?

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Should have said, that particular data was for a 36 segment, 1 meter diameter loop, zero conductor resistivity, 25.4mm diameter conductor, excited by a 1V/meter plane wave into a 1 MEG load.? Resonance estimated to be about 43.3 MHz.

Dan, could you please share your EZNEC file?

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Regards

Fred

In a message dated 10/5/2024 11:07:25 AM Central Daylight Time, wassermanr46@... writes: