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Steve ugly-build LZ1AQ using MPS2222 sweeps uploaded to Photos
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Basically you are using a simple jig consisting of RF isolation transformer and voltage dividers 24/0.5 ohm.
My idea has been different based on a standard using a dummy antenna circuit recommended for use in testing broadcast receivers. It was published old article by W.Swinyard in 1941 " Measurement of Loop Antenna Receivers" , where two coupled loop antennas were used for distances between them less than wavelength but greater than diameter of larger of two loops ( transmit or receive ). I have been considering to construct a different jig/ dummy antenna circuit consisting of pi-type attenuator with unequal shunt arms - towards generating source 50 ohm resistor and towards antenna amplifier 2 ohm resistor or 0.5 ohm. Between the attenuator and input of amplifier under test to be included additional circuit that represents dummy loop antenna - series arms of fixed inductances, say 700 uH or more ( La/2 ) and shunt arm - fixed capacitor ( Ca ). Regards |
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Biastee,
1. The values of inductances are L1=L2=La/2 and C=Ca based on S11 measurements for a particular loop antenna. So, the dummy circuit is a simple Pi- attenuator balanced with 50 ohm resistor in shunt arm towards the generator port and 0.5 or 2 ohm resistor in shunt arm towards the amplifier under test. In addition, between the attenuator and input ports of amplifier under test to include as well as a dummy antenna circuit consisting of series arms L1=L2=La/2 and shunt arm towards amplifier C=Ca. 2. I am not sure if the LPF in LZ1AQ's design serves as an equalizer for the frequency response of the amplifier from 15 to 25 MHz. I crossed another paperwork, where was presented S21 of this LPF. At frequency 20.05 MHz -5dB drop, at 40.05 MHz a further drop -35 dB, at 60 MHz -60 dB and at 80.05 MHz -70 dB. Also, the frequency response of amplifier itself with added just two capacitors 100 pF but without the LPF filter: S21 - for BW=125 KHz - 27 MHz +/- 3 dB I agree the inductances 300 nH will increase the input impedance of the amplifier but it might with parasitic input capacitance of amplifier to roll off at 20.5 MHz the frequency response of amplifier. Regards, Raphael |
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On Sun, Jul 14, 2024 at 03:17 AM, <biastee@...> wrote:
Can you kindly post a circuit diagram?My circuit is intended to simulate a loop with a loosely coupled 50 Ohm port. All the following plots are taken from the "loop" side of the simulator, with the 50 ohm port terminated in 50 ohms. Simulated performance on Smith chart. /g/loopantennas/photo/267767/3805545 Measured performance on Smith chart. /g/loopantennas/photo/267767/3805549 Impedance chart /g/loopantennas/photo/267767/3805547 Regards, Martin |
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On Sun, Jul 14, 2024 at 03:45 PM, Martin - Southwest UK wrote:
/g/loopantennas/photo/267767/3805545Try /g/loopantennas/photo/267767/3805545 |
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On Sun, Jul 14, 2024 at 03:47 PM, Martin - Southwest UK wrote:
Try /g/loopantennas/photo/267767/3805545Still not working Try /g/loopantennas/photo/267767/3805545 |
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Martin, Mike and Chin-Leong
I analyzed again any suitable test networks for measurement of S21 for active small loop antenna ( not just antenna amplifier ). Martin used coupled loop antennas in the near-field, where only magnetic field present. I guess it is only acceptable method currently at least reading literature related to this field. Since it this measurement is involved magnetic flux density of excitation loop that is created by current flow in this antenna. We should worry the current for a wide frequency range is maintained almost the same due to the inductance of excitation antenna. I propose in series with this excitation loop include a fixed current limiting resistor which value is calculated as follow: Rlim= 2 pi x f c x L a where fc - highest broadband frequency used for S21 measurement of active loop antenna. So, within 3 dB the current in excitation loop will be maintained the same from 0 to fc frequency. Let's discuss any shortcoming of proposed. Regards, Raphael |
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On Mon, Jul 15, 2024 at 06:24 PM, Raphael Wasserman wrote:
within 3 dB the current in excitation loop will be maintained the same from 0 to fc frequency. Hi Raphael.
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OK, so this applies to the excitation of the reception loop, by means of a smaller source loop.
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Are we talking about the inductance of the reception loop, or the excitation loop, I assume it is the latter.
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The small excitation loop I used, had an inductance of approximately 300nH, and if we take 30MHz as the upper limit, then I calculate the required resistor value to be around 50 Ohms.
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During my tests, I placed a 10dB resistive attenuator between the excitation loop and 1:1 balun, and the coax to the generator.
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This can be seen in the photo of my test setup. The small black box with the white label is the 1:1 balun transformer. The black thing below it, is a clip-on ferrite, to provide a bit more choking impedance around 50MHz.
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I fitted the attenuator as a precaution, so that the generator wouldn't attempt to level the output during a sweep, when presented with a non 50 ohm reactive load.
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However, I believe it would also have performed the function you are suggesting.
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Regards,
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Martin |
开云体育Hi Martin, ? We are talking about the small excitation loop that is ?interfaced to CH0 port of VNA. Yes, you are correct the current limiting resistor will be 50-56 Ohms for the specified upper frequency 30 MHz. I constructed a similar small loop from 3 mm copper wire and soldered SMD type two small in parallel 100 Ohms resistors using SMA connector as well. I am still not giving up the idea – avoidance off coupled loops but using a dummy circuitry that represents impedance response of a receive loop antenna for frequency range 1-32 MHz. If you remember in old days for measurement the sensitivity and tuning shortwave receivers were used dummy circuitry between the signal generator and input port of receiver. The dummy circuitry represented impedance of open-wire type antenna in MW and SW bands. ? Regards, Raphael ? From: [email protected] <[email protected]> On Behalf Of Martin - Southwest UK via groups.io
Sent: Monday, July 15, 2024 3:51 PM To: [email protected] Subject: Re: [loopantennas] Steve ugly-build LZ1AQ using MPS2222 sweeps uploaded to Photos ? On Mon, Jul 15, 2024 at 06:24 PM, Raphael Wasserman wrote:
Hi Raphael. ? OK, so this applies to the excitation of the reception loop, by means of a smaller source loop. ? Are we talking about the inductance of the reception loop, or the excitation loop, I assume it is the latter. ? The small excitation loop I used, had an inductance of approximately 300nH, and if we take 30MHz as the upper limit, then I calculate the required resistor value to be around 50 Ohms. ? During my tests, I placed a 10dB resistive attenuator between the excitation loop and 1:1 balun, and the coax to the generator. ? This can be seen in the photo of my test setup. The small black box with the white label is the 1:1 balun transformer. The black thing below it, is a clip-on ferrite, to provide a bit more choking impedance around 50MHz. ? ? I fitted the attenuator as a precaution, so that the generator wouldn't attempt to level the output during a sweep, when presented with a non 50 ohm reactive load. ? However, I believe it would also have performed the function you are suggesting. ? Regards, ? Martin |
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On Mon, Jul 15, 2024 at 08:30 PM, Raphael Wasserman wrote:
If you remember in old days for measurement the sensitivity and tuning shortwave receivers were used dummy circuitry between the signal generator and input port of receiver. Yes, I use a 50 ohm load and series capacitor to test my E-Probe type active whip amplifiers.
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Choose, the value of capacitor to match that of the whip. It's a perfectly valid test technique, referred to as the equivalent capacitance substitution method.
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We are looking for the equivalent inductance substitution method, but the self resonant frequency messes this up and stops it being a pure inductor.
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Otherwise, I guess something like a generator with a low value of source impedance, and a simple series inductor would do the job, but maybe with a capacitor across the inductor to produce the required self resonance.
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Regards,
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Martin |
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There is a better known and internationally recognized method for coupling to a magnetic antenna in IEC315-1. Like Swinyard, the IEC method is also intended for broadcast receivers. Again, the measurement is in the near field, but I suspect the given equations do account for it. The setup is shown in the following diagram:
/g/loopantennas/photo/296366/3805879 IEC315-1 is located behind a paywall, but the Indian government has made available a free version at:?
https://ia601904.us.archive.org/33/items/gov.in.is.12193.1.1989/is.12193.1.1989.pdf > I have been considering to construct a different jig/ dummy antenna? > circuit consisting of pi-type attenuator with unequal shunt arms - towards? > generating source 50 ohm resistor and towards antenna amplifier 2 ohm? > resistor or 0.5 ohm.? ?
One problem that I can foresee is - the dummy antenna's attenuation will impede the use of hobby-grade VNAs (e.g. nanoVna) because of their limited dynamic range.?
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> Between the attenuator and input of amplifier under test to be included?
> additional circuit that represents dummy loop antenna - series arms of? > fixed inductances, say 700 uH or more ?
Do you mean 700 nH (0.7 uH) instead of 700 uH? The 700 nH x 2 series arm inductances means the loop must have been made from a very fat tube because according to LZ1AQ, 1.7 uH represents a loop with a 40mm diameter conductor! For "normal" 3.4 mm dia. wire, LZ1AQ specified 3.6 uH. ?
> I am not sure if the LPF in LZ1AQ's design serves as an equalizer? > for the frequency response of the amplifier from 15 to 25 MHz. > I crossed another paperwork, where was presented S21 of this LPF.? > At frequency 20.05 MHz -5dB drop, ?
Simulation shows the gain reaches a peak at 28 MHz (blue trace in the graph linked below). At 30 MHz, there is a ~ 1 decrease from the peak. The response without the LPF is also shown for comparision (red trace). Without the LPF, the gain is significantly reduced over 15 ~ 30 MHz.?
/g/loopantennas/photo/296366/3805459 However, my experimental prototypes exhibit peak gain at ~23 MHz; i.e. ~23% lower than simulated. At 30 MHz, the experimental gain decreases 5 dB from the peak. I have not determined the cause of the discrepancy between simulation and experimental. ?
/g/loopantennas/photo/296366/3805017 I suspect the experimental peak frequency can be shifted back to 30 MHz by either reducing L1-2 or the 100 pF cap (C5 & C10).?
/g/loopantennas/photo/296366/3805458 ?
> My circuit is intended to simulate a loop with a loosely?
> coupled 50 Ohm port. All the following plots are taken? > from the "loop" side of the simulator, with the 50 ohm? > port terminated in 50 ohms. ?
Hi Martin,
My simulation agrees with yours that your prototype dummy has a coupling factor k ~ 0.7. To better approximate your loop aerial's impedance, k = 0.2 is required.? /g/loopantennas/photo/296366/3806328 Incidentally, the 60s era's frequency discriminator coils achieved k = ~0.3 at 10.7 MHz by using an open magnetic path (solenoid) and separate cores. Photo of the aforesaid in fig. 1 of the following article: www.researchgate.net/publication/353832328_What_simulation_of_the_Foster-Seeley_discriminator_can_reveal
73,
Chin-Leong Lim, 9W2LC. |
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> If you remember in old days for measurement the?
> sensitivity and tuning shortwave receivers were? > used dummy circuitry between the signal generator? > and input port of receiver. The dummy circuitry represented? > impedance of open-wire type antenna in MW and SW bands. ?
The IEC315-1 standard, referred to in my previous comment, also described MW & SW dummies for open-wire aerials 10m long, 5m long, and a short whip on car boot connected with a coax cable. The nomenclature used by IEC315-1 is "antenna simulation network". "Dummy antenna" is the jargon used by a previous employer of mine. ?:-)?
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73,
Chin-Leong Lim, 9W2LC. |
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Basically you are using a simple jig consisting of RF isolation transformer and voltage dividers 24/0.5 ohm. My idea has been different based on a standard using a dummy antenna circuit recommended for use in testing broadcast receivers. It was published old article by W.Swinyard in 1941 " Measurement of Loop Antenna Receivers" , where two coupled loop antennas were used for distances between them less than wavelength but greater than diameter of larger of two loops ( transmit or receive ). I have been considering to construct a different jig/ dummy antenna circuit consisting of pi-type attenuator with unequal shunt arms - towards generating source 50 ohm resistor and towards antenna amplifier 2 ohm resistor or 0.5 ohm. Between the attenuator and input of amplifier under test to be included additional circuit that represents dummy loop antenna - series arms of fixed inductances, say 700 uH or more ( La/2 ) and shunt arm - fixed capacitor ( Ca ). Regards |
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Hi Chin-Leong,
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You are correct, I used the 61Mix core as I had that to hand at the time.
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I have just wound a 2uH inductor, 20t overwound on a 5mm plastic rod (offcut of variable resistor spindle).
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It has a self resonant frequency at around 35MHz.
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I have overwound this with 5 to 10 turns (to vary the coupling) as the 50 ohm coupling port, and it is very much closer to an actual loop, in terms of its impedance and Smith chart curves.
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I'm a bit concerned about the LF end of the S21 plot, and it maybe that there isn't enough coupling due to lack of a ferromagnetic core, but it could be correct, and simply due to the extreme mismatch loss that would be expected at these frequencies.
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A bit more experimentation is required, but it looks to be very promising.
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Regards,
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Martin
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On Tue, Jul 16, 2024 at 04:46 AM, <biastee@...> wrote:
My simulation agrees with yours that your prototype dummy has a coupling factor k ~ 0.7. To better approximate your loop aerial's impedance, k = 0.2 is required.? |
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Hi Fred,
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the maths are a bit too deep for me, but I get the impression that once again it is concentrating on a small loop, below resonance, with a linear current distribution.
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What we are trying to produce is a small test "jig", that allows us to simulate the characteristics of an actual 1m diameter loop, that has a self resonance somewhere above 30MHz, which is typical of those being used in conjunction with the LZ1AQ and Wellbrook amplifiers.
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I think an air spaced inductor, tuned to resonance at just above 30MHz, with a loosely coupled excitation coil, is actually very similar to the two loop calibration method. Except that it can be contained in a small box, which is far more convenient for use on the test bench, and doesn't require a screened room.
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We just need how to equate the coil ratios and coupling factors, to be equivalent to using two loops on a test range.
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Regards,
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Martin
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On Tue, Jul 16, 2024 at 02:34 PM, Fred M wrote:
This article may help to better understand the coupling between excitation loop and receive loop. |
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Chin-Leong,
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I meant the series arms of a dummy antenna circuitry ( equivalent of small loop antenna ) should have fixed inductances of value La/2, based on specific untuned small loop antenna. Yes, I realize because? lack of standard and? everyone designs his own - these inductances will have a wide range. For example, LZ1AQ - 1.8 uH each.
IEC 315-1 "Methods of Measurement On Radio Receivers For Various Classes of Emission" standard is unreachable for me and paying $119 for it does not make sense at all.?
I noticed your comments to Martin regarding the coupling factor. I guess, for loop antennae we can not use coupling factors but S21 as a coupling between excitation antenna and receive loop antenna because we should follow certain condition for the distance between antennae in near field? ?2R < distance < Lambda/ 2 Pi, where R is the radius of larger of two antennae. I refer to IEEE Standard on Broadcast and Television Receivers ( IRE-1941-07 ).? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?However, coupling factor can be used when a small excitation loop antenna is mounted directly in a larger loop antenna plane that is more applicable for transmit antennae design.?
Your other comment about 10.7 MHz frequency discriminator where magnetic coupling between coils was ~0.3, it is done for a reason to get a wider linear bandwidth of 250 KHz? between magnetically coupled coils similarly it was done in designing a frequency selective IF of 455 KHz, using three coils( parallel resonant circuits ) with two fixed capacitive couplings between them which later was replaced with quartz filters...
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Regards,
Raphael?? |
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> IEC 315-1 "Methods of Measurement On Radio Receivers
> For Various Classes of Emission" standard is unreachable? > for me and paying $119 for it does not make sense at all.? ?
Had you read my reply carefully, you would have noticed a link to download the aforementioned document for free.?
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> I noticed your comments to Martin regarding the coupling?
> factor. I guess, for loop antennae we can not use coupling? > factors but S21 as a coupling between excitation antenna? > and receive loop antenna ?
My comments to Martin pertain to his dummy network which used a transformer; i.e. it is NOT about loop antennas. The coupling factor referred to is the one between primary and secondary windings in the transformer. ?
73,
Chin-Leong Lim, 9W2LC. |
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Agreed, but I think we can relate the transformer coupling factor, to S21, and therefore the distance between loops when using the test range method of calibration.
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At least, it is my hope, that we can come up with a formula that allows us to emulate the test range method in a small network, and be able to calculate "real world" values.
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On Wed, Jul 17, 2024 at 02:13 AM, <biastee@...> wrote:
The coupling factor referred to is the one between primary and secondary windings in the transformer. |
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Chin-Leong and Martin,
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I downloaded IEC 315-1 standard.
Item 20 - "Antenna Simulation Networks ( Artficial Aerials )" basically covers three type of antennas: open-wire antenna 100 KHz - 30 MHz, rod and telescopic antennas?
and multiturn loop antenna ( not an active small loop antenna ! ).?
Item 20.3 - "Criteria" ( for designing antenna simulation networks ):
1.? The network shall present to the receiver an impedance as nearly equal as necessary to that of the real antenna over the required frequency range.
2.? The network impedance shall match the source impedance of the signal source to a sufficient degree of accuracy.
3.? The attenuation of the network shall not vary very rapidly with frequency and shall be as is reasonable practicable.
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From other source of information regarding the excitation loop antenna that is connected to generator source for near field measurements - two conditions shall apply:
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a)? Distance between excitation loop and receiving loop? ? C <? d? < Lambda/ 2 pi, where C - circumference of larger of two loops
b)? Uniform current in the excitation loop Cexc << Labda /16 , where Cexc - circumference of excitation loop for a specified frequency range 1- 30 MHz
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In my opinion, without IMN ( broadband impedance matching network ) item # 2 cannot be fullfilled easily although between the source and artificial network ( dummy antenna ) will be used attenuator.?
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Raphael
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Ikin knew all that decades ago !!!!!!!!!!
On Wednesday, July 17, 2024 at 12:55:19 p.m. EDT, Raphael Wasserman <wassermanr46@...> wrote:
Chin-Leong and Martin,
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I downloaded IEC 315-1 standard.
Item 20 - "Antenna Simulation Networks ( Artficial Aerials )" basically covers three type of antennas: open-wire antenna 100 KHz - 30 MHz, rod and telescopic antennas?
and multiturn loop antenna ( not an active small loop antenna ! ).?
Item 20.3 - "Criteria" ( for designing antenna simulation networks ):
1.? The network shall present to the receiver an impedance as nearly equal as necessary to that of the real antenna over the required frequency range.
2.? The network impedance shall match the source impedance of the signal source to a sufficient degree of accuracy.
3.? The attenuation of the network shall not vary very rapidly with frequency and shall be as is reasonable practicable.
?
From other source of information regarding the excitation loop antenna that is connected to generator source for near field measurements - two conditions shall apply:
?
a)? Distance between excitation loop and receiving loop? ? C <? d? < Lambda/ 2 pi, where C - circumference of larger of two loops
b)? Uniform current in the excitation loop Cexc << Labda /16 , where Cexc - circumference of excitation loop for a specified frequency range 1- 30 MHz
?
In my opinion, without IMN ( broadband impedance matching network ) item # 2 cannot be fullfilled easily although between the source and artificial network ( dummy antenna ) will be used attenuator.?
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Raphael
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