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Re: Optimizing Small Untuned Loop Antennas
John, I forgot to mention in the final equation of AF Is indirectly included the aperture value of antenna through the antenna gain G because any antenna gain is dependent on its aperture value. Regards, Raphael Отправлено с iPhone
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27 окт. 2022?г., в 8:13 AM, Raphael Wasserman via groups.io <wassermanr46@...> написал(а):
? All, I see some of responders are confused about AF definition ?and variables that effect AF value.? I did not call AF as a loss factor, only made my point about “mismatch factor” caused by different Impedance receive antennas regarding the free space Impedance value.? Regards Отправлено с iPhone 26 окт. 2022?г., в 11:05 PM, VE7VXO <jstreet@...> написал(а):
?The antenna factor is strictly a function of the effective aperture of the antenna.? For a given power density the ratio of the free space impedance and the system impedance form a factor which is a constant.? The constant would be different in a 50 ohm system vs a 75 ohm system and yes you can call this a factor but your original post calls this a "loss factor".? This factor does not imply anything is lost, if so it would be a violation of conservation.
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Re: Optimizing Small Untuned Loop Antennas
All, I see some of responders are confused about AF definition ?and variables that effect AF value.? I did not call AF as a loss factor, only made my point about “mismatch factor” caused by different Impedance receive antennas regarding the free space Impedance value.? Regards Отправлено с iPhone
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26 окт. 2022?г., в 11:05 PM, VE7VXO <jstreet@...> написал(а):
?The antenna factor is strictly a function of the effective aperture of the antenna.? For a given power density the ratio of the free space impedance and the system impedance form a factor which is a constant.? The constant would be different in a 50 ohm system vs a 75 ohm system and yes you can call this a factor but your original post calls this a "loss factor".? This factor does not imply anything is lost, if so it would be a violation of conservation.
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Re: Optimizing Small Untuned Loop Antennas
The antenna factor is strictly a function of the effective aperture of the antenna.? For a given power density the ratio of the free space impedance and the system impedance form a factor which is a constant.? The constant would be different in a 50 ohm system vs a 75 ohm system and yes you can call this a factor but your original post calls this a "loss factor".? This factor does not imply anything is lost, if so it would be a violation of conservation.
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Re: Optimizing Small Untuned Loop Antennas
All, ? In recent years the use of a term called “Antenna Factor” in EMC and spectrum pollution work has become very important. There has been a great need for measuring field intensity and/or power density as accurately and conveniently as possible. Classically in RFI/EMI measurements, the use of antenna factors is very common. These antenna factors were, by definition, the conversion of two-terminal receiver voltages to field intensity. The recent deployment of computer controlled receiving systems with analysis capable capabilities has added a few need for examining the antenna factor. Depending on the type of test that antenna may include factors such as: 1. Loss due to mismatch of impedance between the antenna output connector and transmission line, 2. Loss due to Attenuation of the transmission line, 3. Loss due to VSWR of the transmission line, 4. Gain due to a preamplifier located at the antenna, 5.Loss due to the mismatch of impedance at the input of the receiver. They may be calculated, measured or obtained from published charts. If any of the above factors are included in an antenna factor AF, it should be stated so as to avoid misinterpretation. ? Let’s continue further. From the radio engineers handbook the rated power density is: ? Po= Pr/A, where Pr= receiver power and A=effective area of antenna ? In addition, A= Gx Wavelength^2/4 pi and combining both equations together: Po= Pr/Gxwavelength^2/4 pi, where G= antenna gain (numeric ). ? Again from the radio propagation theory is known: Po= Eo^2/Zo where Eo=field intensity and Zo= impedance of radiating media ( 377 ohms for free space ) ? The power at the receiver is: Pr=Vr^2/Zr where Vr=voltage at the receiver and Zr= receiver input impedance or it can be Za= receive antenna impedance . ? Substituting the expressions for Po and Pr of equations above we can have: E0^2/Zo= Vr^2/Zr/G xwavelength^2/4 pi ? I will drop other mathematical conversion reaching to a final: ? 20logEo-20logVr=10logZo/Zr-Gdb-20log wavelength + 10log 4pi ? By definition antenna factor is: ? AF= 10log Zo/Zr -Gdb-20log wavelength + 10 log4pi ? Many practical applications of antenna factors are in” free space” environment. This is, in general, true for antennas used outside which are directive and are not pointed with low grazing angles. When ground effects are to be considered, the source impedance Zo must be modified accordingly. ? For free space (377 ohm ) and 50 ohm receiving system we have the impedance ratio expressed in dB as follows: ? 10log377/50=8.8 dB – ( that we call a”mismatch factor” ) ? So, the final practical equation for AF: ? AF=19.8-GdB-20 log wavelength ? Also, please remember that we are considering here not radiation resistance of antenna or input resistance of receiver but their impedances. Another point in, RFI/EMI fields of measurements we deal with calibrated receive antennas where their impedance is really matched to 50 ohms and receiver input presents as well as 50 ohms impedance ( full match) and we may substitute Za with Zr because both are 50 ohms. ? I guess, my “lecture” has not been very annoying. Any measurements start with science and mathematics… ? Regards, ? Raphael ? ? ? ? ? ? ?
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From: [email protected] < [email protected]> On Behalf Of Steven Greenfield AE7HD via groups.io Sent: Wednesday, October 26, 2022 7:49 PM To: [email protected]Subject: Re: [loopantennas] Optimizing Small Untuned Loop Antennas ? On Wed, Oct 26, 2022 at 01:47 PM, VE7VXO wrote: Why should an antenna's radiation resistance match that of free space impedance and I'm not sure the theory of maximum power transfer (ie impedance matching) applies in that case.
Yes, I thought the function of an antenna (part of it) is to act like a coupling device that transforms the feedpoint impedance to that of free space. Not that the antenna should have the impedance of free space at the feedpoint. Am I wrong?
?
--
Steve Greenfield AE7HD
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Re: Optimizing Small Untuned Loop Antennas
Already a thing, Rick.? The latest firmware for the KiwiSDR
outputs a CAT string on /dev/tty/usb0 with its tuned frequency.?
Connect this to a tracking magloop tuner (a number of fine designs
exist - the code could be tweaked to output a varactor voltage for
an rx only antenna rather than drive a stepper motor if desired)
and you have the advantage of a small and efficient antenna but
the ability to work around its narrow band nature.
? With the excess gain that modern receivers have at HF
especially the low end where compact antennas are attractive, the
AGC action will still reveal signals that may be of interest
outside the resonant envelope of the tuned antenna.? Click on the
area of interest and presto the antenna follows you there.? Or
take the old school approach of slowly tuning up the band while
the antenna follows.
If you are panadapter obsessed and must have a broadband antenna
which can cover the entire HF spectrum, by definition
(Chu-Wheeler) it must be lossy and reactive.? What does it mean
then to "optimize" it??? In my opinion a compact efficient and
therefore narrowband antenna which is frequency agile is an
awesomized antenna.
On 2022-10-26 4:25 p.m., Richard
\(Rick\) Karlquist \(N6RK\) wrote:
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One could imagine a swept receiver (wouldn't have to be SDR)
that was synchronized with a swept loop antenna to make a
"Panadapter" display.
Would that work for you?
On 2022-10-26 16:19, Everett N4CY via groups.io wrote:
Most
of us these days are using SDR receivers and want to look at a
wider piece of spectrum than the small amount you will see with
a tuned loop. Are we going forward, or backwards?
?
Everett N4CY
?
As a bonus you also get protection from out of band
signals overloading the front end of your rx by virtue
of the antenna acting as a narrow RF filter.
?
On 2022-10-26 02:03 PM, Richard
\(Rick\) Karlquist
\(N6RK\) wrote:
You can get a lot more signal out of a given
loop if you tune it.
Also,?you get 9 dB additional
signal every time you double
the diameter of the loop.
Do you have some requirement that prevents you
from simply using a tuned loop?
On n6rk.com you can find my article on building
tuned loops.
Many people have duplicated this design.
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Re: Optimizing Small Untuned Loop Antennas
On Wed, Oct 26, 2022 at 01:47 PM, VE7VXO wrote:
Why should an antenna's radiation resistance match that of free space impedance and I'm not sure the theory of maximum power transfer (ie impedance matching) applies in that case.
Yes, I thought the function of an antenna (part of it) is to act like a coupling device that transforms the feedpoint impedance to that of free space. Not that the antenna should have the impedance of free space at the feedpoint. Am I wrong? ? -- Steve Greenfield AE7HD
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Re: Optimizing Small Untuned Loop Antennas
KISS is always the best approach.
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On Oct 26, 2022, at 6:25 PM, Richard \(Rick\) Karlquist \(N6RK\) <richard@...> wrote:
?
One could imagine a swept receiver (wouldn't have to be SDR) that was synchronized with a swept loop antenna to make a "Panadapter" display.
Would that work for you?
On 2022-10-26 16:19, Everett N4CY via groups.io wrote:
Most of us these days are using SDR receivers and want to look at a wider piece of spectrum than the small amount you will see with a tuned loop. Are we going forward, or backwards?
?
Everett N4CY
?
On Oct 26, 2022, at 6:07 PM, VE7VXO <jstreet@...> wrote:
As a bonus you also get protection from out of band signals overloading the front end of your rx by virtue of the antenna acting as a narrow RF filter.
?
On 2022-10-26 02:03 PM, Richard \(Rick\) Karlquist \(N6RK\) wrote:
You can get a lot more signal out of a given loop if you tune it.
Also,?you get 9 dB additional signal every time you double
the diameter of the loop.
Do you have some requirement that prevents you from simply using a tuned loop?
On n6rk.com you can find my article on building tuned loops.
Many people have duplicated this design.
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Re: Optimizing Small Untuned Loop Antennas
One could imagine a swept receiver (wouldn't have to be SDR) that was synchronized with a swept loop antenna to make a "Panadapter" display.
Would that work for you?
toggle quoted message
Show quoted text
On 2022-10-26 16:19, Everett N4CY via groups.io wrote:
Most of us these days are using SDR receivers and want to look at a wider piece of spectrum than the small amount you will see with a tuned loop. Are we going forward, or backwards?
?
Everett N4CY
?
On Oct 26, 2022, at 6:07 PM, VE7VXO <jstreet@...> wrote:
As a bonus you also get protection from out of band signals overloading the front end of your rx by virtue of the antenna acting as a narrow RF filter.
?
On 2022-10-26 02:03 PM, Richard \(Rick\) Karlquist \(N6RK\) wrote:
You can get a lot more signal out of a given loop if you tune it.
Also,?you get 9 dB additional signal every time you double
the diameter of the loop.
Do you have some requirement that prevents you from simply using a tuned loop?
On n6rk.com you can find my article on building tuned loops.
Many people have duplicated this design.
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Re: Optimizing Small Untuned Loop Antennas
Most of us these days are using SDR receivers and want to look at a wider piece of spectrum than the small amount you will see with a tuned loop. Are we going forward, or backwards?
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On Oct 26, 2022, at 6:07 PM, VE7VXO <jstreet@...> wrote:
?
As a bonus you also get protection from out of band signals overloading the front end of your rx by virtue of the antenna acting as a narrow RF filter.
On 2022-10-26 02:03 PM, Richard \(Rick\) Karlquist \(N6RK\) wrote:
You can get a lot more signal out of a given loop if you tune it.
Also,?you get 9 dB additional signal every time you double
the diameter of the loop.
Do you have some requirement that prevents you from simply using a tuned loop?
On n6rk.com you can find my article on building tuned loops.
Many people have duplicated this design.
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Re: Optimizing Small Untuned Loop Antennas
As a bonus you also get protection from out of band signals overloading the front end of your rx by virtue of the antenna acting as a narrow RF filter.
toggle quoted message
Show quoted text
On 2022-10-26 02:03 PM, Richard \(Rick\) Karlquist \(N6RK\) wrote:
You can get a lot more signal out of a given loop if you tune it.
Also,?you get 9 dB additional signal every time you double
the diameter of the loop.
Do you have some requirement that prevents you from simply using a tuned loop?
On n6rk.com you can find my article on building tuned loops.
Many people have duplicated this design.
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Re: Optimizing Small Untuned Loop Antennas
You can get a lot more signal out of a given loop if you tune it.
Also,?you get 9 dB additional signal every time you double
the diameter of the loop.
Do you have some requirement that prevents you from simply using a tuned loop?
On n6rk.com you can find my article on building tuned loops.
Many people have duplicated this design.
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Re: Optimizing Small Untuned Loop Antennas
"Mismatch factor from 377 ohms to 50 ohms providing that the impedance of your antenna is
50 ohms."
Is this true?? I'm not sure I buy this idea.? Why should an antenna's radiation resistance match that of free space impedance and I'm not sure the theory of maximum power transfer (ie impedance matching) applies in that case.? If it did it would stand to reason that it would be equally important for a transmitting antenna as a receiving antenna.? Given that theory, then transmitting from a folded dipole (~300 ohms) should give roughly an S-unit improvement over a regular dipole (~70 ohm) on field strength measured in the far field.? I haven't measured this but I really doubt it.? By the same reasoning a magloop with radiation resistance of 20 milliohm should be down by more than 40 decibels!? This I have done, and anybody who has used a well constructed magloop and had the opportunity to compare to a reasonable dipole knows they can be quite comparable within an s-unit at the very least.? -40db would be very obvious.
Joe
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On 2022-10-26 07:24 AM, Raphael Wasserman wrote:
Hi Martin,
I see Alan has responded to the second part of your question.
I will respond to the first part regarding the antenna factor. In transmission path there are two
chains - transmit antenna - free space -receiving antenna and receiving antenna - receiver input.
There are two matching loss factors for both mentioned chains. In antenna factor is included
Mismatch factor from 377 ohms to 50 ohms providing that the impedance of your antenna is
50 ohms. Duffy’s calculator allows to change this impedance to other value. The second mismatch factor is between receiving antenna and ?receiver
Input.
Alan wrote that I mentioned passive matching between antenna and receiver input where the matching bandwidth is a couple percentage of needed broadband application.
Unfortunately, he knows only first order L matching technique. What about using band pass filters of higher order, ?or lettuce type filters?
Is he at least familiar with our member ‘s work by Chris Trask ?? Yes, it easy to shoot from the shoulder not investigating everything that is reachable regarding this topic of discussions.
Raphael
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Re: Optimizing Small Untuned Loop Antennas
Hi Martin,
I see Alan has responded to the second part of your question.
I will respond to the first part regarding the antenna factor. In transmission path there are two
chains - transmit antenna - free space -receiving antenna and receiving antenna - receiver input.
There are two matching loss factors for both mentioned chains. In antenna factor is included
Mismatch factor from 377 ohms to 50 ohms providing that the impedance of your antenna is
50 ohms. Duffy’s calculator allows to change this impedance to other value. The second mismatch factor is between receiving antenna and receiver
Input.
Alan wrote that I mentioned passive matching between antenna and receiver input where the matching bandwidth is a couple percentage of needed broadband application.
Unfortunately, he knows only first order L matching technique. What about using band pass filters of higher order, or lettuce type filters?
Is he at least familiar with our member ‘s work by Chris Trask ? Yes, it easy to shoot from the shoulder not investigating everything that is reachable regarding this topic of discussions.
Raphael
Отправлено с iPhone
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26 окт. 2022 г., в 9:47 AM, Raphael Wasserman via groups.io <wassermanr46@...> написал(а):
?Alan,
Best’s work was published in 2016 and I do not consider electrodynamics laws old fashioned.
Technologies could be new and advanced but physics theories stay the same regardless how you would slice the issues.
I see you in favor of active small loop antenna.
Would you be kind to provide me complete
Calculation scheme of active antenna not missing there broadband matching and SNR for bandwidth 30 MHz not throwing just a schematic diagram with identified components on it ?
Regards,
Raphael
Отправлено с iPhone
26 окт. 2022 г., в 9:22 AM, John KN5L <john@...> написал(а):
?Hi Martin,
EZNEC exports a Source impedance, R and X, file, LastZ.txt. SimSmith can
use LastZ.txt file for matching solutions.
System gain, or loss, is a combined EZNEC and SimSmith.
John KN5L
On 10/26/22 4:53 AM, Martin via groups.io wrote: Another issue that has puzzled me is that, if you model an antenna with
something like EZNEC and derive gain figures, does this factor in
mismatch loss or do you need to calculate this separately ?
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Re: Optimizing Small Untuned Loop Antennas
Alan,
Best’s work was published in 2016 and I do not consider electrodynamics laws old fashioned.
Technologies could be new and advanced but physics theories stay the same regardless how you would slice the issues.
I see you in favor of active small loop antenna.
Would you be kind to provide me complete
Calculation scheme of active antenna not missing there broadband matching and SNR for bandwidth 30 MHz not throwing just a schematic diagram with identified components on it ?
Regards,
Raphael
Отправлено с iPhone
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26 окт. 2022 г., в 9:22 AM, John KN5L <john@...> написал(а):
?Hi Martin,
EZNEC exports a Source impedance, R and X, file, LastZ.txt. SimSmith can
use LastZ.txt file for matching solutions.
System gain, or loss, is a combined EZNEC and SimSmith.
John KN5L
On 10/26/22 4:53 AM, Martin via groups.io wrote:
Another issue that has puzzled me is that, if you model an antenna with
something like EZNEC and derive gain figures, does this factor in
mismatch loss or do you need to calculate this separately ?
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Re: Optimizing Small Untuned Loop Antennas
Hi Martin,
EZNEC exports a Source impedance, R and X, file, LastZ.txt. SimSmith can
use LastZ.txt file for matching solutions.
System gain, or loss, is a combined EZNEC and SimSmith.
John KN5L
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On 10/26/22 4:53 AM, Martin via groups.io wrote: Another issue that has puzzled me is that, if you model an antenna with
something like EZNEC and derive gain figures, does this factor in
mismatch loss or do you need to calculate this separately ?
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Re: Optimizing Small Untuned Loop Antennas
Raphael
Dr Best's paper is a very old fashioned outline approach to
receiving antennas because it uses matching using passive
components which implies narrow band operation. It completely
omits active antennas which remove all of the matching issues and
produce true ultra wideband operation. It also omits the major
determinants such as? sensitivity to local noise fields and?
directional arrays which are key factors in antenna selection.
A passive match antenna has reciprocity- it works equally well (
or bad) for receiving and transmitting. An active antenna is
non-reciprocal as it is receive only so can break out of the
passive match constraints, mismatch loss ( which is not a real
issue anyway) is completely sidestepped.
A small ( less than resonant length) antenna? can be passively
matched? to any frequency? from VHF to VLF however the bandwidth
will never be much more than a few percent of the tuned frequency
unless the structure is very insensitive. An active 1m loop can
operate from around 10KHz to 25MHz with almost constant high
sensitivity and without any tuning. Such a loop has very
predictable and reproducible phase performance so it is
straightforward to combine arrays of antennas to produce beam
forming which can be adaptive and can drive arrays of receivers.
E-field active antenna arrays are also real, both active H and E
field antennas can be mixed and have the very significant
advantage of not having significant inter-unit coupling, a major
advantage over resonant elements where changes in one element
cause change throughout an array ( e.g. Yagi antennas , square or
circular arrays).
Regards, Alan G8LCO
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Re: Optimizing Small Untuned Loop Antennas
Hmmm,
I've always assumed that the Antenna Factor included any mismatch loss, but you may well be correct in your comment.
Another issue that has puzzled me is that, if you model an antenna with something like EZNEC and derive gain figures, does this factor in mismatch loss or do you need to calculate this separately ?
For example if I import a S parameter file into SimSmith that has been derived from EZNEC (or similar) do the losses include the antenna gain (Indication of Radiation Resistance ?) or do I need to separately derive a combined value including antenna gain from NEC and and mismatch losses from SimSmith ?
Regards,
Martin
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Re: Optimizing Small Untuned Loop Antennas
Small correction to my e-mail: ? The definitions shall be corrected – mismatch loss factor is ?expressed for these equations ( its range of value 0 to 1 ). Mismatch loss will be defined as 10 log of mismatch loss factor. So, the mismatch loss factor 1 equals to mismatch loss of 0 dB. ?
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From: [email protected] < [email protected]> On Behalf Of Raphael Wasserman via groups.io Sent: Tuesday, October 25, 2022 8:42 PM To: [email protected]Subject: [loopantennas] Optimizing Small Untuned Loop Antennas ? All,
I am wondering whether those who spend a lot of time building and testing small loop antennas besides Owen Duffy's concept of SNR degradation? are familiar as well as with Steven R. Best's research? work "Optimizing the Receiving Properties of Electrically Small HF Antennas" published in 2016 ? This article can be found on? site ?.
He describes how the mismatch loss between antenna and receiver effects receiver sensitivity and noise figure for both small dipole and magnetic loop antennas.? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? Everyone knows it is very challenging task to minimize mismatch loss factor for small receiving antenna.
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? I guess in Duffyy's concept the mismatch loss is not taken into consideration at all because he operates with Antenna Factor only where just a straight "conversion"? between free space impedance value 377 ohms ( the far zone of transmit radiation)?to receiver input impedance of 50 ohms is admitted ( that follows the a classic equation for Antenna Factor definition ).?
However, we should deal with Mismatch Loss = 4 Ra x Rl / | Za + Zl|^ 2? , where Ra - radiation resistance plus ohmic loss of loop, Rl - active resistance of receiver input, Za - antenna impedance and Zl - receiver input impedance.
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?Mismatch Loss = 1 - |Г|^2 , where?Г - reflection coefficient from receiver input can be expressed differently as well.
In other Duffy's published articles about small loop antennas I found that he neglects Ra due to a small value considering only La - antenna inductance.? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? So, there is no mismatch loss ( almost zero value) and therefore,? the reflection coefficient Г=1, meaning an open circuit...
Although in other article he ( Owen Duffy ) states the maximim received power from antenna to receiver will occur when Xa = Rl for loop antenna, where Xa -reactance of antenna caused by La inductance.?
Does it fit with ealier shown equation for the mismatch loss ?
?
Regards,
Raphael?
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Optimizing Small Untuned Loop Antennas
All,
I am wondering whether those who spend a lot of time building and testing small loop antennas besides Owen Duffy's concept of SNR degradation? are familiar as well as with Steven R. Best's research? work "Optimizing the Receiving Properties of Electrically Small HF Antennas" published in 2016 ? This article can be found on? site ?.
He describes how the mismatch loss between antenna and receiver effects receiver sensitivity and noise figure for both small dipole and magnetic loop antennas.? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? Everyone knows it is very challenging task to minimize mismatch loss factor for small receiving antenna.
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? I guess in Duffyy's concept the mismatch loss is not taken into consideration at all because he operates with Antenna Factor only where just a straight "conversion"? between free space impedance value 377 ohms ( the far zone of transmit radiation)?to receiver input impedance of 50 ohms is admitted ( that follows the a classic equation for Antenna Factor definition ).?
However, we should deal with Mismatch Loss = 4 Ra x Rl / | Za + Zl|^ 2? , where Ra - radiation resistance plus ohmic loss of loop, Rl - active resistance of receiver input, Za - antenna impedance and Zl - receiver input impedance.
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?Mismatch Loss = 1 - |Г|^2 , where?Г - reflection coefficient from receiver input can be expressed differently as well.
In other Duffy's published articles about small loop antennas I found that he neglects Ra due to a small value considering only La - antenna inductance.? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? So, there is no mismatch loss ( almost zero value) and therefore,? the reflection coefficient Г=1, meaning an open circuit...
Although in other article he ( Owen Duffy ) states the maximim received power from antenna to receiver will occur when Xa = Rl for loop antenna, where Xa -reactance of antenna caused by La inductance.?
Does it fit with ealier shown equation for the mismatch loss ?
?
Regards,
Raphael?
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Re: New to group and quest for loop… #160
Hi John, Would you share with our community how to break laws of electrodynamics and wave propagation nature to receive shortwave stations apart 6000 miles using indoor small loop antennas in USA unless your antenna is located on top of St Helen mountain?
Regards, Raphael Отправлено с iPhone
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24 окт. 2022?г., в 10:57 PM, John Perry <indianashortwave@...> написал(а):
?
I thought that congress and the FCC directed that all HOAs cannot
ban all antennas.?
Alan - W6ARH
On 10/24/2022 7:03 PM, John Perry
wrote:
I've did it relatively successfully over the years
and I've seen others do it that way as well. I know this much
and I've had plenty of 2000 to 6000 mile contacts over the years
using Magnetic Loops indoors at relatively low wattages under
100 watts. It can be done plus here in the states we have a lot
of lightning prone areas where you might not want to have your
mag loop outside and be able to use it in an attic or somewhere
that isn't so conspicuous. One problem here in the United States
is the increasingly influence of the local antenna police called
HOA or commonly known as homeowner associations. Therefore there
are many hams who cannot because of their local environment be
able to put a funky looking loop outside even on their patio or
some other place around their property even with them owning
their property that they are still subject to HOA rules due to
it being a requirement for such ownership of said property.?
Many Americans these days live in apartments as well and
some of the restrictions that come with boilerplate leases and
renting also involve restrictions on any outside antenna
including anything that would be much more than the basic
satellite dish of maximum of one meter or approximately 40
inches in diameter. Anything else is seriously prohibited in
many rental agreements or even by landlords who do not want
antennas visible in their properties. So therefore ham radio
operators and shortwave enthusiasts often have to conceal
these antennas from spying eyes or nosy neighbors or
overbearing landlords, apartment police or such ne'er do wells
that have nothing better to do than serve as the local
auxiliary police force of the local apartment complex or the
neighborhood due to the HOA.?
One can use these loops to receive signals from thousands
of miles away with quite acceptable results like my reception
daily of Radio New Zealand from 13000 kilometers or 8200 miles
away with S9 plus signal on a daily basis just using a Yaesu
FRG-100B receiver with a small 4 foot magnetic loop with quite
good results. Then again I've also used magnetic loops to
contact many stations in Europe and Russia which are both well
over 4000 miles/7000 kilometers away in the case of Europe as
well as much as 7000 miles/10000 kilometers away to Russia or
even Japan which is 10000 km away or 6000-6500 miles away.?
I've also worked a little over 100 countries using indoor
antenna such as a 200 foot longwire?ran around a ceiling and
fed into a 9 to 1 balun for a number of years as well and also
achieved a great deal of success with working long distance
DX.? I'll take my results for now and when my situation
changes in the future will probably be putting up something
outdoors but for now what I have works. I might also add that
I've also worked a great deal of these same countries with a
mobile station in my automobile over many years as well
including 6000 mile contacts to Russia on occasion when the
conditions are right.
Hi
Why anyone would want to put any antenna indoors especially a
magloop is questionable ( or unavoidable.)
It will couple to everything..needs to be? outside..especially
as 160m ( lots of electrical man made? noise.)
It can be hid though ( painted green etc) and can be close to
gnd..obviously higher 2m? Is better, but it will work say at
1m? above gnd. JUST BE sure no one can touch it while txing!!
Simon
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VE7VXO
Steven Greenfield AE7HD
Everett N4CY