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FW: [loopantennas] Optimizing Small Untuned Loop Antennas

Raphael Wasserman All Messages By This Member #16893 开云体育 Good evening Martin, ? I found for you a paper published by Duffy at his blog Please read this article especially at its end where he points out about 0.08 % ?efficiency of small loop. Probably now you may understand the meaning of receiving antenna efficiency factor. ? Good luck, ? Raphael ? toggle quoted message Show quoted text From: [email protected] <[email protected]> On Behalf Of Raphael Wasserman via groups.io Sent: Sunday, October 30, 2022 12:18 PM To: [email protected] Subject: Re: [loopantennas] Optimizing Small Untuned Loop Antennas ? Hi Martin, 1. I was interested to know how works Duffy's published calculator for small loops. Of course, all intermediate steps of calculations with this device were unknown for me but Duffy did mention the reference source ? ? which he used to create a calculation program. I was eager to verify the results using known equitions that are published widely in various technical literature sources. 2. The Gain of antenna is defined through an equation: ? ? ?Ga = 10log 4pi +10log K +10log D + 10log A -20log wavelength of interest, the meaning of? ? parameters you can find in my previous emails. 3.? The efficiency of antenna K is a ratio of radiation resistance to sum of radiation rasistance and ohmic loss of antenna. ? ? ?So, I used R rad= 0.01 ohm and R ohmic resistance=1 ohm, just for a sake of argument for small loop antenna. The K is about 0.01? ( or 1% ), or 10log 0.01= -20 dB ? ? ?Of course, you can use other values to calculate K on your own. ? ? ?In addition, that is true for a? tuned antenna regarding the antenna efficiency factor. 4.? Now regarding any advantage or disadvantage between untuned and tuned small loop antennas using your words - outperforming. ? ? ?Yes, there is an advantage of tuned antenna due to the Q-factor that multiplies accordingly the received signal because ? ? ?Vo=E/AF and Usig=Vo x Q at receiver input when it is a condition of parallel resonance. ? ? ?Many sources say the advantage between tuned and untuned small loop antennas could be expected by 6-10 dB due to the Q-factor. ? ? ?However, we have to take everything in a proper way, considering as well as the presence of ambient noise that will be equally multiplied by the Q-factor ( Unoise ambient x Q ). ? ? ?So, the SNR will not be improved at receiver output unless the ambient noise is significantly less than the thermal noise of your receiver and we can consider only the presence of thermal Johnson noise. ? ? ?Let's take an extreme case when the direction of desired received signal and ambient noise are the same and you cannot minimize with your directional loop antenna... Regards, Raphael?? ? ? ? ? ? ?
vbifyz All Messages By This Member #16894 Rafael, The article is about a shielded tuned loop with a split capacitor matching to 50 Ohm. 30dB loss on 7MHz compared to a full size dipole is not bad at all for a receive only antenna. Maybe a problem for a quietest of locations - see my comment below on that. Transmit is a different story, but I am not aware of people using shielded loops and split capacitor matching for TX. I don't think parameters like loop efficiency and loop mismatch loss are suited to compare small loop RX antennas. Personally, I like parameters Chavdar LZ1AQ uses in his work on small active loops: the antenna factor (the ratio of the preamp output to the field strength, 1/m units) and the noise floor expressed in field strength units (uV/m). Very intuitive. Then there is the main reason we use loop antennas for RX - a deep null allowing to minimize some interference (local or DX). In the city and suburbs it improves the signal-to-interference ratio, and allows hearing signals which can not be heard with wire antennas. In quiet rural locations there is no such reason, and there is usually more room available, so small loops are not the optimal solution. If you don't like the poor antenna factor and low efficiency of a small loop, just use a full size wire. If you are in a quiet but space constrained area, then a short active vertical may be a better solution, because of its higher antenna factor (compared to both wires and loops)? and lower uV/m noise floor (compared to an active loop). 73, Mike AF7KR
Simon All Messages By This Member #16900 Check my qrz.com
Martin - Southwest UK All Messages By This Member #16902 On Sun, Oct 30, 2022 at 10:51 PM, Raphael Wasserman wrote: Probably now you may understand the meaning of receiving antenna efficiency factor. Unfortunately, I'm now even more confused... But it think this is simply due to the definitions and how they are being used. A quick question. If we have a 'broadband' un-tuned loop, and then tune it to resonance, does this change the Radiation Resistance ? Regards, Martin
Raphael Wasserman All Messages By This Member #16904 开云体育 Martin, ? Regardless the type of loop antenna untuned or tuned the radiation resistance gets calculated ?the same way because the radiation resistance is: ??? R rad.= 31200 x (NxA / wavelength of interest^2) ^2 where N – number of loops, A=pi x ( D/2)^2 ,where D is diameter of loop. Only the deference between an untuned and tuned loop antennas will be their impedances due to Q-factor of antenna at resonant frequency. ? Regards, ? Raphael ? toggle quoted message Show quoted text From: [email protected] <[email protected]> On Behalf Of Martin via groups.io Sent: Tuesday, November 1, 2022 12:11 PM To: [email protected] Subject: Re: FW: [loopantennas] Optimizing Small Untuned Loop Antennas ? On Sun, Oct 30, 2022 at 10:51 PM, Raphael Wasserman wrote: Probably now you may understand the meaning of receiving antenna efficiency factor. Unfortunately, I'm now even more confused... But it think this is simply due to the definitions and how they are being used. A quick question. If we have a 'broadband' un-tuned loop, and then tune it to resonance, does this change the Radiation Resistance ? Regards, Martin

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