I enjoyed reading your article published in 2008 about wideband loop matching using cascaded balanaced>symmetrical lattice network where were cascaded together two first order lattices.?

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>My understanding is this network matched a real small loop antenna with its low radiation plus ohmic resistance>and loop inductance impedancee to 50 ohms active load.
>I am interested to have a reference to a scientific calculator of lattice network elements. How to calculate as>well as the decoupling ratio between loop antenna as a source and amplifier input as a load ?>You may have to resort to writing your own, starting with older texts on passive network synthesis. I had to do this about 30 years ago for the the design of group delay equalisers. Took me three months of concentrated effort.

Hi Chris,

I enjoyed reading your article published in 2008 about wideband loop matching using cascaded balanaced symmetrical lattice network where were cascaded together two first order lattices.?
My understanding is this network matched a real small loop antenna with its low radiation plus ohmic resistance and loop inductance impedancee to 50 ohms active load.
I am interested to have a reference to a scientific calculator of lattice network elements. How to calculate as well as the decoupling ratio between loop antenna as a source and amplifier input as a load ??

Regards,

Raphael

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Jerry, I used a 1788, chose it over the 1786 because 40 is very active and 10 is under used. Seems I can hear many FT8 signals, tons of CB stations a bit lower and nothing at all on 10CW or SSB.?
GeorgeC W2DB

Thanks, Mike.? I have a lot of loopiness to learn, although some already suggest I'm an expert (at loopiness).

Martin,

The misconseption with Duffy's concept cleared up when I re-wrote his quation differently as:

SND= 10log S / N ext. - 10 log S/ ( Nint + N ext) instead of his final convertion as? SND = 10 log ( N int / N ext + 1 ).

Both equation are mathematically right but the first equation is a better presentation of his concept to understand the logical meaning of SND, likewise we in our business using SINAD knowing we can compare betwen SNR without distortion vs. SNR with a signal distortion and that will?present SNR degradation as difference between both values expressed in dB.

Now I am breaking my brains to find a solution by creating a matching compensation network between Airspy Loop and mine 50 ohms LNA.? My amplifier uses MMIC Darlington amplifier GALI 39 where his input is not designed to see low source impedance/resistance from an antenna. Probably I will use a simplystic T-match LPF like Levko, LZ1AQ did between loop antenna and his balanced common base amplifier. In my case it will be an unbalanced design but using balun between antenna and LPF.The downside in this method it uses one frequency of interest in the calculations of elements vs. more sofisticated matching circuits that use BPF with more L and C elements based on few frequencies.

Have a nice day,
Raphael

Hi Raphael,

Signal to noise degradation (SND) is a concept that was suggested by Owen Duffy.



It is a mechanism that can be used in order to determine if a receive system (including the antenna) is good enough to detect the weakest of signals relative to the system noise floor.

In turn this can be used to compare the receive performance relative to the ITU defined noise curves for particular locations.

This is useful, because it provides a means of assessing if a receive system is likely to be adequate when being used in a particular environment.

The idea is that the system should have sufficient sensitivity that the weakest received signals are only degraded by 1dB by the receive system when used under conditions defined by the ITU noise curves. It provides a value to aim for when designing a system, and makes allowance for the operating conditions and frequencies.

Using these figures and the calculators provided by Owen it is possible to determine if an antenna such as a small loop has sufficient sensitivity to only be constrained by the local noise floor. Obviously the noise floor in real life will vary from location to location, but by using the ITU noise curves as a reference point, you can at least estimate what sort of performance is likely to be obtained. The larger the value of SND the greater the received signals are degraded.

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I do not have figures for shielded loop antennas. I have experimented with many, but I have not been able to find any that seem to offer any advantages over a single unshielded loop. The problem being the additional capacitance that the shielding adds, which in turn lowers the loops self resonant frequency. If the loop amplifier is well balanced, and has a low enough value of input impedance, it will have a sufficiently high value of common mode rejection, and a screen is not required.

Fat low inductance loop(s) are the best option for small broadband loop antennas.

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The self resonant frequency is more of an issue in terms of managing the input impedance of the amplifier than the actual performance of the loop. The loop will still perform in some form on frequencies above the self resonant point, but it's difficult to? manage the impedance excursions if they are in the middle of the frequency range of interest, rather than just at one end. It's convenient to have the self resonant frequency just above 30MHz, as the loop remains inductive on lower frequencies and it can be easily matched to the amplifier across the required frequency range just by using a simple L/C/R network.

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I'm not claiming to know everything about this, my maths is pretty poor and most of my comments are based on observations and experiments that I have designed and made in order to test various theories, and try to better understand how things work.

Owen Duffy's notes and email exchanges have helped me enormously in this respect, and I appreciate the effort he has gone to in order to try and 'debunk' many of the myths and incorrect information that abounds (on the web in particular). It's particuarly interesting when he tries to reconcile actual measurements with modelled figures, which very few other people bother to do (or have the skill to be able to do it).

Regards,

Martin

Hi John

Yes i agree..not so sure about using inside though.

Check my qrz.com g0zen

Not quite sure what you're trying to say with the bulk of your comment - you seem to be mixing terms yourself e.g. SNR/SND/SDR - but I'm pretty sure this Owen Duffy is the guy who used to be in the radio engineering dept at Australia's OTC (and, if I recall correctly, after OTC was sold/disbanded, ended up at the Telstra Research Labs?). I only spoke with him a few times (my area at Telecom/Telstra had some minor responsibility for a couple of weird and wonderful HF & VHF links/systems), and it's many years ago now, but he stuck in my mind as one very smart cookie with an almost weirdly-natural grasp of radio engineering theory and practice.

Over the last couple of decades I've read both his old and new blogs on and off, and while I can't say I always agree with (or even necessarily completely understand!) his posts/explanations/arguments, I usually can't completely disagree with them.

Sometimes the minimum coupling to the prevalent local interference source can be achieved by tilting the loop, so it is at some inbetween orientation for the best SNR. Usually still fairly close to vertical.
In my experience, nulling out interfering distant stations on MW or SW doesn't require tilting the loop, the best null is always with the loop being vertical.
This is relevant to RX only loops, I can not say much about benefits of tilting TX loops.

73, Mike AF7KR

Hi Martin,

Since I am new on this site I decided to spend some time finding out who is Mr. Owen Duffy,? VK20MD whom you have been frequently referencing regarding SND evaluation of loop antennae.
Is he australian HAM amateur representing National Association for Amateur Radio in Australia and a good practioner in radio field ?
I am honestly feel uncomfortably with introducing SDR concept. Why ?
The introduced equation is SND (S/N degradation ) = 10log ( N int. /N ext. + 1 ).? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? So basically, when N ext. >> N int. the SND ---> to 0 dB and when N ext. << N int.? the SND? exceeds greatly 0 dB value ( I considered? extreme conditions only for a better? comparision between both values
ambient electrical noise vs. internal amplifier noise levels to understand? the SND concept). Was it introduced by Owen Duffy or others ? What value of SDR expressed in dB would be better ?
When we deal with SNR concept, it is clear for everyone - higher value is better.?
By the way, Owen Duffy in 2012 had a presentation? "Noise and Receivers"? where he does not mention anything about SDR. Is it widely accepted by scientific and rado engineering media ?
In his presentation he wrote interesting thing that we discussed earlier: "MDS - minimum discernable signal - misleading term ( is it? possible to copy CW well below MDS )"
Later? I looked at the various plots which you presented in your published article "Broadband Loops " that shows different plots as SND= f ( d, Z inp, F ) where d - diameter of loop conductor, Z inp. - input impedance of amplifiers as a load for antenna loops and F -?frequnecy of interest.
All the work is for unshielded small loop antennas. Do you have for illustration purpose a plot for conventonal shielded loops as well, say with conductor diameter of 1 mm ?? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? Let's Let's forget about Moebius antennas because they perform well only below about 1 MHz.
I am asking about shielded loop antennas because there is introduced another unknown? factor - self resonance frequency, say between 0.1 and 30 MHz range.
I guess, in range of 0.1 MHz up to the? self resonance frequency value your published plots can be considered for shielded loops because the inductive reactance of antenna will prevail.?
What results will you predict above a self resonance frequency up to 30 MHz where capacitance reactance of antenna will prevail? over inductive reactance of antenna impedance?
Your response would be greatly appreciated.


Regards,

Raphael

Sorry I guess I misunderstood. As you talk abt EmComms 1st thing that came in my mind was: NVIS radiation patterns. And this prop mode is ok below 14MHz or so.

Anyway 10m is easy to solve as other fellows already proposed.

One last note, and may be this comment is shared by other manufacturers: on MFJ loop all joints are welded: butterfly capacitor plates, capacitor connection to the loop, etc. No screws and nuts to worry about. At least at the 1995 production =:D

Regards
Marcus

Em 28/09/2022 12:17, gfmucci via groups.io escreveu:

Hi, Jerry.?

40m hands down..10m hardly open, 40 always ( nearly) for local ish ragchews and if lucky dx..

A 10m antenna is so easy to make and hide..( use cb mobile whip,1/4w etc)

Simon

I've read about the two different orientations of loop antennas:? either vertical or horizontal.

What happens inbetween those two extremes for transmit or receive? Are inbetween orientations useful for anything?

40 meter is not mandatory. I guess my question is which is "nicer to have", 40 meters or 10 meters? I guess for me the question is is it worth rigging up a separate antenna for 10 meters to get the loop that goes to 40 - or just get the 10 to 30 meter loop version and be done with it.

开云体育

If 40m is mandatory and u are involved in local EmComms use the 1788. I have a 1786 since 1995 and actually I have a single element delta loop on 10. I use the loop on 30 ... 12m, installed at H pol. But if comparing signals on 10, the delta loop is at least a "S unit" better. Both are at the same height above my home (~6m). Yes, they are vy sharp, and on the lower bands sometimes I need to readjust after a few hours. On contests is a bit inefficient due to frequent re-tune when changing band or even frequencies inside the same band.

I remember the manual / advertisements on late 90s where they say the 1786 should perform as a dipole at the same height on 30MHz and -6dB at 10MHz. At that time I consider the Isoloop as well.

73
Marcus PY2PLL = PY3CRX

40m is more useful, so personally I'd choose that option.

You can build a wire dipole(s) or use a retuned CB antenna on the upper HF bands (including 10m) and it will be more efficient than a small loop.

Regards,

Martin