开云体育

I was always skeptical about the claim that YouLoop has impedance close to 50Ohm, or even higher.
Finally, I just connected it to my NanoVNA. The result is as expected (by me) - it is similar to the regular 2-turn loop of the same diameter. 2-3Ohm active part across the HF band, and about 1.5uH inductive reactive part? at low HF, varying greatly across the band.
My version is a DIY replica of the original, same 1m pieces of blue cable, same SMA connectors, similar 1:1 transformer.
Am I doing something wrong?
Can somebody please try this measurement with the original?

73, Mike AF7KR

If you plough through the Airspy IO group you may find an impedance plot that Youseff originally posted. You will also come across many long discussions relating to the Youloop (which I don't intend to repeat here), including contributions from several members of this group.

There is also this impedance plot of the Youloop that Steve Ratzlaff posted on that forum.

/g/airspy/attachment/37671/0/YouLoop%20Impedance%20Sweep%201%20to%20200%20MHz.jpg

Regards,

Martin

There also valuable information in Owen Duffys Blog

On Mon, Sep 26, 2022 at 12:05 PM, Fred M wrote:

There also valuable information in Owen Duffys Blog

Yes, and compare his graphs from the linked articles showing the Signal to Noise degradation in a typical residential environment.

Single turn loop terminated in 50 Ohms



Youloop terminated in 50 Ohms



The Youloop is slightly better on the lower frequencies <1MHz, but a few dB worse just about everywhere else.

Note this comparison is using the ITU residential curve as a reference.

The ITU Rural or Quiet Rural would show much, much, more signal degradation. Which emphasises the point I was trying to make about the effect of the local noise floor, and a broadband loop antenna not having sufficient gain / sensitivity and comparisons being constrained by this factor.

Regards,

Martin

>

>If you plough through the Airspy IO group you may find an impedance plot that Youseff originally posted.>You will also come across many long discussions relating to the Youloop (which I don't intend to repeat here),>including contributions from several members of this group.
>
>There is also this impedance plot of the Youloop that Steve Ratzlaff posted on that forum.
>> /g/airspy/attachment/37671/0/YouLoop%20Impedance%20Sweep%201%20to%20200%20MHz.jpg

On Mon, Sep 26, 2022 at 01:53 PM, Chris Trask - N7ZWY/WDX3HLB wrote:

That loop must be fairly large to have a self resonance at 3.386MHz.

It's the two turns and coax capacitance that contributes to it.

I have an impedance plot that was sent to me privately by the designer Youssef Touil, and it is practically the same.

I raised a concern about this on the Airspy forum, but it was discounted, and Owen Duffy later went on to explain why my thinking was incorrect.

My comment was "The main issue is that it has a massive self resonance at around 4MHz which causes a large variation in signal level and overall sensitivity across the 1-30MHz spectrum."

Owen's response.

https://owenduffy.net/blog/?p=18135

However in other posts on the Airspy forum, Youssef states that a high impedance amplifier is required and that the Airspy Discovery has a high values of input impedance on the LF bands, plus a varying input impedance on other bands due to the use of switched input filters.

I still personally believe that using a Moebius loop is an unnecessary complication, that offers no advantages, apart from appealing to the sales and marketing folks as a 'feature'.

Regards,

Martin

All,

AirSpy Youloop with 2 turns and radius about 1/2 meter constructed of two RG402 cable limbs with a copper? shield in diameter 3 mm has following parameters:
total calculated inductance that includes both loop inductance in free space and inductance of 2 turns of innner cable conductor = 8.65 uH and cable self capacitance about 190 pf ( that uses solid PTFE dielectric e=2.02 ).
The calculated self resonance frequency of untuned Airspy's shielded loop will be at 3.93 MHz. Steve Ratzlaff's posted impedance plot shows the same value of the self resonance frequency.
Also, the calculated radiation resistance? at 1 MHz is significantly less than 1 ohm ! That is typical case for small loop antennae.
?
So, AirSpy loop antenna cannot be matched to RF amplifier with input impedance of 50 ohms, it is not intended even for HI-Z amplifier.
So great mismatch creates? antenna gain is equal to the impedance mismatch factor and the gain in the practical sense is measured around -47 dB.?

The antennas inductive reactance is larger than the radiation resistance.?
I revied Owen Duffy's plot where he presented radiation resistance? and inductance reactance variations in frequency range from 0 to 10 MHz. Based on his plot the radiation resistance is in a range of 12 to 14 ohms ?!
How is that achieved ?
Also, the inductance? is significant lower about 80 nH derived from the presented plot by Duffy.
For Airspy loop antenna it is impossible to have radiation resistance values shown on that plot. Please see work of other author Ofer Aluf where he provides formula for radiation resitsance estimate, which I have used to calculated this value.
Regarding Martin's remarks that "Moebius loop is an unnecessary complication".
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?I read other user's comments where he states about the differences in performance between Moebius vs, Conventional Split Shielded Loop:
- Moebius is better below 1.1 MHz by 6 dB
- similar performance in range 1.1 - 1.3 MHz
- conventional split is better above 1.3 MHz

I could not find any performance preferences in SW bands using Airspy Youloop. I guess, since the self resonance frequency is around 3.93 MHz the antenna should perform as a short untuned whip antenna having low radiation resistance but with capacitance reactance as well.
Regards,
Raphael

I read Mr. Duffy’s blog and while I appreciate his graphs I wish he would justify why he thought the equivalent circuit which he modeled in SimSmith had anything to do with the YouLoop.

Dave W9OFA

All,

My take is on that, anyone can use SimSmith for modeling the antenna matching to RF amplifier input providing that realistic data is entered in the model.
I noticed an unrealistic radiation resistance valure of small loop antenna has been used in this model - 14.32 ohms.
I have been looking further for the existng problem finding a solution for the mismatch impedance issue. Currently Nvarcher LZ1AQ suggests similar option to AirSpy YouLoop where? RG402 cables are used but the solved, in my opinion, the
impedance mismatch issue. They are using Levko's LZ1AQ designed RF broadband amplifier. The advantage of this amplifier is the first stage of amplifier is a common base transistor.
From transistor device electronics it is known that input resistance of common base silicon transistor can be calculated: R input = 26 mV / I emmiter current flow.
The emmiter current for this design is selected 25 mA, therefore the input resistance/impedance will be about 0.01 ohms. This is a perfect match for small loop antennas !
Also, the conection of loop antenna to LZ1AQ amplifier does not require to use a balun transformer.
Nvarcher's loop antenna kit includes a simple designed switch allowing to convert loop antenna from conventional split loop to moebius.
The LZ1AQ amplifier is not included in a weaterproof housing, so it cannot be used outdoors unless it is mounted accordingly.
From LZ1AQ design it is unclear why there are used 100 pF capacitors in addition with 220 ohms resistors in parallel to each leg of loop antenna. It seems, 50 pF capacitance additionally will be added to RG402 cable capacitance creating even lower self resonace frequency unless it is copied there from the ealier designs when a small loop antenna did not included coaxial cable limbs.??
Another option would be a design of RF amplifier using in the first stage FET transistor that provides Hi-Z input but it does not create a full impedance matching.
Probaly both discussed options shall be tested in field.

On Tue, Sep 27, 2022 at 03:58 PM, Raphael Wasserman wrote:

From LZ1AQ design it is unclear why there are used 100 pF capacitors in addition with 220 ohms resistors in parallel to each leg of loop antenna.

This is to provide Low Pass Filtering of signals on frequencies higher than 30MHz, it also provides additional matching to the loop antenna on the upper HF frequencies where the loop is approaching self resonance and needs to be terminated with a higher value of impedance.

It is explained in this note, and also demonstrates why the LZ1AQ amplifier is not suited for use with the the Youloop, or any other loops that have a self resonance on a frequency lower than 30MHz.



In order to best match and track the loop source impedance to the amplifier input impedance, single turn loops of about 1m diameter should be terminated with a low impedance (<10Ohm) on low frequencies (<1MHz), medium impedance (10 to 100Ohms) on medium frequencies (1 to 20MHz) and high impedance (>100Ohms) on higher frequencies (>20MHz).

The Wellbrook, Cross Country Wireless and the LZ1AQ, are about the only commercial designs that achieve anything near to this requirement.

Regards,

Martin

Martin,

1. Thanks for the clarification of LPF circutry used in LZ1AQ amplifier design, I followed the frequency response showing an improvement at higher frequencies by using this circuit.
2. Although, I am still sceptical while reviewing AA7U submitted plot in your article regarding LZ1AQ amplifier performance related to Z [S11] parameter depending on frequency measured range.
? ? For example, the measured with network vector analyzer AA7U input impedance at 0.1 MHz was 5.12 ohms.
? ? I made quick calculations, this amplifier uses 2N2222 transistor in the common base configuration with emmiter current 25 mA, so the calculated input resistance is about 0.01 ohms, the fixed emmiter resistor 51 ohms which is in parallel
? ? with the input resistance can be neglected. Even to assume there is some capacitance reactance parallel to the input of the amplifier at this frequency with a value of 0.3 uF it is unrealistic assupmtion.
3. Now I am confused with Duffy's work either where the small loop radiation resistance is estmated/measured around 14.32 ohms seeing impossible results in AA7U work.
4. Yes, taking in consideration another component SND you showed in your article that very low input impedance of RF amplifier is not the answer but many engineers will disagree with you as well as because the? performance of 50 ohms LNA? ? ? ? will be degraded by using??umatched low impedance antenna.
5. I do not follow where you got the self resonance frequency lower than 30 MHz, at least for looop antenna consisting of RG402 cable sections it will be significantly lower 30 MHz ( around 3.9 MHz ).
6. Your wish about terminating small 1 meter loops with certain iinput impedances in respect to the operating frequency bands based on SND can be only considered when at those frequencies you would determine as well as the radiation? ? ? ? ?resistance of antenna
Is not all the work has a value like as we in engineering field frequently saying - "s---t in, s--t out" ?

Regards,
Raphael


Regards,

Hi Rapheal

I see you are interested in theory, but have you actually tried out these amps??
Easy to make, and thus try and evaluate, compare and see which works in the real world..

Just asking..also it seems you may need to read all of Chavdar’s papers on his amplifier..and there is lots of..
Ie what are the input components for?? Obvious really..

I don’t mean to offend, but all workings behind the LZ1AQ amp are all on his site..a good interesting read btw.

Simon g0zen

BTW, my calculations for the common base input of the LZ1AQ are 26mV/25mA = 1.04 ohms (not 0.01 ohms), 2X because there are 2 inputs (P-P) so 2.08 ohms. This is of course very approximate. The input impedance measured by Steve AA7U is therefore quite probably correct.?

Tom,

Thanks for your correction finding a gross error in my calculations. Yes, it shall be 1.04 ohms. Also, I found another source by John VE6E4 that published his plot comparing three apmlifiers LZ1AQ, G8CQX and Wellgood.
L1Z1AQ provides lowest flat broadband input impedance around 1.5 to 3 ohms. So it coincides with Steve AA7U work.
Meantime I am reviewing Velkov's LZ1AQ article about SML (small magnetic loops ) where he writes that the load on small loops antenna shall be at least an order of magnitude smaller than the inductive reactance of the loop Zin << XL, where
the radiation resistance is not considered at all.

Have a great day,
Raphael

Hi Simon,

I am not in Consumer Test Business testing all amplifiers designed for active antennae.
However, I have by training and schooling an acknowledge by looking at schematic diagram and having on hands available data sheets to weigh whether that electronic device was designed for proper application.
For example, I bought Nooelec Lana HF amplifier thinking that this device with 50 ohms input will be an appropriate device for AirSpy Youloop-2t.
Later I learned it was not so...Of course, I am not interested to invest in purchasing Vector Network Analyzer? retesting all available work done by others.
Another good example I only recently started of using SDR.
I purchased a chineese maded Dongy type SDR with White Dolphin trade mark on it which was advertised as inexpensive but well performing. By reverse engineering I discovered that chineese "experts" copied someone's design but
installed solid-state switches for pre-selector filters that could not be switched on/off because of wrong logic signals beinge applied from processor to those switches. I could cut on PCB certain paths fixing the problem or switching over other available in trade switches. Instead I? decided to turn back the SDR to the vendor buying? SDR RSP1A with AirSpy Loop Antenna experiencing a new headacke with the loop antenna.

Regards,

(retired telecommunications engineer )
Raphael
?

--

Quite agree with Dave.

Here in London they are good, ie best i can do, but I can’t put up full size antennas and the noise floor here is at best bad.

However hopefully moving to a much quieter area soon.. and with much more space..then up go some more sizeable antennas for tx and rx.
( though i may try a phased set of 3 loops..or short verticals..)
Simon

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

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.