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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

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 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
?

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

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.?

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

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,

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

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.

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,

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

One paper on this subject here :



Xtian

The paper "Resonant Power Conversion through a Saturable Reactor" is very interesting.

If you find anything else on the subject I would be very grateful.

Tthank you very much to all.

Fernando Martin

The article compares the distortion of a saturable inductor with
a single varactor. This is the proverbial "straw man" comparison,
since anyone who cares about distortion uses a pair of varactors
in series/opposed. Surely Chris knows this. Also, there is
no discussion about the Q of the transductor.

Rick N6RK

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

Martin,
As you know antennae are used not only for SDR but for any designed receivers, thus practically
would be better to specify sensitivity not as MDS.
By the way, it makes sense to use MDS when an operator on video display desires to acknowledge a carrier signal that has SNR=3db but we are not
In radar target acknowledgement business.
We are interested to demodulate the rf signal and listen to it’s content.
Regarding your point what would be better to specify sensitivity in power terms vs. voltage.
In our rf engineering business has been accepted
For UHF bands to specify in power units but for lesser carrier frequencies in voltage units.
Any engineer knows how to convert not forgetting to specify the needed impedance value of the load.
You brought up another interesting point when measured in voltage units gets that specified as potential difference or otherwise.
In my opinion, it is irrelevant because from schematic diagram or any other source engineer knows what is included in his design equation.
Regards,
Raphael

>

>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