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Re: Null Depth versus Torsion

 
Edited

I dont believe that faradays law (which can be used to explain the voltage induced in a small constant current loop) distinguishes between a horizontal and a vertical part of the loop conductor. Coils, and a loop can be in a simplified model assumed as a 1-turn coil, are normally circular. What would you assume in a circlar loop conductor?
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With the earlier postet EZNEC model it should be possible to calculate the currents and their phase relations.
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maybe this document helps. pages 5, 22.
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regards
Fred
Re: Wellbrook 50 ohm preamp to Files

 

Steve,
Yes, I'd like to do this comparison when I have time. Finally a reason to use 2SC5551's that you sent me a while ago :)
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Martin,
This preamp is a 50 Ohm in/out Norton push-pull, the only variation is the output transformer.
Wellbrook loop is a low input impedance and a different topology: the feedback/augmentation is part of the input transformer, and the output transformer is for differential to single ended conversion only.
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73, Mike AF7KR
Re: Wellbrook 50 ohm preamp to Files

 

It looks similar to the Wellbrook loop amplifier itself, but I think some time ago, it was decided that this wasn't actually a Norton Amplifier, but it embodied another form of augmentation.
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Regards,
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Martin
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On Tue, Oct 15, 2024 at 08:52 PM, vbifyz wrote:

I wonder how this 2-transformer circuit compares to Lankford 4-transformer design in terms of IMD
Re: Null Depth versus Torsion

 

On Tue, Oct 15, 2024 at 05:08 PM, JohnT wrote:
I'm not clear as to the meaning of your term "... H cross horizontal is still zero", please explain.
Ah, that's where I'm totally out of my depth, JohnT.
(I meant the vector cross product of H with any horizontal conductor.)
Just don't understand how a horizontally varying H vector can induce any current in the top or bottom cross-pieces.
Am I completely missing the point?
Is this where schoolboy visualisation breaks down?
Re: Wellbrook 50 ohm preamp to Files

 

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Mike,

Since you told us you have an IMD test set, maybe you should build the two types and measure them, using same transistors and same current, and let us know the results.??? :)

Steve

On 10/15/2024 1:52 PM, vbifyz via groups.io wrote:

I wonder how this 2-transformer circuit compares to Lankford 4-transformer design in terms of IMD. I would expect even better OIP2, because of the symmetry of the output transformer
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73, Mike AF7KR
Re: Wellbrook 50 ohm preamp to Files

 

I wonder how this 2-transformer circuit compares to Lankford 4-transformer design in terms of IMD. I would expect even better OIP2, because of the symmetry of the output transformer
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73, Mike AF7KR
Re: Looking for a good cheap antenna analyser

 

Hi Simon,
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I think it depends upon what you are most likely to use it for, and how careful (or careless) you tend to be with kit.
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Most of my applications are indoors, but I have used it up a tower without any problems., as it fits in my top pocket, it's easy to stow away whilst doing other things.
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I also like to be able to store and export data for off-line analysis later, and for me this is a major consideration.
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But if you want a simple-to-read instrument, with big controls, that you can use with gloves on, then maybe a basic, and more conventional, antenna analyser is a better option.
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Horses for courses...
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Regards,
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Martin
Re: Looking for a good cheap antenna analyser

 

Hi All

Thanks for inputs..

As it happens..( abit of back ground info here first. I am electrical and electronic engineer on 3 ferries very near Plymouth, also have a very good mechanical background..my immediate boss ( leading hand) has taken alot of interest into my ham radio exploit's. To which he just passed his exam and now is a ham! He just bought a nano vna and brought it into work..I like the swr plot against frequency plus obviously other features.)

However..I feel I need one, but dont think it will replace the mfj up a ladder in the rain tuning a multi band Marconi T as have added another 200m ( 1250m or so now.) or so of radials. It¡¯s just too fiddley to use with one hand, plus far too fragile.

So I think for hands on antenna tuning in field ( best swr with matching adjustments vs best resonance) the mfj is just fine..BUT for research/ planning the nano is required.

Boss¡¯s cost ?80..($90?) not too bad..

Your thoughts please..thanks.

Simon g0zen on Dartmoor, Devon
Wellbrook 50 ohm preamp to Files

 

Andrew Ikin of Wellbrook for a short time offered a version of the ALA1530LN with an additional 9 dB gain Norton preamp in the receiver coupler--this version was called the ALA1530LNP. He developed this version which used two transformers.? I've uploaded the schematic into a new folder in the Files. /g/loopantennas/files/Wellbrook%2050%20ohm%20Norton%20Preamp He used the now-discontinued ZTX 327 transistor, but any good RF transistor can be used.

73,

Steve AA7U
Re: MLA-30+, the story continues! #Small_receiving_loops_RX-only

 

On Tue, Oct 15, 2024 at 04:23 AM, Fred M wrote:
Would it be not less effort to use two well buffered X-tal Oscillators instead of an Si5351 followed by two x-tal filters?
I have that, too. The numbers achieved with that setup were slightly worse, especially F1+F2 OIP2 (+90dBm). To be honest, I didn't buffer the oscillators that well, the max levels at the DUT input are only about -13dBm for each frequency, compared to -8dBm for Si5351a+filters.
My design philosophy is "good enough is enough", Si5351a works and this is where I stopped.
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73, Mike AF7KR
Re: Null Depth versus Torsion

 

Paul,
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I'm not clear as to the meaning of your term "... H cross horizontal is still zero", please explain.? ??
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However, since a loop that is electrically-balanced to ground does not produce a response to an electric field, I would not expect the E-field to participate in the "tilted loop" response.
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Have I misinterpreted your comment regarding the source of the imbalance?
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Re: Looking for a good cheap antenna analyser

 

The terminology and menu structure of the NANOs emulates the VNAs offered by the"big boys" .? I've used these for decades and find the NANOs very easy and quite friendly to use.? Consequently, the "up-the-tower" single-port VNAs feel clunky to me.?

Dave - W?LEV


On Tue, Oct 15, 2024 at 3:33?PM JohnG3PQA via <JohnG3PQA=[email protected]> wrote:
Martin,
All agreed and very true, but Simon was enquiring about an inexpensive antenna analyser rather than test bench device using NanoVNA Saver software etc.. The now obsolete devices have various advantages and disadvantages but may be able to be picked up cheaply.
Certainly the latest NanoVNAs have good batteries, bright screens, no problem using them outside if set up correctly. It is just a shame IMHO the menu structure and terminology of the Nanos has not been better written, but it looks as if I am in the minority here. I have a NanoVNA-F but rarely use it, the Sark is better outside and VNWA excellent device for accurate 2-port shack measurements but does not have its own screen of course. Ihave not found any problems with Win11 upgrades using the auto-installation program.
John



--
Dave - W?LEV
Re: Looking for a good cheap antenna analyser

 

Hi John,
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I agreed, we all have own personal favourites for various reasons, a lot depends upon our pattern of use.
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Personally, I tend to find that I'm using my LiteVNA 64 and TinySA Ultra for more tasks than I thought I would, and a lot of my previous test kit hardly gets switched on, unless it's for a very specific purpose.
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I find I also frequently use them as signal sources, which is something I'd not expected when I bought them.
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Regards,
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Martin
Re: Looking for a good cheap antenna analyser

 

Martin,
All agreed and very true, but Simon was enquiring about an inexpensive antenna analyser rather than test bench device using NanoVNA Saver software etc.. The now obsolete devices have various advantages and disadvantages but may be able to be picked up cheaply.
Certainly the latest NanoVNAs have good batteries, bright screens, no problem using them outside if set up correctly. It is just a shame IMHO the menu structure and terminology of the Nanos has not been better written, but it looks as if I am in the minority here. I have a NanoVNA-F but rarely use it, the Sark is better outside and VNWA excellent device for accurate 2-port shack measurements but does not have its own screen of course. Ihave not found any problems with Win11 upgrades using the auto-installation program.
John
Re: MLA-30+, the story continues! #Small_receiving_loops_RX-only

 
Edited

On Mon, Oct 14, 2024 at 03:10 PM, vbifyz wrote:
My IMD bench is:
?- Si5351a generating F1=3.58 and F2=4.914MHz,? 4mA drive strength (important)
- 5-resonator xtal narrow bandpass filters, Cohn topology.
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Would it be not less effort to use two well buffered X-tal Oscillators instead of an Si5351 followed by two x-tal filters? I do it this way with a RF-2-tone generator proposed by DC4KU and are able to measure with a Siglent 3302 an IP3 up to 36 dBm without bandstop filters. To achieve a higher measuring dynamic range bandstop filters are mandatory.
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DC4KU RF-two-tone generator (pdf in german, please use a translator)
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regards
Fred
Re: Null Depth versus Torsion

 

On Tue, Oct 15, 2024 at 01:28 AM, JohnT wrote:
Does this make sense?
Good morning and thanks, JohnT :)
Would it be right to understand the source of that imbalance would be from the E component, as H cross horizontal is still zero?
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@Martin, day-dreaming eats up too much bandwidth. I really must put a sock in it.
Re: Null Depth versus Torsion

 

Hi John,
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That is assuming you are in the correct plane WRT the incident wave, and you will also have a reduction in the amplitude component, which I speculate will be -3dB when the offset is at 45 degrees, but which will subsequently be attenuated much more rapidly with further rotation, until a null is achieved at ?90 degrees.
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Regards,
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Martin
Re: Null Depth versus Torsion

 

Good evening Paul,
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Seems to me that if you were to "tilt" your square loop such that the upper horizontal leg were closer to the signal source and the lower leg were further away from the source, a phase difference would occur between the two horizontal legs which would degrade the cancellation occurring in the vertical legs and hence the depth of the null.? eg; if the sides of your loop were 0.1 lambda in length, tilting the loop by 45 degrees off-normal to Poynting vector of the incident wavefront would result in a phase difference between the two horizontal legs of 2*0.05*360deg*cos(45deg), or 25.5 degrees.? Does this make sense?
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Best Regards,
John
Re: MLA-30+, the story continues! #Small_receiving_loops_RX-only

 

No matter what your IMD setup is, you need to run the measurement bypassing the DUT first, to see the capability of the setup.
My IMD bench is:
?- Si5351a generating F1=3.58 and F2=4.914MHz,? 4mA drive strength (important)
- 5-resonator xtal narrow bandpass filters, Cohn topology. I can slightly tweak the input frequencies to hit the maximum, it moves with temperature.
- hybrid power combiner
- step attenuator
- dummy aerial if the DUT is a loop preamp (in my case it is a 1:1:1 transformer and two 25/0.5 Ohm dividers, no reactive elements, flat response, 50dB CMRR up to 30MHz)
- here is the preamp under test
- 5-inductor bandstop filter, 2.5 .. 5.5MHz. F1/F2 Attenuation is about 35..40dB. All products of interest are outside of the stop band, but I measure their attenuation anyway to correct for it during the measurement. It is about 1 .. 1.5 dB.
- 20 or 40dB fixed attenuator to bring the signals within the range of the receiver
- Airspy HF+ Discovery
- HDSDR software
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The floor (IMD detected without the DUT) is
+110dBm OIP2 at 2.24MHz (F2-F1)
+109dBm OIP2 at 8.5MHz (F2+F1)
+47dBm OIP3 at 2.24MHz (2*F1 - F2)
+39dBm OIP3 at 6.25MHz (2*F2 - F1) - this is the one which limits my measurements, I don't see it changing with LZ1AQ or other good preamp in the path. Probably limited by the Si5351a outputs cross-modulating.
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73, Mike AF7KR
Re: Null Depth versus Torsion

 

Hi Martin, thanks a lot for that.
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Let's forget about torsion for now, and keep things simple.
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My schoolboy visualisation must have terrible flaws, but goes something like this...
For simplicity, consider a square loop.
Consider only vertically polarised signals, so E is vertical and H horizontal in the plane of the wavefront.
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With a loop broadside on to the wavefront, H does effectively nothing in the horizontal arms but induces identical currents in the two verticals. Hence complete cancellation.
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Rotated 90 degrees, the horizontals are still unaffected, and verticals get *almost* the same current in each arm. Except for the tiny phase difference at front and rear. That differential accounts for PD at the feed point and is the received signal, weaker and weaker at longer wavelengths because of smaller phase difference (hence awful efficiency).
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Now, broadside on again, *tilt* the loop a little. As before, horizontals make no contribution while by symmetry the almost-verticals still have similar induced current.
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The only difference I can see is a tiny "would-be current gradient" between top and bottom of each arm - but still symmetrical. That is at odds with experiment because the null is no longer perfect (er, is that true?).
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What is dumbo here missing?
Is there some E-field contribution we need to insert into the mix?
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Very best
Paul
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