Re: Null Depth versus Torsion
Hi Jim,
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A mate of mine, Ron, G4GXO, still produces cave radios, using different sized loop antennas, and operating on frequencies below 100kHz, using DSP and Class E PA's.
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They have been used on many successful explorations of major deep level cave systems, and have helped to map and link passageways from previously separate systems.
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Some videos, for when you have some "downtime".
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Regards,
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Martin
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On Wed, Oct 16, 2024 at 08:54 PM, James Redding WA9VEZ wrote:
In the late 1980's, below the soil surface, there was a lot of experimentation with "cave radios" using loop antennas at 200+ meter depths. RF does penetrate through "earth".
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Re: Null Depth versus Torsion
On Wed, Oct 16, 2024 at 03:47 PM, JohnT wrote:
Does this make sense??
Yes a lot, John, many thanks.
And I still prefer "tilt" to "elevation" (height above ground to "normal" people) ho ho ho.
James' post is most interesting too.
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Of course, fine tilt adjustment for a better null is a big DIY ask.
And skywave propagation wrecks any kind of stability.
So it's all a bit academic. But great fun.
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Re: Null Depth versus Torsion
Thank you John, for your explanation.
And yes, your consideration makes sense for me. I haven't yet spent some thougts on that issue but i find it very interesting and challenging to follwo the discussion.
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regards, Fred
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Re: Wellbrook 50 ohm preamp to Files
I have the Ilkin-Norton preamp built, using 2SC5551 transistors, 9dB version. There are some minor deviations from the original, the biggest one being bigger BN73-202 cores used (this is what I have on hand).
Got the transformer windings right the first time, no oscillations and a nice 9dB gain, rolling off to 7.5dB at 30MHz (maybe because of the oversized transformers and the 73 material). -3dB point is around 35MHz. No measurable rolloff on the low end to at least 100kHz (NanoVNA limit).
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My IMD setup is finicky after laying on the shelf for more than a year, need to spend some more time to get reliable numbers out of it. I can already see that IP3 is good, but IP2 is not what I expected from a symmetrical design (worse than a push-pull resistive feedback preamp I compared it with). Surprisingly, the optimum current (lowest IMD) is not the highest I tried, ~40ma per transistor, but somewhere around 15mA per transistor. Is this a known 2SC5551 property? Ferrite bead saturation maybe?
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More numbers to follow after I completely revive and recalibrate my IMD bench.
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73, Mike AF7KR
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Re: Tell my why I need a VNA?
Dave
Thank you I kind of suspected this¡
Tom
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Tom Anderson
SDR_Radio@...
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On Oct 16, 2024, at 12:33?PM, W0LEV <davearea51a@...> wrote:
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For receiving only, and I'll be blunt, you probably don't need a VNA or spectrum analyzer.?
HOWEVER, if you do filters of any kind, you must measure the Ls and Cs to assure the filter will work as designed.? Then finally to measure the filter to verify the design.? Both require a VNA or a spectrum analyzer with a tracking generator which amounts to
a scalar network analyzer.???
Dave - W?LEV
I would say that if all you are designing are passive non-resonant antennas then a VNA may not be all that useful.
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However, if you are designing resonant antennas or any sort of filter then a VNA is essential. For resonant antennas the best way to tell where they are resonant is with a VNA. Filters, especially ones where you are winding toroids for inductors need to
be tweaked to get best performance, and a VNA is the best tool for that.
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For active antennas it could be argued that a spectrum analyzer is better. It is if you want to do IMD measurements.
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As inexpensive as the NanoVNA and TinySA I would get both if you can afford them. Make sure you buy the "real" versions and not clones if you do. There are groups for both and resources to find a source for the "real' units.
--
===================================================================
Mike M
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Re: Null Depth versus Torsion
The graduate students at Ohio State, "discovered" several abandoned pipes underneath the athletic field that were distorting their expected RF field strength measurements on the surface. . .
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Unless you have recent data of the "ground" conductivity underneath an "antenna", you can never really be sure about the "air side" measurements. Soil conductivity varies with frequency ( ("skin effect"), soil moisture ("rain"), soil composition (rocks), and chemistry, to name a few.
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The whole linear idea of "H" and "V" polarization is pretty much a mental shortcut. The more realistic, mathematically exact (but annoyingly complex), characterization of EM waves is the idea of? the Poynting vector which is "energy" per unit area. It is the cross product of B X E . the "X" is the vector cross product and not "multiplication".
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An immediate demonstration is the angled signal null observable with an AM portable radio. To obtain a null, the antenna ferrite rod must be slightly tilted off vertical for maximum carrier null.
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The angle of the null is named as "wave tilt" in the literature. (Zenneck, 1907).
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Auf Deutsch:
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ZENNECK J., 1907. - Uber die Fortflanzung ebner electromagnetischer Wellen
einer ebenen Letterflache und ilire beziehung zur drahtlosen telegrapie. ? Ann. Phys. ?. Series 4, 23, p. 846-850.?
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. . . to quote a more recent work that is accessible off the web:
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The study of amplitude and phase of wave-tilt of TE and TM-mode have been carried out. The amplitude and phase of
wave-tilt of TE-mode waves have been found to vary significantly with various parameters of the earth's subsurface. The amplitude and phase of wave-tilt of TE-mode maximise and vary rapidly in the lower frequency region, whereas for TM-mode wave is known to maximise and change rapidly in the higher frequency region . . .
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In the late 1980's, below the soil surface, there was a lot of experimentation with "cave radios" using loop antennas at 200+ meter depths. RF does penetrate through "earth".
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? ? ? ?about page 10. . .?
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JIm/VEZ
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Re: Looking for a good cheap antenna analyser
Hi Simon,
Thanks for providing the consolidated info. My nano VNA is several years old. I need to compare it with the currently available units.
Mine is a NanoVHA-H4.
Regards
Clint
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-----Original Message----- From: [email protected] [mailto: [email protected]] On Behalf Of rfsam via groups.io Sent: Wednesday, October 16, 2024 9:00 AM To: [email protected]Subject: Re: [loopantennas] Looking for a good cheap antenna analyser Here is my personal list. 1. I really like NanoVNA-F that was originally designed by Deepelec. Metal case, big screen, big battery. Cost is around $100. Here is a link to their Aliexpress store: They also sell TinySA Ultra and more stuff and it's a legit place to buy from. NanoVNA-F: Their "newer" DeepVNA. Not sure what's the difference between "F" and "Deep": 2. NanoVNA-F v2. V2 version of "F" was designed by sysjoint.com. Can be purchased from a few places (Aliexpress and Amazon). This Amazon store is often mentioned: Not sure how better is V2 F compared to the original F, but it's slightly more expensive. 3. If you really want to spend around $300 or more then I'd probably get a V2 from here: Either v2Plus4 model or more expensive v2Plus5 But to be honest for what I do with VNAs at home my original "F" works very well! But I have an access to Big Box VNAs at work. Maybe I'd get #3 from my list if I didn't. Regards, Simon On Wed, Oct 16, 2024 at 3:39?AM Martin - Southwest UK via groups.io <martin_ehrenfried@...> wrote:
There are lots of fakes and poor performing clones out there, I bought mine directly from the approved Zeenko store on AliExpress.
But other dealers include Mirfield Electronics in the UK, but not all types are available.
Regards,
Martin
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Hi Martin, I agree with everything you said! As I just recently started using HAM/Hobbysist stuff and pretty much my entire career I'm using professional equipment. Also yes, HF maybe harder then higher frequencies because of components size and etc. For example on VHF/UHF and higher I can use simple microstrip based combiners that don't have ferrites inside and their own limits are high. You can even use simple directional couplers for combining (just use uneven tone power to compensate for coupling coefficients). So, I maybe a bit biased here based on the equipment and frequency ranges I use at work. Sorry if my information was confusing! Thank you! On Mon, Oct 14, 2024 at 1:30?PM Martin - Southwest UK via groups.io <martin_ehrenfried@...> wrote:
Hi Simon,
Mabe it's possible with later generation analysers that have a greater dynamic range, but most stuff available to hobby users isn't going to cut it.
I have a HP8563E, but it hardly gets turned on, as apart from the frequency coverage to 26GHz, it's not that much use for everyday stuff.
My tone sources are two crystal oscillators followed PA's and then by attenuators, individual absorptive band pass filters, a high power combiner and yet another attenuator, all built into a standalone box. I start off with 5w of RF and end up with 100mW at the output. The mini-Circuits combiners that are normally specified start to generate their own IP's at around +10dBm, and standard band pass filters don't present a 50 ohm match outside their passband, which can affect the generation of IMD products.
Even with this, and a decent set of notch filters, I have difficulty making repeatable IMD measurements, mainly because of leakage and minor phase shifts that affect the generation of IMD. It's hard enough at HF frequencies, and having in the past measured passive IMD, produced in cellular antennas, I know how much more difficult that can be.
You read the application notes from folks like Aligent / Keysight, and they make the test setup it looks easy, but at least for me, in a home workshop, it wasn't that straight forward.
However, I'm prepared to accept that your mileage may vary...
Regards,
Martin
On Mon, Oct 14, 2024 at 06:29 PM, rfsam wrote:
One just need a good "Big Box" Spectrum Analyzer (HP/Agilent/Keysight) with good LowPIM attenuator in front of it.
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Re: Tell my why I need a VNA?
For receiving only, and I'll be blunt, you probably don't need a VNA or spectrum analyzer.?
HOWEVER, if you do filters of any kind, you must measure the Ls and Cs to assure the filter will work as designed.? Then finally to measure the filter to verify the design.? Both require a VNA or a spectrum analyzer with a tracking generator which amounts to a scalar network analyzer.???
Dave - W?LEV
I would say that if all you are designing are passive non-resonant antennas then a VNA may not be all that useful.
?
However, if you are designing resonant antennas or any sort of filter then a VNA is essential. For resonant antennas the best way to tell where they are resonant is with a VNA. Filters, especially ones where you are winding toroids for inductors need to be tweaked to get best performance, and a VNA is the best tool for that.
?
For active antennas it could be argued that a spectrum analyzer is better. It is if you want to do IMD measurements.
?
As inexpensive as the NanoVNA and TinySA I would get both if you can afford them. Make sure you buy the "real" versions and not clones if you do. There are groups for both and resources to find a source for the "real' units.
--
===================================================================
Mike M
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Re: Tell my why I need a VNA?
I would say that if all you are designing are passive non-resonant antennas then a VNA may not be all that useful.
?
However, if you are designing resonant antennas or any sort of filter then a VNA is essential. For resonant antennas the best way to tell where they are resonant is with a VNA. Filters, especially ones where you are winding toroids for inductors need to be tweaked to get best performance, and a VNA is the best tool for that.
?
For active antennas it could be argued that a spectrum analyzer is better. It is if you want to do IMD measurements.
?
As inexpensive as the NanoVNA and TinySA I would get both if you can afford them. Make sure you buy the "real" versions and not clones if you do. There are groups for both and resources to find a source for the "real' units.
--
===================================================================
Mike M
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Tell my why I need a VNA?
Good day all,
Help me out¡ I am only interested in reception of signals from DC to Daylight with SDR radios in my urban environment, (Not interested in transmitting.) ?I am also an active antenna tinker (like to build things and try them out) my theory has been toss some wire and metal together and see if it works. ??
A bit of background. I study and used Smith charts 40 years ago, heck I can not tell you what they even do anymore. ?I have a very good understanding of radio and a basic idea of antenna Theory (I understand SWR and wave lengths know how a dipole works etc) However, I am over my deep theory days. ?So please in basic terms tell me why I should have an Antenna Analyzer? ?What will it do for me? ?How can it help in building the antenna that can hear a big pass gas at 1000 Km away.
I have a little extra pocket money and if I can be sold on the idea of a VNA I could get one. ?But my ignorance is stopping me..
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Thank you for your time.
Tom
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Re: Looking for a good cheap antenna analyser
Yes, looks like Zeenko is another good place to buy from aside from Deepelec and a store on Amazon. Thank you, Simon On Wed, Oct 16, 2024 at 3:39?AM Martin - Southwest UK via groups.io <martin_ehrenfried@...> wrote:
There are lots of fakes and poor performing clones out there, I bought mine directly from the approved Zeenko store on AliExpress.
But other dealers include Mirfield Electronics in the UK, but not all types are available.
Regards,
Martin
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Re: Looking for a good cheap antenna analyser
Here is my personal list. 1. I really like NanoVNA-F that was originally designed by Deepelec. Metal case, big screen, big battery. Cost is around $100. Here is a link to their Aliexpress store: They also sell TinySA Ultra and more stuff and it's a legit place to buy from. NanoVNA-F: Their "newer" DeepVNA. Not sure what's the difference between "F" and "Deep": 2. NanoVNA-F v2. V2 version of "F" was designed by sysjoint.com. Can be purchased from a few places (Aliexpress and Amazon). This Amazon store is often mentioned: Not sure how better is V2 F compared to the original F, but it's slightly more expensive. 3. If you really want to spend around $300 or more then I'd probably get a V2 from here: Either v2Plus4 model or more expensive v2Plus5 But to be honest for what I do with VNAs at home my original "F" works very well! But I have an access to Big Box VNAs at work. Maybe I'd get #3 from my list if I didn't. Regards, Simon On Wed, Oct 16, 2024 at 3:39?AM Martin - Southwest UK via groups.io <martin_ehrenfried@...> wrote:
There are lots of fakes and poor performing clones out there, I bought mine directly from the approved Zeenko store on AliExpress.
But other dealers include Mirfield Electronics in the UK, but not all types are available.
Regards,
Martin
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Re: Null Depth versus Torsion
Paul,
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I too am operating from a schoolboy visualization (as viewed through an often-faulty memory!).? My mental model invokes Ampere's law of induction relating the total EMF produced by a loop immersed in a magnetic field to the time-rate-of-change of magnetic flux passing through the loop.? We can express the total EMF as the sum of the EMFs produced by the four legs of the square loop.
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Assume that the loop lies in a plane perpendicular to the Poynting vector, i.e. no "tilt".??As the incident radiation was specified as being circularly polarized, the plane in which the radiation E and H components lie itself may be seen as rotating about the Poynting vector.? ?At those times when the magnetic vector of the incident radiation is horizontal, the EMFs produced by the two horizontal legs will be zero as you had pointed out in your recent post, but at all other times when the H vector has rotated such that it is not horizontal, the EMFs produced by the two horizontal legs will be non-zero and equal but with different signs.? Consequently, the two EMFs will cancel.? The same situation is present at the two vertical legs, but the zero-EMF instances are displaced by a 1/4 of the radiation's period.? The net effect is a zero-EMF around the loop.
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If we now "tilt" the loop such that the upper horizontal leg is closer to the radiation source and the lower leg further away we introduce a phase difference between the H vector present at the upper and lower horizontal legs resulting in a difference between the EMF's produced by the two legs.? This will sum with any difference in the EMF's produced by the two vertical legs resulting from rotation of the loop in azimuth.? Assuming that the amount of "tilt" introduced is small, the impact of the small "tilt" EMF produced by the horizontal legs will be much more evident at azimuth angles corresponding to nulls, where the net EMF produced by the two vertical legs is also small.
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Another way to express this situation is that due to the radiation's circular polarization, the EMF contributions from the "horizontal" legs of the loop to changes in loop elevation are identical to? those of the "vertical" legs to changes in loop azimuth, only displaced in time by 1/4 of the radiation's period.? For the loop to produce its deepest null, the normal vector to the plane of the loop must be made colinear with the Poynting vector of the incident radiation.
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Does this make sense??
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JohnT
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Re: Looking for a good cheap antenna analyser
There are lots of fakes and poor performing clones out there, I bought mine directly from the approved Zeenko store on AliExpress.
?
But other dealers include Mirfield Electronics in the UK, but not all types are available.
?
?
Regards,
?
Martin
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Re: Looking for a good cheap antenna analyser
Simon,
I understand there are lots of cheaper copies of NanoVNAs which are not genuine and inferior mechanically and technically. Perhaps others here can advise the best sources, but you have to be very careful on EBay.
Better to pay a little more if you are going for one of these.
John
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Re: Null Depth versus Torsion
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
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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
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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
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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?
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James Redding WA9VEZ
Clint Chron