LoRa - Long-Range Radio for IoT | Arduino, ESP32, RPI Pico

@inq I am not sure if this helps but. CB freq is about 27 MHz and it was not uncommon to see 5ft whips on cars. Sorry, I am in a hotel getting ready to leave so no time to do the math. I will add though that many CB antennas had a large 'gizzmo' at the base to 'enhance the signal'. I am also remembering from my amateur radio days something about a SWL meter, and an antenna tuner where the coax entered the house. BTW, the Swiss guy is very big on LORA, he may have some info.

Posted by: @davee

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The 50 Ohm characteristic is an AC impedance characteristic.

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The worst case (possibly) being when waves constructively add to extent that the voltage experienced can exceed the voltage rating ... and shorts, magic smoke, etc. appear soon after.

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A commercial co-ax cable specification should include the dB loss per unit length (say per 100 metres), so you can estimate what fraction of the signal will emerge at the far end.

Posted by: @davee

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Which brings up why do some antenna's come in pairs and they are 90° to each other instead of 180°?

Sorry, I am not clear what you are referring to. Maybe you are thinking of something like the 'home' WiFi routers that come with two or more rotatable quarter-wave aerials.

I'll just clarify, but not really wanting to open another present.  It is very difficult to get cell or Internet service in my area.  Until Starlink, it wasn't really possible at my house... at all.  I couldn't even get 57K modem, much less DSL over telephone lines.  The best was cell-phone Internet $$$ and metered.  While out an about, my cell phone could often get in the teens Mb/s.  Just one mile off the main road, I was lucky to get anything and it rarely exceeded 1Mb/s.  I even tried antennas like this that have two at 90 degrees, but neither even covers the plane of the ground.  Seems like another aspect going on here.

Posted by: @davee

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Wikipedia has several articles with useful information, including:

https://en.wikipedia.org/wiki/Antenna_(radio)#Effect_of_ground

and https://en.wikipedia.org/wiki/Monopole_antenna

This whole subject is amazing in its complexity.  Even the ground shape and distance from the ground, orientation to the ground, grounding, dielectric material, coax geometry, wire lengths (except strangely coax length seems to play nearly no tuning role).  It seems miraculous that radio ever came into being.  Everything is dependent on everything else.

Posted by: @davee

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if you are having trouble sleeping:

Who can sleep with nightmares like these?

Posted by: @davee

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Plus if we look at conducting frequencies in the GHz and above range, waveguides are commonly selected, which (somewhat facetiously), are more reminiscent of water plumbing than electronic wiring. e.g.

https://en.wikipedia.org/wiki/Waveguide_(radio_frequency)

🤣 Yes, it looks like something out of Steampunk!

Posted by: @davee

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Sorry, I wouldn't know where to start in predicting all the possible gotchas.

That does not mean, you are doomed to failure

Oh yeah it does!  If I merely focus on one thing and think, "I can tweak this little aspect", but in reality it un-does half a dozen other. 

Posted by: @davee

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It is too late tonight for me to go through the equivalent calculation for capacitance, but hopefully you can see the principle. Note in this case, XC goes down, as the frequency increases. Let me know if you have any queries.

I have soldiered you through a terrible war.  I think we can cordon these pages off and bookmark it for the next fool that thinks their going to make a better antenna and asks the question, "What if..."  

It's hard to look at a mere piece of wire 8.19 cm long and not think it can be improved upon.  Yet the Physics and Mathematics behind what I spent all of 10 seconds to cut and solder on the PCB is just staggering!

I'm sold... I'll use the wire and be happy in now knowing it's the best that it's going to ever be.  😫 At least I now understand why it's so complex and that when someone says step away, I might just trust they are just protecting me 🤣 from my own folly.

Thank you again Dave.

@inq , Your quite welcome Dennis...Yes, as you can see, while the principal theory is complex, the actual implementation of aerials (antennas) are straight forward.

In the days when CB was the "thing" , it was not uncommon to see large whips on cars and truck with "loading coils" on the base of the antennas so as to "tune" the whip to the correct wave length. Spent many hours tuning aerials with special equipment, ie: SWR meters, to optimize the power output to get the max distance out of the transmissions..lol

Occasionally we employed the ionosphere to "skip" the wave much longer distances.. this only happened when the weather conditions were just right to "bounce" the signal off the ionosphere. This resulted in receiving/transmitting a signal hundreds of miles! I once talked to a fellow CB'er that was in Chicago, Ill. while I was in Pensacola, Fla....790 miles (flight).

Glad to see that it's helped you to understand the basic fundamentals.. also, @davee explanation of XL/XC and it's relationship to frequency, impedance, and dc resistance should now provide you with the complexity of how circuit design parameters are important, and why circuits are a hit and miss to hobbyist sometime...lol

At any rate, I love to see people trying to understand, and as for me, much of this stuff I haven't even thought about for over 50 years now since I studied it in tech school( 1966 and again in 1973), good refresher course for me as well...hehehe!

regards,

LouisR

Yes Louis, that one little aspect has bothered me for decades.  I have always thought, "don't I need to connect this to something?"  I remember looking at TV antenna and realizing that the only thing hooked to the wire is only 1% of the antenna.  The other 99% is not physically connected by anything that can transmit electricity.  I know the word "lensing" comes into it, but I don't want to ask.  Put a fork in me, I well done.

Posted by: @inst-tech

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Spent many hours tuning aerials with special equipment, ie: SWR meters, to optimize the power output to get the max distance out of the transmissions..lol

I remember CB's.  Dad had one, but I never got the itch. 

From this kind of "tuning" concepts, do you see any hobbyist level affordability to do the same thing with the higher frequencies.  I think I'm understanding @davee's teachings to say the concept is the same, but because the frequencies so high the equipment to distinguish at a fine enough resolution to be useful is unaffordable except for dedicated labs and the "trimming" is down in the micro-meters.

@inq Correct.. no there is no reasonable ability to "tune" at the higher frequencies because of the things you already mentioned..The science of antenna theory and application has already taken that into consideration and now we have the benefit of being able to buy (purchase) said antennas at a reasonable price from a myriad of places.

I think you'll be happy to know that you don't have to do that, and just apply what you know into your projects with the knowledge of when things go side ways, you'll at least know why!...lol 

Keep up the good work my friend.. sally forth!

Regards,

LouisR

@inq , After I had posted my last response, I did a little research and found this link:

It's a how to make a 915MHz LORA antenna, various types,and inexpensive! 

I know that should appeal to your wallet...hehehe

Happy antenna making!

regards,

LouisR

Hi @inq,

• Re: your followup about: Which brings up why do some antenna's come in pairs and they are 90° to each other instead of 180°?

I don't know really know what those two 'blade' shaped boxes at 90 degrees to other are doing, but maybe it is worth considering life as an antenna ... and apologies if all this is obvious...

1. If you have a spherical light bulb (old skool type) with a tiny screw fitting, then, very roughly, the light goes equally in all directions.
2. If you add reflectors and maybe lenses, you can direct most of the light in a particular direction, then you will get much more light in that preferred direction, but not much everywhere else.
3. If you included a polariser in the path of your lenses, your light would be polarised.
4. Now take a pair of polarised sunglasses, and make them so the polarisers are rotatable, with a link that means that they are always 90 degrees different in rotation angle.
5. On a dark night, with no moon or artificial lighting, look at the light from your modified torch (at a suitable safe distance), and rotate the sunglass's polarisers to get the maximum light through the right eyepiece ... then look through the left eyepiece ... it should be 'dark', as the polariser on the torch is 'crossed' (at 90 degrees) with respect to the left eyepiece.
6. Now if you look at places away from where the torch is shining, you can see very little.
7. And where the torch is shining, in general,  you can only see things through right eyepiece, although a few things are visible, because they are changing the polarisation angle of the light on reflection.

So you now have life as an aerial based on a monopole (quarter wave) or dipole (half wave aerial)!

The simple monopole or dipole is omni-directional with respect the axis through the 'wire' of the aerial, but the waves are polarised. Two monoples or dipoles within reasonable range and direct sight of each other, with one vertical and the other horizontal, will pick up very little signal from the other, as they are in a similar predicament to that of the two crossed polarisers.

Similarly, two monopoles or (half-wave) dipoles on the same colinear axis will pick up every little signal, because the majority of the signal is sent perpendicular to the 'wire' axis of the aerial.

And if a transmitter aerial focuses most of its signal in one direction, by having additional parts consisting of directors, and reflector, whilch could be a parabolic dish, then if that direction is away from the receiving aerial, obviously, it is not going to receive much signal.

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So my guess is that your 'bladed' aerial is trying to play the statistics game of betting on more than possibility. e.g. Perhaps it is aiming to send some signal on one polarisation and some at 90 degrees to that polarisation, so there is no 'null' angle with zero signal.

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Of course, polarising sunglasses are filters, relying on your eyes to detect the light, whilst the aerials have an inate 'polarisation filtering' effect, as well as picking up the signal, so to some extent this is an analogy, rather than direct equivalence, but hopefully it is useful.

Best wishes, Dave