Antenna 101
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@petewill
I'm glad you resurfaced that lost discussion.Did you take a look at the references posted by @a-lurker about magical antenna shapes? A device similar to the zig-zag nRF was well measured in different planes and polarization and it'a all over the board - peaks and nulls in all sorts of directions.
But the zigzag isn't a random thing, it's carefully computed for a given wavelength and impedance. When you are bending and splitting and changing trace widths, the linear length for best matching is no longer as simple to compute as with a simple wire antenna. It's not that they forgot to add the last 3.28 inches, it's that their computations told them they had already reached a good compromise for coverage and making it longer would make it worse.
It's still surprising that soldering a loose wire to some location along the zig-zag so substantially improved your antenna performance. I still suspect some luck was involved, and I would not suggest it unless other solutions didn't work or were not available (eg: changing the antenna orientation). But if it works sometimes (not rarely), then it's useful on the practical level (and a fun puzzle on the theoretic level).
And I'd love to hear the take that better antenna experts than I have on your experience.
I am reminded of my youth, when people would hang aluminum foil fragments on the coat hanger substituting for the broken half of rabbit ears for the TV, and then try all sorts of positions for both ears, seeking better reception. :-) To the degree that this worked (vs just giving a perception of doing something) it was based on doing all that random adjustment while watching the picture and stopping in the best configuration.
@Zeph a zigzag with 10dB and mesured 2 km range: Long range RF link using NRF24L01+ RF Transceiver
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Hello guys!
I am no expert at antennas but I realize some of you have really bad reception.
I got ~450 meters between my nrf24l01+ap and a regular nrf24l01, and this through the house (concrete + wood) and through a forest.
There are some things to take in count;
Antenna orientation, if your gateway (with external antenna) is pointing straight up you have a vertical polarization of your transmission, this basically means that your nodes will work best if they also are vertical.
The radiation-pattern from the external antenna looks like this: http://commons.wikimedia.org/wiki/File:Short_dipole_radiation_pattern.gif
This means in a ideal location with no walls and you were floating in space you basically don't have any reception at all straight above or below the gateway. but since radio waves also reflect from objects you just have very poor reception in the real world.
And looking at the radiation-pattern you'll see that you have the best reception in the blue circles. (and the antennas on your internet router should be pointing straight up if you dont have a multi floor building.)
And because the radio waves reflect, the distance to cables, metal and ground-plane on a pcb matters a lot, if you have wrong distance, you can cancel out the signal almost completely, and you could actually amplify the signal in one direction by having the correct distance. (1/2 wave length = ~61mm if I'm not totally lost today) This is how parabolics works.
Well this is just a very short beginners knowledge and please, correct me and fill in missing facts. I just wanted to get the topic started.. :)
//Damme
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Hello guys!
I am no expert at antennas but I realize some of you have really bad reception.
I got ~450 meters between my nrf24l01+ap and a regular nrf24l01, and this through the house (concrete + wood) and through a forest.
There are some things to take in count;
Antenna orientation, if your gateway (with external antenna) is pointing straight up you have a vertical polarization of your transmission, this basically means that your nodes will work best if they also are vertical.
The radiation-pattern from the external antenna looks like this: http://commons.wikimedia.org/wiki/File:Short_dipole_radiation_pattern.gif
This means in a ideal location with no walls and you were floating in space you basically don't have any reception at all straight above or below the gateway. but since radio waves also reflect from objects you just have very poor reception in the real world.
And looking at the radiation-pattern you'll see that you have the best reception in the blue circles. (and the antennas on your internet router should be pointing straight up if you dont have a multi floor building.)
And because the radio waves reflect, the distance to cables, metal and ground-plane on a pcb matters a lot, if you have wrong distance, you can cancel out the signal almost completely, and you could actually amplify the signal in one direction by having the correct distance. (1/2 wave length = ~61mm if I'm not totally lost today) This is how parabolics works.
Well this is just a very short beginners knowledge and please, correct me and fill in missing facts. I just wanted to get the topic started.. :)
//Damme
I did some testing and analyzing of my microwave RF band.. (hehe)
Channel 76 which is 2476Mhz. and is between wlan channel 13 and 14.
My microwave oven destroys channel 7 - 13 almost completely (2462 - 2472) and affects 6 and 14 too. so a total of 2437 - 2484 mhz is mangled up (Surprises me a bit. And this is no cheap brand, its a quality micro wave, and the cheap one I have in the trash is even worse..)Me myself uses wlan 802.11n (40mhz channels) on ch1. so freq 2400 - 2442 is full also., so the best choice is actually using nrf24 channel above ch 85 in my case (and probobly others too). Could be good to know in future choice of default channel.
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I did some testing and analyzing of my microwave RF band.. (hehe)
Channel 76 which is 2476Mhz. and is between wlan channel 13 and 14.
My microwave oven destroys channel 7 - 13 almost completely (2462 - 2472) and affects 6 and 14 too. so a total of 2437 - 2484 mhz is mangled up (Surprises me a bit. And this is no cheap brand, its a quality micro wave, and the cheap one I have in the trash is even worse..)Me myself uses wlan 802.11n (40mhz channels) on ch1. so freq 2400 - 2442 is full also., so the best choice is actually using nrf24 channel above ch 85 in my case (and probobly others too). Could be good to know in future choice of default channel.
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@Damme Just wondering, how did you analyze your 2.4 GHz band?
Here I read the typical levels of radiation leakage from microwave ovens is about 0.2 mW/cm², which is roughly equivalent to a point source of 6 dBm.
Is your microwave oven maybe leaking? According to this site you can test it placing your laptop in the microwave oven, close the door ... (do not turn the microwave on) and see if you can still ping it ;-)
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@Damme Just wondering, how did you analyze your 2.4 GHz band?
Here I read the typical levels of radiation leakage from microwave ovens is about 0.2 mW/cm², which is roughly equivalent to a point source of 6 dBm.
Is your microwave oven maybe leaking? According to this site you can test it placing your laptop in the microwave oven, close the door ... (do not turn the microwave on) and see if you can still ping it ;-)
@daulagari I had the chance of borrowing a hand held RF spectrum analyzer for a very short while (2h) I would love to do some more scientific measurements on all my transmitting apparatus.. :)
