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Author Topic: RF 10.7MHz emission lobe measurement  (Read 1396 times)
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[email protected]
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« on: March 17, 2020, 06:09:37 18:09 »

dear all, I need to measure the lobe of an 10.7Mhz tx antenna, directionality and signal, it consists of 9 coils wrapped in air, in front of it I've the rx antenna and near there are also other similar antennas.
I need to know if the antennas influence each other, the maximum reachable distance and directionality.
Thanks
Massimo
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bigtoy
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« Reply #1 on: March 19, 2020, 04:43:56 16:43 »

10.7 MHz has a wavelength of about 28 metres. It's going to be difficult to measure its radiation pattern, even outside in a large field, because of that. You can try, walking around the antenna with a handheld dipole and a battery operated spectrum analyzer, while the antenna is transmitting. The goal is to draw a line around the antenna that has a constant signal strength. Tough to do in the vertical plane however! You can try getting creative. It's probably a great deal easier simply to simulate it - there are EM simulation programs on this site.
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[email protected]
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« Reply #2 on: March 20, 2020, 06:14:36 18:14 »

 Shocked

But my antenna is a coil in air of a diameter of 32mm with 9 spires, tx signal is a sinusoidal 5,5Vpp @10.7Mhz, unfortunatelly this is which the enginer has projected few yaer ago and I don't have way to contact him.
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token0
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« Reply #3 on: March 21, 2020, 03:42:16 03:42 »

You can try to simulate it in MMANA-GAL software http://gal-ana.de/basicmm/en/
It has free version for non-commercial use.
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Caaarlo
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« Reply #4 on: April 07, 2020, 01:09:34 01:09 »

dear all, I need to measure the lobe of an 10.7Mhz tx antenna, directionality and signal, it consists of 9 coils wrapped in air, in front of it I've the rx antenna and near there are also other similar antennas.
I need to know if the antennas influence each other, the maximum reachable distance and directionality.
Thanks
Massimo

Pictures of the setup would help a lot. All small loop antennas have quite similar radiation patterns. It could be omnidirectional if the loop is placed horizontally, or bidirectional if the loop is placed vertically. A dipole has a very similar pattern with 2 theoretical nulls. So there is no front/back directivity.



Regarding gain and signal, it's no easy task. The usual method is far-field and some instruments and antennas are needed. You can find some thechniques at Owen Duffy's blog.
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fpgaguy
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« Reply #5 on: April 07, 2020, 03:10:12 03:10 »

I assume you have a receiver for this right ?
You should be able to get RSSI reading from the receiver

Place antenna with transmitter on a rotating lazy suzan type device, with a string wound around it.    record the RSSI, and slowly pull on the string to rotate the antenna.
For vertical measurement, rotate the antenna 90 degrees along y or x, and repeat

Keep all objects out of path between antennas

Not perfect, but will get you good idea - and also you don't need to move the more complex receiver around




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[email protected]
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« Reply #6 on: April 21, 2020, 10:25:24 22:25 »

I assume you have a receiver for this right ?
You should be able to get RSSI reading from the receiver

Place antenna with transmitter on a rotating lazy suzan type device, with a string wound around it.    record the RSSI, and slowly pull on the string to rotate the antenna.
For vertical measurement, rotate the antenna 90 degrees along y or x, and repeat

Keep all objects out of path between antennas

Not perfect, but will get you good idea - and also you don't need to move the more complex receiver around


receiver is alway an air coil with same diameter of tx antenna, your idea is use an experimental method

Posted on: April 21, 2020, 10:17:57 22:17 - Automerged

Pictures of the setup would help a lot. All small loop antennas have quite similar radiation patterns. It could be omnidirectional if the loop is placed horizontally, or bidirectional if the loop is placed vertically. A dipole has a very similar pattern with 2 theoretical nulls. So there is no front/back directivity.



Regarding gain and signal, it's no easy task. The usual method is far-field and some instruments and antennas are needed. You can find some thechniques at Owen Duffy's blog.


Great! this gives me an idea of ​​the signal, and maybe can suggests how to get the lobe, if I meausure the signal intensity with an antenna until signal goes down I can find toroid radius if i meausre on x or y and also measure on z axis and if I apply math of thoroid i can found the lobe geometry
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rtm
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a.k.a. klug


« Reply #7 on: April 22, 2020, 09:52:52 09:52 »

What you are trying to do is an exercise in futility.

It is near impossible to measure a real diagram of such antenna in home conditions.

Everything around you is a mirror. Even ground is a mirror too. Walls, wires, tubes in house warming system are reflecting your signal. So, you have not only one signal coming from your TX antenna, but a lot of reflected signals coming from different unpredictable directions.

How to measure antenna diagram correctly:
1) It must be an open field without any object around it. In this case, we will avoid reflections.
2) For better results, we need to use a directional antenna in RX point.
3) A distance between TX and RX antennas as a rule must be more than 10 wavelengths.
4) We have to make a number of different experiments on different attitudes (up to few wavelengths) because ground is reflecting too.

You see, it is quite difficult to make, but you can approach some of these conditions. Or better, follow the advice given by token0.
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[email protected]
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« Reply #8 on: April 23, 2020, 12:06:22 00:06 »

What you are trying to do is an exercise in futility.

It is near impossible to measure a real diagram of such antenna in home conditions.

Everything around you is a mirror. Even ground is a mirror too. Walls, wires, tubes in house warming system are reflecting your signal. So, you have not only one signal coming from your TX antenna, but a lot of reflected signals coming from different unpredictable directions.

How to measure antenna diagram correctly:
1) It must be an open field without any object around it. In this case, we will avoid reflections.
2) For better results, we need to use a directional antenna in RX point.
3) A distance between TX and RX antennas as a rule must be more than 10 wavelengths.
4) We have to make a number of different experiments on different attitudes (up to few wavelengths) because ground is reflecting too.

You see, it is quite difficult to make, but you can approach some of these conditions. Or better, follow the advice given by token0.

The project is not mine, it's already done, they asked me to optimize the RF part, the project is an tx antenna and rx antenna between them pass a metallized film, in function of attenuation they know metal thikness.
The projected distance between tx and rx is 4.5 cm.
The problem is the influences of nearby devices the always tx/rx couples. I looking for if changing the position, or form of antennas change directivity e lobe.

I tried to follow the advice given by token0, but it's not clear to me how to  create a coil antenna in the program...

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flyback
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« Reply #9 on: April 23, 2020, 02:49:15 14:49 »

hello [email protected],
from what you described, this is a near field communication, ie with magnetic field rather electric field.

Hereunder some reading suggestions,
https://www.researchgate.net/publication/332382197_Magnetic_Field_Shaping_Technique_for_HF-RFID_and_NFC_Systems\\http://propagation.ece.gatech.edu/ECE3025/opencourse/MSF/MagRFID.pdf
https://www.st.com/resource/en/application_note/cd00221490-how-to-design-a-1356-mhz-customized-antenna-for-st25-nfc--rfid-tags-stmicroelectronics.pdf

All these links are for 13.56MHZ RFID, but the concept should be applicable for your project. The one from ST is interresting.
Good luck.


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