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This is part 45 of the LoRa/LoRaWAN tutorial.
In this tutorial I will explain what a normal mode helical antenna is.
In literature the coil antennas are called helical antennas and are invented by John D. Kraus.
Helical antennas can be made to operate in one of two ways: normal mode or axial mode.
Spreadsheet:
www.mobilefish.com/download/l...
In axial mode, the antenna is circular polarised and radiates in the direction of the helix.
These antennas are directional.
The diameter (D) and pitch (S) of these helical antennas are roughly comparable to the wavelength.
Axial mode helical antenna card deck:
www.mobilefish.com/download/l...
In normal mode, the antenna behaves like a monopole antenna (see tutorial 42) but are smaller in size and produces an omnidirectional radiation pattern, and is linear polarised.
The diameter (D) and pitch (S) of these helical antennas are small in comparison to the wavelength.
As mentioned earlier I created a UKposts video: "How to create a copper 868MHz coil antenna"
• How to create a copper...
The normal mode helical antenna demonstrated in the UKposts video is based on:
www.professor.com.tw/upLoad/pr...
Based on the above mentioned design I have created an antenna model in the 4NEC2 program.
4NEC2 card deck:
www.mobilefish.com/download/l...
I could not verify if this normal mode helical antenna is a valid design.
I decided to create my own self designed normal mode helical antenna.
The 4NEC2 card deck:
www.mobilefish.com/download/l...
My self build normal mode helical antenna performance is compared with a sleeve dipole antenna.
For this test I am using the end node and antenna C as demonstrated in tutorial 33.
More information about this end node, see:
www.mobilefish.com/developer/...
The end node uses the MCCI LoRaWAN LMIC Library:
github.com/mcci-catena/arduin...
The end node uses the following sketch:
www.mobilefish.com/download/l...
The logged data can be found at:
www.mobilefish.com/download/l...
One or more gateways were able to receive my transmitted sensor data, see:
drive.google.com/open?id=18SK...
If you look at the results you may notice there is no significant difference in the average RSSI values between the normal mode helical antenna with ground plane and the sleeve dipole antenna.
If you look at the time it took to transmit 15 messages there is almost no difference.
When using the normal mode helical antenna with ground plane it took 8.5 minutes to transmit 15 messages.
When using the sleeve dipole antenna, which is my reference antenna, it also took 8.5 minutes to transmit 15 messages.
But when using the normal mode helical antenna without ground plane it took 14.5 minutes to transmit 15 messages.
Looking at the results I can conclude that my self build normal mode helical antenna with ground plane performs the same as the sleeve dipole antenna.
The normal mode helical antenna without a ground plane does not have a good antenna performance.
A normal mode helical antenna is impossible to build accurately by hand.
If you have to choose between a normal mode helical antenna or just a monopole antenna, I would choose a monopole antenna, because a monopole is easier to make.
But if a monopole does not fit inside a container, than try a normal mode helical antenna.
These antennas are smaller in length.
If your project allows you to use a sleeve dipole antenna (see tutorial 43) I would prefer using a sleeve dipole antenna above a monopole or normal mode helical antenna.
A normal mode helical antenna behaves like ¼λ monopole antenna.
Without a good ground plane the antenna will not perform well as explained in tutorial 42.
If you use a ¼λ monopole antenna or normal mode helical antenna without a good ground plane the signal can be transmitted over a distance of 100 m or even more.
But if the distance is increased the signal will be weaker with increase data package loss.
This is based on my experiments and situation.
Check out all my other LoRa/LoRaWAN tutorial videos:
• LoRa/LoRaWAN tutorials
Subscribe to my UKposts channel:
/ @mobilefish
The presentation used in this video tutorial can be found at:
www.mobilefish.com/developer/...
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