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Automatic Antenna Tuner for QRP controlled by Android and Arduino - Part 2

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Published on Dec 10, 2012

First of all my apologies for the mistakes in English.

Documentation about this project on https://github.com/pu2clr

I would like to show you a Magnetic Loop Antenna working with an Antenna Tuner controlled by Android and Arduino. The system presented here is a compact version of the systems featured in the video "Automatic Antenna Tuner for QRP with Android and Arduino - Part 1".
Some times working with a Magnetic Loop Antenna can become uncomfortable because you have to tune the antenna every band or even frequency that you want to use. If you use a Magnetic Loop Antenna you have noticed that it works as a band pass filter. This feature is very nice, specially for listening station.
However, if you want to change the frequency of the radio you have to go to the Antenna and tune it to the new frequency. If you want to know more about Magnetic Loop Antenna, see http://www.alexloop.com/.

In my antenna, I introduced a system that gives me the possibility to tune it remotely. That means I can change the frequency of my radio and tune my antenna without leaving my seat.
Up to now, there is no new about this subject. You can see many kind of remote controls to magnetic loop antenna on the Internet. In my project, I chose to control my antenna from a Mobile Phone with Android System. In addition, I introduced to the system, an SWR meter that enable an automatic tune. During the course of the capacitor of the antenna tuner, the Arduino saves the capacitor position and records the value of the SWR.
Once known the position of the capacitor which results in lowest SWR, the tuning is performed.
For listening, you can use three kind of controls: Extra Fine, Fine e Fast tuning.




Question about noise during reception:

Before I starting this project, I was worried if the Arduino could cause unwanted noise or interference in my reception during data processing.

Actually, there is a crystal that oscillates at 16MHz on Arduino board.
But I have not noticed its or any other source of interference in the system.
I mean, after tuning the antenna, even turning off the system, I do not notice any difference about noise.
In part, this may occur because the high selectivity of the magnetic loop antenna. The bandwidth is very narrow in this kind of antenna.

Anyway, on a final version of a project like this, I think it is better idea to use a metal box to shield the microcontroller circuit.



Next steps:

1) Tuning a magloop for maximum receive noise.
To do that I can plug the output sound jack of the radio to the input mic of Android device. Of course, I have to adjust the input and output impedance.
Well, in this case, I can use an algorithm very similar to the minimum SWR Scan that I have used in my last project with Android and Arduino. But now, I have to scan (processing) for the maximum noise.

2) Adding a motor to rotate the antenna (direction of the antenna).



Documentation and source code:

Download Photos, Schematic and docs - https://github.com/pu2clr/AntennaTune...
Download the Android source (Eclipse Project) - https://github.com/pu2clr/AntennaTune...
Download the Arduino source - https://github.com/pu2clr/AntennaTune...

See also.
Automatic Antenna Tuner controlled by Android and Arduino - Part 1 - http://youtu.be/55bQ9xVWzuM
Antenna Tuner controlled by Arduino and Android via bluetooth - http://youtu.be/WZdym3Iu8-8
Antenna Tuner controlled by Arduino and Android Teste I - http://youtu.be/PGNcaqG6wXk
Magnetic Loop Antenna controlled by Arduino - http://youtu.be/b3hUpQvO38k

73.
PU2CLR.
Ricardo.

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