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I am trying to communicate between two arduino microcontrollers using radio. For this purpose I am building a whip antenna with 4 ¼ wave radials. I've done a bit of reading and have got most of it, but all guides I've found are a bit vague on the topic of radials.

So my question is: When it says that Radials should be grounded, does that mean they have to be connected to the actual ground, or is the ground Pin on the arduino (the "minus pole") ok too? As my project is mobile, actual ground is pretty tough...

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    $\begingroup$ What is ground and what does it do? $\endgroup$ – Phil Frost - W8II Apr 12 '17 at 14:46
  • $\begingroup$ For the Arduino, you can use the HC-12 and a full power supply on the Arduino to handle their power requirements. It is easy to program them and they get surprisingly great distance in the 300 MHz range. Note I said full power supply. When you first try them and all you have is the USB power, they won't work at all. You really do need a Vin that can handle the HC-12s. Another good alternative is to connect the Arduinos via serial to Raspberry Pis with the Arduino IDE. Then you can remotely program them and communicate with them via WiFi. $\endgroup$ – SDsolar Apr 12 '17 at 19:35
  • $\begingroup$ friendly reminder: please accept an answer or clarify what is not satisfactory about the answers you've gotten. This site stops working if askers don't give feedback!! $\endgroup$ – Marcus Müller Apr 15 '17 at 10:21
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The radials are not connected to the earth. Here's a photo of a ground plane antenna. They are connected together as shown to the coax shield. This shield should be connected to the common on the board that can serve as an RF ground.

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  • $\begingroup$ So with other words, yes, I can just connect it to the GND pin on the micro controller? (which, in case you are not familiar with arduino, is "minus") $\endgroup$ – user5227744 Apr 12 '17 at 12:22
  • $\begingroup$ @user5227744 Connect it to the ground pin, yes. $\endgroup$ – Mike Waters Apr 12 '17 at 13:25
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Radials are grounded to the feedpoint.

For instance, the shield of the coax feeding the quarter-wave antenna. For AM radio broadcasting stations, there are radials every 3 degrees (120 of them) and they are generally buried (enough so you can still mow the lawn above them), so they are at ground potential their entire length.

If the radials are not themselves grounded then that is called a counterpoise, like if you install a radial system on a rooftop. In that case the true ground is at your transmitter, then the feedline shield is the connection to the counterpoise on the roof.

In terms of Amateur Radio usage, there are a lot of great antennas like the Hustler 5BTV that require professional-quality ground systems.

Another example is if you use a magnetic mount for your antenna on the car, it couples into the metal of your car as the ground plane.

I think the best answer to your question can be found HERE - the basic concept is shown in this diagram:

2M Ground Plane Antenna

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The radials scope are to emulate a "ground plane" in order that your antenna to have maximal radiated lobes according this design. Also will contribute to proper impedance matching your cable (and/or transmitter).

When 100% matched, all energy transmitted will be transferred to active element and radiated, other ways, some percent will be reflected back through cable.

From RADIATING point of view, there is no need to connect them to anything, coupling will be magnetic. For GP antenna (and most vertical ones) you can skip radials and put a solid ground plane like GND cooper of PCB. Imagine that car antennas don't use radials, just substitute them with car roof.

From IMPEDANCE MATCHING point of view, you will need somehow to match 50R cable to your vertical wire and for example car antennas will use a small inductor on the base to do that. GP antennas often use a stub or just live with a small mismatch, but use that "virtual ground" (the radials) to match.

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