user23991: I'm working on a quadcopter project. The quadcopter will be quite autonomous, but sometimes I'll need to send some messages to it. So I built a simple, one-way RF communication system based on two simple 433 MHz modules.
It works, but when the propellers of the quadcopter approach the take-off speed it begins having trouble in receiving the RF messages, and after a certain speed it stops working.
I suppose this is due to the electrical noise produced by the four little brushed motors. Yesterday I increased a little the transmitter's voltage, and that increased a little the minimum antenna-antenna distance with the motors on, but that is far from enough.
What else could I do to increase the transmitter's power?
Thanks in advance
Noè
P.S.: Here are my RF modules:


user4143: As has been mentioned adding an antenna to the "ANT" pin on the transmitter will help. You need to get the length right though, but it's easy to calculate.
Best is to use single-core insulated wire (0.6mm is a good choice).
To calculate the right length you first need to know your frequency. Then you convert that to the wavelength, and then cut your wire to a quarter of that length.
Wavelength is c/f where c is the speed of light (in m/s), and f is the frequency.
So for 433MHz you have a wavelength of (299792458/433000000) 0.69m.
A quarter of that is 0.173m (17.3cm), so cut your wire to that and solder it on.
For 315MHz the wavelength is (299,792,458/315000000) 0.95m, so an antenna length of 0.238m or 23.8cm.
This is known (unsurprisingly) as a quarter wavelength antenna and is the most efficient length for a simple wire antenna.
Whether it will be strong enough to penetrate the noise from the motors is anyone's guess.
You can also add small capacitors (0.1µF ceramic) across the terminals of the motor and between the terminals and the body, to absorb some of the EMI which may help to allow more signal through - as shown here.

23991: <p>I'm working on a quadcopter project. The quadcopter will be quite autonomous, but sometimes I'll need to send some messages to it. So I built a simple, one-way RF communication system based on two simple 433 MHz modules.</p>

<p>It works, but when the propellers of the quadcopter approach the take-off speed it begins having trouble in receiving the RF messages, and after a certain speed it stops working.</p>

<p>I suppose this is due to the electrical noise produced by the four little brushed motors. Yesterday I increased a little the transmitter's voltage, and that increased a little the minimum antenna-antenna distance with the motors on, but that is far from enough.</p>

<p>What else could I do to increase the transmitter's power?</p>

<p>Thanks in advance</p>

<p>Noè</p>

<p>P.S.: Here are my RF modules:</p>

<p><a href="https://i.stack.imgur.com/LGFOC.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/LGFOC.jpg" alt="enter image description here"></a></p>
 4143: <p>As has been mentioned adding an antenna to the "ANT" pin on the transmitter will help. You need to get the length right though, but it's easy to calculate.</p>

<p>Best is to use single-core insulated wire (0.6mm is a good choice).</p>

<p>To calculate the right length you first need to know your frequency. Then you convert that to the wavelength, and then cut your wire to a quarter of that length.</p>

<p>Wavelength is <code>c/f</code> where <code>c</code> is the speed of light (in m/s), and <code>f</code> is the frequency.</p>

<p>So for 433MHz you have a wavelength of (299792458/433000000) 0.69m.</p>

<p>A quarter of that is 0.173m (17.3cm), so cut your wire to that and solder it on.</p>

<p>For 315MHz the wavelength is (299,792,458/315000000) 0.95m, so an antenna length of 0.238m or 23.8cm.</p>

<p>This is known (unsurprisingly) as a <em>quarter wavelength antenna</em> and is the most efficient length for a simple wire antenna.</p>

<p>Whether it will be strong enough to penetrate the noise from the motors is anyone's guess.</p>

<p>You can also add small capacitors (0.1µF ceramic) across the terminals of the motor and between the terminals and the body, to absorb some of the EMI which may help to allow more signal through - <a href="https://electronics.stackexchange.com/questions/19517/why-connect-capacitors-to-motor-body">as shown here</a>.</p>
