This article is about a four channel antenna remote control kit that I ordered from Oatley Electronics (https://oatleyelectronics.com):

You can see the circuit working in this video:

The light that you can see clearly is the receiving light (light that turns ON no matter which of the four channels are activated) on the actual receiver circuit (the only part of the kit that I did not need to solder). You can notice the other four LEDs above the receiver light and do not appear as clearly as the receiver light in the video.

Step 1: Arrange the Components

This is the transmitter device:

The small LED turns ON when any of the four buttons are pressed. The frequency of the transmitter is not written on the back of the transmitter device. You will need this frequency if you are calculating the length of the wire for the dipole antenna wire.

This is the receiver circuit:

The big silver component is the crystal, possible used to generate a precise frequency for an oscillator. This frequency could be either used to demodulate the received radio signal or for the microcontroller timer. You can see the surface mount components (SMC) on this circuit. You can see the white button on right side of the circuit. You need to press the white button to active the circuit.

D0, D1, D2 and D3 are the four channel outputs:

The Vt pin turns ON when any of the channels receives the signal (the bright light that you see in the first video). You can see the antenna label on the top right corner.

You can purchase those receiver circuits on eBay for a very small cost. 

The kit circuit also consists of the ULN2003 relay driver.

Step 2: Make the Circuit

The blue wire is connected to Vt output via the ULN2003 relay driver.

You can see the small black disk/cylinder on your left. This is the diode rectifier IC (integrated Circuit) that used for electrical isolation of 9 V and 12 V power supply inputs. That means both 9 V and 12 V power supply inputs can be connected simultaneously.

The other four channels are SPST (Single Pole Single Throw) relay activated channels.

The length of the blue wire antenna depends on the wavelength and wavelength is dependent on the frequency. Wavelength is equal to:

Wavelength = Speed of Electromagnetic Wave / Frequency

(Click on this link for more information: https://en.wikipedia.org/wiki/Wavelength)

Thus the higher is the frequency, the lower is the wavelength and thus the shorter is the required length of the wire. You can assume that the transmitter wave is traveling in vacuum at the speed of light (3 × 10^8 m/s). This video will show you why the length of the wire should be half wavelength long for two wire/two pole dipole antennas and one wavelength long for single pole dipole antennas (because you are using one wire not two for this kit):

Second video:

The wire antenna is included in the kit. Thus you do not need to do any calculations. I noticed you do not need a precise length of antenna wire for a reasonable receiving range.

Step 3: Testing

Testing included settling time test:

Testing also included four channel relay control test:

Vt current output:

Step 4: Applications

This me using the remote control as a drum:

Remote controlled lamp:

Conclusion

This remote control kit is useful for implementing keyless entry in old cars, remote controlled lamps, toys, remote controlled cars or remote controlled boats.