Solo GNU Radio Companion Assignment – Pirate AM/FM radio station Project
In this project I am going to create radio station that will connect two computers through two kind of modulation AM and FM.
AM modulation:
Amplitude Modulated (AM) radio signals transport an audio signal (electrical material that can be transformed to sound). The audio information is encoded on the radio wave by changing the amplitude of a high frequency radio wave. The base frequency of the radio wave (called the carrier wave) is much higher than the frequency of the audio information it carries (915MHz).
The AM transmitter components are as they are in figure1-1:
· Wave file source to upload the wav file to the GnuRadio companion which get multiply by a constant to increase the amplitude and I add a Throttle to reduce the CPU usage.
· This will take us to the Low Pass Filter that will take off all the noise frequencies over 5K.
· The Signal Source gets multiplied by the message signal to create the modulated signal.
· The Rational Resampler this block is used to convert from one sample rate to another which I left the decimation 1 and the interpolator 1.
· I have Osmocom Sink that will transmit at the 915MHz frequency.
· Variables:
· Sample rate of 2MHz.
· RFgain Slider from 100 to 300 to change the RF gain on the transmitted signal.
· BBgain Slider from 0 to 300 to change the BB gain on the transmitted signal.
· Freq Slider to adjust the frequency from 915MHz and 2.14GHz
· WX GUI FFT Sink to show FFT scope as we can see in Figure1-2.
Figure 1 -1 AM Transmitter Block
Figure 1-2 AM Transmitter sink
The AM receiver components are (figure1-3):
· RTL-SDR Source will receive the transmitted signal from the other laptop by the antenna in 914.94 frequency.
· Low Pass filter will cut off all the frequencies that higher from 5k to keep the transmitted only without the carrier.
· AGC2 to control the gain with Attack Rate of 625u and Decay rate on 10u.
· We convert the complex data to magnitude in float by using Complex to Mag.
· Multiply by Const to reduce the amplitude by 50m rate.
· Rational Resampler is used in this block to prepare the signal to the Audio Sink by 441 interpolation and 2K decimation.
· Audio sink to communicate with the laptop audio card.
· WX GUI FFT Sink to tune the radio on the make sure that we are in the right carrier frequency.
Figure 1- 3 AM Receiver Block
Figure 1-4 AM Receiver Sink FFT Plot
FM Modulation:
To generate a frequency modulated signal, the frequency of the radio carrier is changed in line with the amplitude of the incoming audio signal. When the audio signal is modulated onto the radio frequency carrier, the new radio frequency signal moves up and down in frequency. The amount by which the signal moves up and down is important. It is known as the deviation and is normally quoted as the number of kilohertz deviation.
the signal has to be demodulated at the receiver that will be enable the frequency variations of the incoming signal to...
