Audio Power is written in C# and uses NAudio , Zedgraph and Lomont’s FFT .
Click on screen shots below to get a larger picture
It basically calculates the average power of a number of audio samples. It can also display raw ADC input , FFT etc
SUN NOISE MEASUREMENT
I wanted to have an accurate way of measuring the well known “Sun Noise” of my 23cm Moonbounce setup. The narrowband (a few kHz) baseband output of the SSB receiver is connected to the sound card.
Comparing the received power (S) when pointing the antenna at the Sun or any another signal source with the noise (N) when pointing it at the quietest point in the sky gives a good estimation of reception capabilities.
Maximizing this Signal to Noise ratio (SNR) by modifying the antenna , LNA etc ensures best reception.
Higher signal S means that the antenna has higher gain.
But just increasing the gain of an antenna does not mean that reception will get better because noise received is also as important.
Less Cold sky power means that the antenna receives less noise.
Just decreasing noise without looking at antenna gain is also not enough.
The sound card can be used for simple audio power measurements. Obviously , there is a larger number of apps available like the excellent SpectraVue etc which can be used to measure audio power.
But writing its own software is part of the fun . There were many new things to learn . I had to figure out how to access audio samples in C# , how to display data and calculate FFT efficiently.
To access sound samples NAudio library was used .
Zedgraph makes plotting really easy and it is very fast as well.
For FFT display, I found Lomont’s implementation fast and efficient.
USING AUDIO POWER SOFTWARE
After selecting Capture device, sample rate , number of samples used for averaging and time span to be shown , click “CONFIG” button. Hitting “START” button will enable sound capturing and the results will be displayed in the plot below.
Adjust sound card input sensitivity within Windows Mixer .
There is a button “Open Windows Mixer(WinXP)” that will open the necessary controls. At the moment, this only works in Windows XP.
To stop capturing and possibly modify settings hit “STOP” change parameters , hit “CONFIG” and then “START” again.
Hitting button “STORE A” or “STORE B” stores the current averaged power to the text box next to the button.
Hitting “DELTA” will calculate the difference and show it in the text box.
For example, point at the sun and hit “STORE A”. Point at cold sky and hit “STORE B” . Hitting “DELTA” will give you the difference or the SUN NOISE / COLD SKY ratio in dB.
Besides average power, the software can also display raw sound card samples , a simple FFT vs time, DC and average value of incoming samples, Delta between averaged samples, FFT peak power and frequency.
Please send me your comments and bug reports !
Michael Margaras , SV1CAL