Let's do it.
We said that we have to built a pass band filter that also act as a tuner. If it's possible we want also that the filter is able to amplificate our signal so we can respect the condition on the volt that have to be more than 0.3 so that the envolope detector can works.
José Maria has shown us a very clever solution based on the series of a resistor an inductor and a capacitor. Formally this is a low pass filter but if we choose parameters properly that filter show a peak in the frequency that we want... and so we have the pass band filter and also the amplificator!
I was very impressed when we saw that a simple antenna (coil and ferrite) in parallel with a capacitor (variable) act perfectly as the scheme that we saw for the passband filter, so in the end we have our antenna that is the same of having an antenna, a passband filter, a tuner and an amplificator. Incredible.
In the second part of the lecture we study how we have to make the coil since we have our variable capacitor (we have to buy it). We found that we have to make 60 rotations around the ferrite.
After that we went to the laboratory and we start to make it, in the first time seemed simple but if you want to make it well you have to do a little effort. Now i' m curios to measure the performance of it.
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