07/10/2010

Selectivity vs. sensibility.
We saw that we need more amplification to achieve the 0.3 V. So we have to insert an amplificator HF, but there is a problem, beacause of this amplifier the bandwidth of our antenna-tuner-band pass filter widens, and the amplitude of the peak decreased.
There is two important parameter that we have to consider, the sensibility of our system and the selectivity, there first is connected with the capability of detect poor power signal and the second is directly linked with the ability of the filter of cutting out the other station near the station that we want to hear. Is easier to hear that a radio system detect more than one station at the same time that see that the radio hasn' t a fine sensibility.
So we want first of all to preserve the bandwith of our filter, the most simple way to reduce the effect of the resistence of the amplificator HF is to implement a transformer so we can see an higher resistence. (Note that we lose in sensibility.)

Next we have to make this trasformer real in our circuit. To do it we roll (10 times) another wire above our primary coil, and we want to obtain in theory a parameter for the transormar equal to n=60/10=6. So we went to the laboratory and after made it we make some measure and we find that n=6.06. The resistence of the amplificator in HF will be seen multiplied by n.