http://imageshack.us/photo/my-images/12/tda7000a.gif/
From the schematic above.. at pin 6 of the TDA7000, that is the local oscillator based on the user's website.
by calculating the values, the
frequency when that PVC is at 2pF = 1/[2*pi*squreroot(LxC) ]
where C = (2pf||56pf) + 33pf
where L = 56nH
= 113Mhz
frequency when that PVC is at 60pF = 1/[2*pi*squreroot(LxC) ]
where C = (60pf||56pf) + 33pf
where L = 56nH
=85Mhz
Pretty much, it covers the 88Mhz to 110Mhz FM Stations
1st question:
is my calculation correct? because when we built the circuit, the station were moved, wherein if we moved the PVC to it's Maximum, the station is at 98Mhz or something (It cannot reach more than 100Mhz stations). What we did is to reduce that 33pf to a lower value (10pF) to adjust the stations (The coil was adjusted few times before we did the replacement of cap). So, what was the culprit then? Does the copper at the pcb's board can add some extra capacitance to the local oscillatorr? since our PVC was located a few mm from the inductor and other cap.
2nd question
if that pin 6 is the local oscillator... what was that coil and two capacitors at pin 13 and 14 are used for? some circuit doesn't have that. what was the pros and cons of not having that in that circuit?
From the schematic above.. at pin 6 of the TDA7000, that is the local oscillator based on the user's website.
by calculating the values, the
frequency when that PVC is at 2pF = 1/[2*pi*squreroot(LxC) ]
where C = (2pf||56pf) + 33pf
where L = 56nH
= 113Mhz
frequency when that PVC is at 60pF = 1/[2*pi*squreroot(LxC) ]
where C = (60pf||56pf) + 33pf
where L = 56nH
=85Mhz
Pretty much, it covers the 88Mhz to 110Mhz FM Stations
1st question:
is my calculation correct? because when we built the circuit, the station were moved, wherein if we moved the PVC to it's Maximum, the station is at 98Mhz or something (It cannot reach more than 100Mhz stations). What we did is to reduce that 33pf to a lower value (10pF) to adjust the stations (The coil was adjusted few times before we did the replacement of cap). So, what was the culprit then? Does the copper at the pcb's board can add some extra capacitance to the local oscillatorr? since our PVC was located a few mm from the inductor and other cap.
2nd question
if that pin 6 is the local oscillator... what was that coil and two capacitors at pin 13 and 14 are used for? some circuit doesn't have that. what was the pros and cons of not having that in that circuit?
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