18-05-2022, 07:49 PM
(This post was last modified: 18-05-2022, 07:52 PM by Mike Watterson.)
Yes, on AM/FM superhet ICs there is just a simple switch added to pad tuning cap and add the coil. To an extent you can change the extra cap larger if the coil is lower inductance and vice-versa.
I've actually got or had a radio with that IC. I had the datasheet already.
For MW Pg 11
1 & 2 is 106 turns
3 & 4 is 7 turns
So for LW about 210 turns = x4 inductance which would be only reduction to 400 kHz ) and also padding capacitor to lower frequency more and reduce tuning ratio. So possibly 250 to 300 turns. secondary would be about 14 to 20 turns.
IC Pin 2 is AM in (from smaller winding via switch. IC pin 4 is AGC so MW & LW secondary coils can be common
One side of tuning cap is to common/OV, the other side should go to coil primary of LW or MW via switch. One end of each primary coil goes to common/OV>
See page 9.
You can put a three way switch and do SW band too. A trimmer in series with tuning capacitor rather than to 0V. Maybe 20 turns to 5 turns on a small ferrite and capacitor to FM aerial. A suitable small capacitor between FM aerial and L1 would block SW and not affect VHF. Would work to 30MHz with suitable cap and pair of coils.
I've actually got or had a radio with that IC. I had the datasheet already.
For MW Pg 11
1 & 2 is 106 turns
3 & 4 is 7 turns
So for LW about 210 turns = x4 inductance which would be only reduction to 400 kHz ) and also padding capacitor to lower frequency more and reduce tuning ratio. So possibly 250 to 300 turns. secondary would be about 14 to 20 turns.
IC Pin 2 is AM in (from smaller winding via switch. IC pin 4 is AGC so MW & LW secondary coils can be common
One side of tuning cap is to common/OV, the other side should go to coil primary of LW or MW via switch. One end of each primary coil goes to common/OV>
See page 9.
You can put a three way switch and do SW band too. A trimmer in series with tuning capacitor rather than to 0V. Maybe 20 turns to 5 turns on a small ferrite and capacitor to FM aerial. A suitable small capacitor between FM aerial and L1 would block SW and not affect VHF. Would work to 30MHz with suitable cap and pair of coils.
