circuit design for multiband auto tunning radio

[litu]

friends,
i want to make an project in my academics.
i.e. MULTIBAND (AM/FM) radio with AUTO TUNNING.
i know the design procedure for the radio circuit but i have no idea
about the design of the auto tunning circuit that will scan both AM
and FM bands.
so please any body having any idea share with me.

thanking you

with regards
Pradipta

 

[Joe G \(Home\)]

use varactor diodes to take care of the capacitance tuning for the RF, VCO.

have station detector circuit that detects when tuned to the station....
(without false triggering).

Simple.

Joe

 

[JosephKK]

litu [email protected] posted to sci.electronics.design:

friends,
i want to make an project in my academics.
i.e. MULTIBAND (AM/FM) radio with AUTO TUNNING.
i know the design procedure for the radio circuit but i have no
idea about the design of the auto tunning circuit that will scan
both AM and FM bands.
so please any body having any idea share with me.

thanking you

with regards
Pradipta

Simple, factor for the common parts versus the band unique parts and
build it. Dithering will provide the autotuning information.

 

[Frank Raffaeli]

use varactor diodes to take care of the capacitance tuning for the RF, VCO.

have station detector circuit that detects when tuned to the station....
(without false triggering).

Simple.

Joe

(Assuming analog transmission): It's not that simple. Use a PLL to
tune the Local Oscillator to each frequency in the band. When the RSSI
(received signal strength indicator) reaches a pre-determined
threshold, stop at that frequency. Use a counter to count the I.F.
This makes sure the received signal is on frequency. False stops are
still possible but less likely.

If you don't have access to the RSSI signal, you will need to convert
your I.F. signal amplitude to a log scale for the thresholding
measurement.

This is how we did it in the late 80's.

Frank