[MOVED]Digital FM radio tuner.

[slnuwan]

Dear All,

Please help me to study about fm digital radio tuner. I went through internet and could not find any related thing to digital radio tuner and how it works.
So kindly help me to study about this.
I have an idea of analog FM tuner and its tuning method. Normaly its working with variable capacitor and inductor resonance circuts woks and cct is tuned. But I do not know how digital duning woks on a FM receiver cct.
Please help me to find any book or PDF document on this.

I had a sony mini- anudo system ant its radio tuner is not working.
I tried ti retify it in my best and I could not find the issue.
So I decided to replace the tuner with any other tuner cct.
Can it be done? please advice me on this also. Thanks all.

Nuwan Mahesh,
(Sri Lanka)

 

[sky_123]

Re: Digital FM radio tuner.

I don't think you can replace with another cct and expect to integrate it into the same controls as the rest of the audio system easily,
especially if it is all on the same board.
It would be more of a challenge than to just pay someone to fix the existing tuner.
If you wanted to go down the road of building your own digital tuner, then it is no different than an analog tuner, except that you can use a thing called a varactor diode
to adjust the capacitance, via a DAC. But the other thing you will probably need (different to analog tuners) is a PLL, to ensure the frequency
is correct and stable.

 

[slnuwan]

Re: Digital FM radio tuner.

SKY_123 thanks for the update....

One of technician tried to fix that tuner and he also could not do it.

Can you please share some sample cct of how engaging varactor diode in tuning and some block diagram of these ?
It will more help full to undestand.

Please help me I realy realy like to study about tuners.

 

[sky_123]

Re: Digital FM radio tuner.

Something like this is reasonably simple : https://www.aaroncake.net/circuits/fm_radio_circuit.asp
You can see D1 is the varactor diode, and R3 controls the voltage to it. You could use a DAC instead of R3.
Note this cct does not use a PLL, so it is hard to know the precise frequency to display it.
A PLL radio can be made using something like the diagram at https://hem.passagen.se/communication/dtmfrec.html
You can see the circuit there uses the SA616 for mixer and VCO, and another ic (a bit obscure one) as a PLL.
National Semi and Analog Devices has PLL ics.

 

[wa1kij]

Re: Digital FM radio tuner.

Tuned circuits tend to be unstable at VHF frequencies. You could control a varactor with a voltage, but the frequency would change with changing environmental factors, especially temperature.

Digital FM tuners work the same way as analog ones. They are superheterodyne receivers that demodulate the FM signal at (usually) 10.7 MHz. A local oscillator generates a signal 10.7 MHz above or below the desired frequency. Analog tuners adjust the local-oscillator frequency with a variable capacitor. In digital tuners the local oscillator is a VCO operating in conjunction with a PLL. The receiver's display shows the radio station's frequency, not the local oscillator frequency which is what the PLL actually locks onto.

 

[slnuwan]

Re: Digital FM radio tuner.

SKY_123 and wa1kij thanks for your posts.
I got a huge idea on this.

If someone has any more smple cct and notes kindly share with me

Thanks all.
Nuwan mahesh,