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Using FM radio in a digital high bit rate data link

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ahmad_abdulghany

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FM radio..A question..

I am trying to use the FM Radio IC tda7000,
(find its data sheet here: **broken link removed** )

The problem is i want to use it in a digital high bit rate data link

You may simpy notice from its datasheet that there's a 10kHz BW AF filter (LPF) as a last stage, that filter will limit the bit rate to about 9600 paud maximum..

I thought to increase bit rate by cascading another HPF with that filter as a compensation to it ... This HPF should have the same cuttof, or even lower cuttoff to get nearly white band (flat band) responce..

Do you think it's feasible method to make?

Also, how can i characterize the IC filter to be able to decide about the actual c/cs of the HPF to be designed?

I need comments
Thanks in advance,
Ahmad,
 

Re: FM radio..A question..

Your method will cause noise enhancement problems. You would be better off tapping the signal off before the amplifier and using an external one of the proper bandwidth.
 
Re: FM radio..A question..

flatulent said:
Your method will cause noise enhancement problems. You would be better off tapping the signal off before the amplifier and using an external one of the proper bandwidth.

Can i do this in the case of TDA7000?
 

Re: FM radio..A question..

Hmmm, 10 KHz is a little low. Most FM audio radios have a lowpass filter at more like 15 KHz. This is because they fold the band over at something like 19 KHz and use frequencies above that for the other side of the Stereo audio. So if you do not LPF the baseband stuff, you end up with one channel L+R spreading over into the L-R other channel, and you get garbage for audio.

ROHM makes a stereo chip that is good to 15 KHz, the BH1415F
 
Re: FM radio..A question..

biff44 said:
Hmmm, 10 KHz is a little low. Most FM audio radios have a lowpass filter at more like 15 KHz. This is because they fold the band over at something like 19 KHz and use frequencies above that for the other side of the Stereo audio. So if you do not LPF the baseband stuff, you end up with one channel L+R spreading over into the L-R other channel, and you get garbage for audio.

ROHM makes a stereo chip that is good to 15 KHz, the BH1415F

I need to get bit rate higher than few hundereds of Kbits/sec ( i hope in fact to achieve one or more Mbps)

Regards,
Ahmad,
 

Re: FM radio..A question..

the build in IF filter will keep you from having bit rates over 50 kb/s. For FSK, the signal bandwidth is about 3-4 times the bit rate.

You should try some form of 802.11 transmission. These modules are low cost.
 
Re: FM radio..A question..

flatulent said:
the build in IF filter will keep you from having bit rates over 50 kb/s. For FSK, the signal bandwidth is about 3-4 times the bit rate.

You should try some form of 802.11 transmission. These modules are low cost.

Sorry, but what's the 802.11 transmission?!

Also, I still need to know for TDA7000, is it IMPOSSIBLE to get bit rate higher than the limit i told about above?! I hope you see its datasheet and tell me..

Thank you very much for help,
Ahmad,
 

FM radio..A question..

that filter will limit the bit rate to about 9600 paud maximum.

You mean it will limit the symbol rate to 9600 baud. Bit rate and baud rate are
not the same thing.

the build in IF filter will keep you from having bit rates over 50 kb/s

Not necessarily. It depends on the coding scheme and the signal to noise ratio.

FSK is one bit per symbol. Carrier at lower frequency =0, carrier at higher frequency=1

In theory you could use four different carrier frequencys to represent 00,01,10,11
or take it further and use eight, sixteen or more carrier frequencys.

In practise this rapidly gets difficult to decode. By the time you have a DSP in
your receiver might as well throw away the cheap FM IC and use somthing like OFDM.

Shannon's law gives the maximum possible bit rate that can pass through a channel
of a paticular width and s/n ratio.
 

Re: FM radio..A question..

I have been trying to implement the sub-carrier modulation for FM radio.
The standard of RDS gives 1.2 kbps, and DARC gives 16kbps.
You might wanna look at those.
Still you can let the occupying audio have its space for broadcasting, too.
Look at FM demod IC SA605 for larger bandwidth.
 

Re: FM radio..A question..

taka_taka said:
The standard of RDS gives 1.2 kbps, and DARC gives 16kbps.
You might wanna look at those.
Still you can let the occupying audio have its space for broadcasting, too.
Look at FM demod IC SA605 for larger bandwidth.

What are these two standard? I want to know about them,

Concerning that IC, i got its datasheet, but it's not available here at my place, TDA7000 isn't also available here, but i already got some parts of it!
 

Re: FM radio..A question..

This site might be helpful for RDS:
**broken link removed**

DARC = Data Radio Communication standard
It has higher bit rate, about 16kbps
 

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