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Radio FM

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Edmond

Member
FM reciver

:D I don't know what do you want to transmit. In case of mono audio signal I suggest you the TDA7000 Philips radio receiver. You have to use it with external 30..80 MHz RC or XTAL oscillator for fixed freq. If jou wants to tune it, then use RC OSC with varicap diodes. For transmitter use a simple RC oscilator, wich can be modulated with varicaps in FM. If you need I can send you a schematics.
 

TheOne

New Member
Re: FM reciver

Edmond said:
30..80 MHz RC or XTAL oscillator for fixed freq. If jou wants to tune it, then use RC OSC with varicap diodes. For transmitter use a simple RC oscilator, wich can be modulated with varicaps in FM. If you need I can send you a schematics.

RC or LC? RC on 30-80MHz will be a real challenge!
 

TheOne

New Member
Zener_Diode said:
Can someone suggest me chips for reciving and transmitting a fm radio between 30-80Mhz.
actually I thing one PLL chip that can work on 85-90Mhz will be fine to me.

thanks ahead....

Look at **broken link removed**

The BH14XX devices should suit your needs. The one version you can program with dip switches, without using a micro
 

TheOne

New Member
You want narrow band and not wide band. According to the datasheet you can disable the stereo part with a switch. I think if you limit the deviation (there is a pot on the diagram to set this) to 10-15kHz you should be able to receive it OK on a narrow band receiver.

It looks like the output will be low from this chip. About -7dBm. I think you will need some amplifier to get any distance further than about 20' from it.
 

TheOne

New Member
This chip is only a transmitter. You need another receiver. What are you trying to do, make a transceiver?
 

TheOne

New Member
Zener_Diode said:
where and how can I choose my BW???
and if I will put a 50 om antena, will my sensitivity be around 0.6uV?
and how can I calculate all caps???

You need to download an application note on how to use the device and calculate the values.

Using a 50-Ohm antenna will cause a mismatch for the chip which appears to have a 75-Ohm input impedance.

0.6uV with acceptable level of distortion ...I don't think so. Maybe with a RF preamp.
 

TheOne

New Member
The TDA7000 was made obsolete by Philips so I am not sure where to get it. Search Google, that's all I could do.
 

zachtheterrible

Active Member
hey zener. i made a tda7000 receiver. here is the link for all my questions and stuff as i was building it: https://www.electro-tech-online.com/threads/basics-of-electronics.11866/

and here is the link of where i got the plans: **broken link removed**

i didnt think that the TDA7000 was all that great of a receiver. the stations that i got w/ it also came in on a clock radio just as good. maybe i just wasnt building it right, i dont know. i am still looking for a very sensitive FM radio for my FM bug that i built.
 
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pike

Member
I built a tda7000 kit available at my local store. The selectivity is excellent as it is a full super het design. MOving the capacitor 1/2 of a degree caused the station to shift.

It was too selective, in other words!!! Sensitivity on the other hand was down compared to my good' ol sony walkman. especially in the lower frequencies for some reason.
 

zachtheterrible

Active Member
wut kind of capacitor were u using pike? i used a 2-18 pf cap and i was able to hone in on a certain frequency quite nicely. if i'd used a 0-3 pf cap, i would get an even smaller deviation.
 

pike

Member
60-160pf

I know thats a huge range right there. It still doesn't cover the whole fm band though. Only about 3/4 of it. If I Wanna move it up I have to unwind the ferrite slug in the coil.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Zener_Diode said:
as I understood the tda7000 is good for 75ohm antena, I need to make it for 50ohm antena, how can I do it???

I wouldn't worry about it, I doubt it's got any low impedance matching inside the chip - it's probably only specified at 75 ohm because that's what's used for FM radio aerials.
 

TheOne

New Member
Doing some matching may not be a bad idea as can be seen from the plots. Without matching the there's quite a bit of loss and bad return loss.

With matching the input loss is 4dB less and the return loss very reasonable in the passband. Also the added selectivity will make a difference in performance.
 

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Nigel Goodwin

Super Moderator
Most Helpful Member
TheOne said:
Doing some matching may not be a bad idea as can be seen from the plots. Without matching the there's quite a bit of loss and bad return loss.

With matching the input loss is 4dB less and the return loss very reasonable in the passband. Also the added selectivity will make a difference in performance.

How did you arrive at the circuits and plots?, there's no suggestion in the TDA7000 datasheet that the input impedance is 75 ohms? - which is what I suggested in my pervious post.

The internal block diagram shows it has a balanced input, with a 700 ohm resistor from each input to a 1.4V reference. The second input is simply grounded via a capacitor in the application note.
 
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