TDA 7000 FM radio can't tune in any station

[berkekrkn]

Hello everyone,

3 weeks ago I decided to build a FM reciever with my TDA7000 chip. ,The circuit is above, however I can not connect to any radio stations. I can hear only weird sounds.

I've built the circuit on a breadboard (to check if it is working). But as I said I can't hear anything except weird sounds. My friend told me that I should solder the circuit on a copper plate rather than using breadboard because jumper cables create capacitance. Is this true ?

Also I am really confused with the antenna. Can I use a simple copper wire ( if yes how long should it be ?) or do I need a professional thing ?

The last question: Can I use BB105 varicap diode instead of BB505B ?

 

[Audioguru]

The capacitance between the wires and rows of contacts on a breadboard causes problems when a circuit uses a frequency higher than a few kHz. FM radio is ten thousand times higher. The TDA7000 IC is very old and had very poor performance. I can buy a cheap Chinese radio for $1.00 at The Dollar Store that uses its replacement IC, the TDA7088 and its performance is also terrible. The radio comes with earphones and a battery that are worth more than the cost of the radio, so the garbage radio is free.

 

[73's de Edd]

Sir berkekrkn . . . . . . . .

Read up on the 7000 chip utilization in this writeup and expect to use the its PCB construction
they employed in order to get proper RF operation.

As AG mentioned, being built on a breadboard and all spaced out and poorly RF bypassed just will not even start to cut it at FM frequencies.

Reference to:

http://x01a4.net/dirc7/elec/am-fm-radio.htm





73s de Edd

 

[Audioguru]

The article has an error, it says the LM386 power amplifier is set for a voltage gain on 20 and wrongly says it is 40dB. A gain of 20 is actually a gain of 26dB. A voltage gain of 40dB is a gain of 100.