ba1404 clock signal , help

Hi guys. I build a FM transmitter based on the ba1404 chip. The problem arises because this chip need a 38Khz crystal for produce a subcarrier signal for the stereo transmition, but that crystal is hard to find. To solve it i programed a PIC16f84 to generate the 38 Khz signal and, depending of what crystal use for the PIC, i could reproduce the 38Khz fecuency more or less exactly. (For example wuth a PIC runing on a 4MHZ crystal a can generate a 38,4 Khz signal). What accurate such signal have to do?

Thanks, and scuse my english. Cheers.


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** Within 2% should be fine - FM receivers have a small range over which they will lock on to the 19kHz pilot tone.

I have no doubt FM broadcasters keep the pilot frequency within a few ppm.

BTW Get yourself a spell checker.

..... Phil

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Phil Allison



Hi, thanks for the response. Yesterday i had the oportunity of measure the circuit with an osciloscope. The method of injecting the signal externaly seems to work. But I had a problem, because when conect the circuit and transmit audio trough it, it seems to be that transmit in stereo, but the L channel is not transmitted (while the right yes). I make a test: I connected R to 0V and L to a sine wave and something appears at the pin 14. But if i make the opposite( connect L to 0V and L to a sine wave) nothing happens.

I have three questions:

1) The signal that must appears at pin 14 is simply the conmutation between the channel R and the channel L ? (O maybe that signal filtered , but basically the multiplexing between the two channels, is correct?)

2) If I apply 0V to pin 5 (the "clock in") the signal present in pin

14 must be one channel and if conects nearly VCC to pin 5 in pin 14 appears the other channel, thats rigth?? Since when I transmit in stereo (though the R channel is not transmitted and I transmit only the L) the audio is listening something noisy, but if connect the pin 5 to 0V is clean.

3)Is possible that I have burned only the multiplexer?

4)Another story: the input impedance is 540ohm typically (ba1404 datasheet). I surprised, i think that it must be much more higher; that is the input impedance in pin 1 and pin 18?

5)Finally: I understand I have a poor level of english, so I thanks to you that you alert me ("BTW Get yourself a spell checker"), and that read the posts. two quiestions: * spell checker is for ortography not? But I think I have a poor level of Grammar also, is corect? * Whats means "BTW" ?


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On Sun, 28 Sep 2008 17:32:53 -0700 (PDT), gula put finger to keyboard and composed:

I don't know where you are posting from, but this crystal is available in Australia for $4:

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FYI, several years ago Silicon Chip magazine published an FM transmitter kit:

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- Franc Zabkar

Please remove one \'i\' from my address when replying by email.
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Franc Zabkar

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