ba1404 clock signal , help

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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.


Re: ba1404 clock signal , help

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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

Re: ba1404 clock signal , help
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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

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" ?


Re: ba1404 clock signal , help
put finger to keyboard and composed:

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

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

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

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