BH1415 – Stereo PLL Transmitter
1x 7.6 MHz Crystal
1x 78L05 Voltage Regulator
1x 10K Resistor
3x 10uF Capacitor
2x 1uF Capacitor
2x 2.2nF Capacitor
1x 1nF Capacitor
2x 150pF Capacitor
2x 27pF Capacitor
Voltage: 6 – 15V
Audio Frequency: 20 – 15KHz
Power Consumption: 25mA
BH1415 Stereo Encoder
This is the
latest BH1415 Stereo Encoder design from RHOM that
includes a lot of great features in one small package.
It comes with pre-emphasis, limiter so that the
music can be transmitted at the same audio level,
low pass filter that blocks any audio signals above
15KHz to prevent any RF interference and crystal
based stereo encoder for stereo transmission.
BH1415 can be supplied with 6 – 15V voltage, consumes
only around 25mA while providing very sound quality
and improved 40dB channel separation. BH1415 is
only available in SOP22 IC case and this may be
an inconvenience for some folks. On the other hand,
because the chip is smaller than regular DIP-based
ICs it is possible to fit the entire stereo coder
on a small PCB.
BH1415 requires 7.6MHz crystal oscillator which
is pretty hard to find. The good news is that you
can find 7.6MHz crystal in our electronics online store.
Main blocks of BH1415
chip are; pre-emphasis, (audio level) limiter, stereo
encoder (MPX), PLL circuit, oscillator and RF buffer.
to Connect BH1415 Stereo Encoder to FM Transmitter
1) First test FM Transmitter
and make sure that an audio signal is properly
transmitted on your desired frequency. Once that
is done turn off transmitter and disconnect its
2) Connect left and right audio outputs from audio
source to the inputs of stereo encoder.
3) Connect stereo encoder’s MPX output to
transmitter’s input. Audio coax cable highly
4) Turn on transmitter, FM receiver and audio
source (making sure its audio volume is not too
loud), and apply 4-6 voltage to stereo encoder.
5) By now you should hear a stereo sound. Adjust
the volume of your audio source making sure an
audio signal is as clear as possible.
1. Can I replace
BH1415 with BA1404?
This is not possible because these two chips
have different internal architecture and pin
2. Can I use my own pre-emphasis circuit?
No, this is not possible because pre-emphasis
is built into BH1415 chip.
3. Stereo Encoder works but the transmitted
music comes out distorted. What can I do to
eliminate that distortion?
Make sure you are not over-modulating BH1415
inputs with higher / louder audio signals than
it can handle. Placing 10K stereo potentiometer
on audio inputs can help eliminate that problem,
although it is not necessary to achieve a good
sound quality. Lowering the volume of incoming
audio source should do it.
4. Stereo Encoder works but the transmitted
music comes out with noise. What can be done
to eliminate that noise?
Lack of proper filtering on your power supply
may be a problem. If power supply is being used
make sure that all the diodes on the rectifier
are bypassed with a 10n capacitors and that
your voltage supply is well filtered with at
least 4700uF capacitor.
5. Can I use my transmitter’s existing pre-emphasis?
Pre-emphasis can only be used before stereo
encoder’s audio inputs not after its MPX
output. Doing otherwise may produce undesired
results as MPX signal contains crucial 19KHz
PILOT signal needed for stereo decoding.
6. If I use a stereo encoder will any mono FM
receiver be able to receive the audio signal?
Yes. MPX stream that is generated by BH1415
contains both stereo and mono audio signals.
7. Is it true that stereo transmitters
require stronger power output comparing to mono
Stereo transmitters may require ‘slightly’ stronger
power output to achieve clear stereo sound on
the receiving part because transmitter has to
also carry out 19KHz PILOT signal without which
stereo transmission is not possible. If stereo
FM receiver does not receive a clear PILOT tone
it may change from stereo to mono reception.
to get the Parts
If you are building the
above stereo encoder and have trouble finding
some of the components like BH1415 and 7.6MHz crystals we are distributing these components
in our Electronic
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