BH1417 Stereo PLL FM Transmitter

  Parts:
1x BH1417 - Stereo PLL Transmitter IC (Case SOP22)
1x 7.6MHz Crystal
1x MPSA13 - NPN Darlington Transistor
1x 2.5 Turns Variable Coil
1x MV2109 - Varicap Diode
1x 4-DIP Switch
ANT - 30 cm of copper wire

1x 22K Resistor
7x 10K Resistor
1x 5.1K Resistor
2x 3.3K Resistor
1x 100 Ohm Resistor		 1x 100uF Capacitor
3x 10uF Capacitor
2x 1uF Capacitor

1x 47nF Capacitor
3x 2.2nF Capacitor
1x 1nF Capacitor
1x 330pF Capacitor
2x 150pF Capacitor
1x 33pF Capacitor
2x 27pF Capacitor
1x 22pF Capacitor
2x 10pF Capacitor

  Technical Specifications:
Supply Voltage: 4 - 6V
Transmission Frequency: 87.7 - 88.9MHz, 106.7 - 107.9MHz (200kHz steps)
Output RF Power: 20mW
Audio Frequency: 20 - 15KHz
Separation: 40dB
Power Consumption: 30mA





About BH1417 Stereo PLL FM Transmitter
 

This is the latest BH1417 FM Transmitter design from RHOM that includes a lot of features in one small package. It comes with pre-emphasis, limiter so that the music can be transmitted at the same audio level, stereo encoder for stereo transmission, low pass filter that blocks any audio signals above 15KHz to prevent any RF interference, PLL circuit that provides rock solid frequency transmission (no more frequency drift), FM oscillator and RF output buffer.

There are 14 possible transmission frequencies with 200KHz increments that users can select with a 4-DIP switch. Lower band frequencies start from 88.7 up to 89.9 MHz, and upper band frequencies start from 107.7 up to 108.9 MHz.

BH1417 can be supplied with 4 - 6 voltage and consumes only around 30mA, providing 20mW output RF power. BH1417 provides 40dB channel separation which is pretty good, although older BA1404 FM Transmitter chip provides slightly better 45dB channel separation.

BH1417 is only available in SOP22 IC case so 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 transmitter on a small PCB.

BH1417 chip may also be used a stand alone stereo encoder. The advantage of that is that you have full freedom of using a transmitter & amplifier of your choice. You will still have a pre-emphasis, limiter, stereo encoder and low pass filter in one small package because very few external components are required for these blocks. PIN 5 is MPX output that can be directly connected to an external FM transmitter through a 10uF cap.


BH1417 Block Diagram
 
Main blocks of BH1417 chip are; pre-emphasis, (audio level) limiter, stereo encoder (MPX), PLL circuit, oscillator and RF buffer.




Frequency Selection / Calibration
 
Frequency selection is very straight forward. Simply select transmission frequency at which you would like to transmit, set the combination for 4-DIP switch and BH1417 will immediately tune to that frequency. If you can't hear the transmitted audio signal on your FM receiver then re-adjust 2.5 turn variable coil until you can hear the signal.
As a test to see how PLL is working you can use a laboratory power supply to vary the voltage supply from 4 to 6V. While doing that BH1417 will automatically vary the voltage for MV2109 varicap diode making sure that there's no frequency drift.

S1
S2
S3
S4
Frequency
ON
ON
ON
ON
87.7 MHz
OFF
ON
ON
ON
87.9 MHz
ON
OFF
ON
ON
88.1 MHz
OFF
OFF
ON
ON
88.3 MHz
ON
ON
OFF
ON
88.5 MHz
OFF
ON
OFF
ON
88.7 MHz
ON
OFF
OFF
ON
88.9 MHz
ON
ON
ON
OFF
106.7MHz
OFF
ON
ON
OFF
106.9MHz
ON
OFF
ON
OFF
107.1MHz
OFF
OFF
ON
OFF
107.3MHz
ON
ON
OFF
OFF
107.5MHz
OFF
ON
OFF
OFF
107.7MHz
ON
OFF
OFF
OFF
107.9MHz




Frequently Asked Questions
 

This is list of answers to questions that I have received through an e-mail so far. If you should have any other questions please don't hesitate to e-mail them to me.

What is the range of BH1417 Stereo FM Transmitter?
Range of the transmitter depends on many factors.
a) Length and type of the antenna (the longer the better, copper will radiate radio waves better than aluminum)
b) Supplied voltage (6V Max power output)
c) Weather conditions (clear skies & no humid, greater distance)
d) Elevation above the ground (the higher the better)
e) Line of sight (no buildings or trees, greater distance)
f) Whether external amplifier is used

I would like to be able to transmit the music to greater distances. Can you provide any suggestions on how to modify the circuit?
You can connect an external amplifier based on the common 2N3866 / 2N4427 RF transistors. Please keep in mind that it is illegal to operate higher power transmitters in most of the countries without the proper license.


Where to get the Parts
 

If you are building the above Stereo PLL FM Transmitter and have trouble finding some of the components like BH1417, 7.6 MHz crystals, 2.5 turn high precision variable coil and MPSA13 darlington transistor we are distributing these components in our Electronic Store.

 

Build your own LC Meter and start making your own coils and inductors. This LC Meter allows to measure incredibly small inductances making it perfect tool for making all types of RF coils. LC Meter can measure inductances starting from 10nH - 1000nH, 1uH - 1000uH, 1mH - 100mH and capacitances from 0.1pF up to 900nF. The circuit includes an auto ranging and "Zero Out" function to make sure the readings are as accurate as possible ... [more]


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