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Making Your Own Transmitter Making Your Own Transmitter
Putting together a serious high power FM transmitter

This page deals with the problems of assembling together a serious high power professional quality FM stereo radio broadcasting transmitter with optional RDS capability. Our (MAX) kits will be used as an example as we feel these make it possible to put together a system with minimal effort. Several configurations will be presented and it is up to you to select the one that fits your needs best. This guide hasn't been updated for a while so we decided to finally change all old boards with new ones, the new ones make the process considerably easier.

1.) 15/25/40/50W stereo FM transmitter with RDS and PC remote control (USB, RS232 or Ethernet)
A 15W system will be presented here, with stereo encoder and optional RDS encoder. Optional RS232 remote control function will be included as well. Such system can be a building block of a much larger station. 25W can directly drive almost any high-power FM amplifier out there, up to 5KW and more. If the procedure below sounds too complicated you can also buy assembled ready unit here.

Required hardware components:
a.) 25W FM exciter module - our MAXPRO6015+/6020+/6025+/6050+ (updated)
here.You can also use the cheaper SE2000+, note that you can only adjust the DSP audio settings with SE5000 DSP+. You can also use our new SE6000 encoders.
c.) 30cm Maxlink cable to connect stereo encoder to MAXPRO 60xx - you can buy it here.
d.) RDS daughter board - RDSMAX or RDSIO5000+ RDS and IO board 
e.) Optional RS232/USB IO board+ available here. You can now also buy Ethernet interface and control your unit remotely via Ethernet or Internet.
f.) Stabilized mains power supply (12-15V/5A), a suitable model is available here towards the bottom of the page. MAX PRO 6050 requires 48V.
g.) Metal enclosure - your own or buy ours. On this page you can also find a small 40x40 12V fan, optional XLR connectors for stereo, maybe also On/Off switch.
h.) Also needed: some wire, short microphone coaxial cable, soldering iron, patience and a few hours of free time.

Wiring diagram for FM transmiter with stereo and RDS encoder

Block diagram of a 15W FM transmitter with stereo, RDS (not shown) and PC remote control (old exciter type shown)

Assembly steps:
a.) Mount the components into a metal case. 40x40mm fan, MAX PRO 60xx+ exciter board, SE5000+ stereo encoder, IO board. Don't install RDS just yet. You can find manuals for all these boards here.
b.) On SE5000 DSP+ stereo encoder set pre-emphasis jumpers to 50uS (EU) or 75 uS (Americas, Japan). Remove J10 and J14 jumpers. Connect MAXLINK cable from SE5000 to MAX PRO 6015+board.
c.) On MAXPRO6015+set pre-emphasis jumper (J2) to NONE. Install flat cable from MAXPRO6015+to the LCD module. Connect fan to FAN +- ports. Make sure MAXPRO6015+ is fixed to case with all screws and make sure to use METAL distancers, not plastic! You can use some thermal paste under heatsink, if you have it.
d.) If you want XLR audio input connectors, install XLR connectors as well. Note there are numbers 1-3 on the connectors that match numbers on 3-pin header on the PCB.
e.) Install RDS daughter board on top of stereo encoder, if desired (optional). Connect it to the IO board. Pin1 to pin 1 and pin 5 to pin 5. If you can't detect which pin is 1 try with ohm meter. Pin1 is connected to ground.
f.) Install audio coax between MPX out on SE5000 stereo encoder and audio input on MAXPRO6015+.
g.) Check all wiring again
h.) Pour yourself a glass of beer (or milk) and relax. You are done, time for a short break.

Finished unit with our rack, front

Finished unit with our rack, back

Setup and alignment:
a.) Before you turn the unit on make sure all connections are correct. Also make sure your antenna mounted correctly, cable is wired properly and tuned as per instructions. We recommend that you read the manual for MAXPRO6015+, there is a section dedicated to antennas, connectors and coaxial cable. Also check the manual for the antenna.
b.) Turn on transmitter and increase power to only 1/4 (25%). You can measure SWR (with a proper meter, not from the LCD display of the unit) and make sure everything is ok. On the radio you should hear either connected audio or total silence.
c.) There are only two things to align. First turn the audio modulation on MAXPRO6015+all the way to zero (direction -). Now while listening to your signal on the radio (set to same frequency as shown on transmitter LCD) turn modulation/audio trimmer on MAX PRO6015+until stereo indicator turns on. Turn it a bit more towards + and you are done. Connect some audio source and test your audio with ear-meter :)
d.) If you have RDS encoder, do the same thing there. Turn the trimmer to zero (no RDS indicator). Now slowly increase until you see RDS indicator turn on. Increase a little beyond this point and you are done.
e.) If your audio is weird, check pre-emphasis jumper on MAXPRO6015+board. It should be set to OFF!

Quick technical specifications:
- Power: 15W/20W/25W//50W
- Frequency band: 87.500 - 108.000 MHz
- Frequency step: 50KHz, PLL
- Modulation: FM, wideband
- Audio inputs: XLR and RCA
- Output antenna connector: BNC
- Power supply: 12-15V/5A stabilized or 24V/48V for 20W/25W/50W
- Extremely clean signal, complies and exceeds standards
- Qsonic PLL/VCO for excellent audio

2.) 300W stereo FM transmitter with RDS and PC remote control
A 300W system will be presented here, with stereo encoder and optional RDS encoder. Optional RS232 remote control function will be included as well. If the procedure below sounds too complicated you can also buy assembled ready unit here. or in a package including antenna, coaxial cable and everything else here.

Required hardware components:
a.) 15W FM exciter module - our MAX PRO 6015+
b.) SE5000 DSP+ stereo encoder - you can buy it here.
c.) 30cm Maxlink cable to connect stereo encoder to MAX PRO 6015 - you can buy it here.
d.) RDS daughter board - RDSMAX 4000+ mini
e.) Optional RS232 IO board+ available here.
f.) 300W/500W/650W/1000W/1400W FM amplifier module with DIGIAMP with integrated filter, metering, protections and DCDC stepdown regulator.
g.) DIGIAMP cable, available here.
h.) Stabilized mains power supply (110-240V to 48V), suitable models are available here towards the bottom of the page (SE600 for 300W amplifier module, RSP-1000-48 for 500-750W amplifier, RSP-2400-48 for 1200W-1400W amplifier module).
i.) Metal enclosure - your own or buy ours. On this page you can also find 80x80 48V fan, optional XLR connectors for stereo, maybe also On/Off switch and mains filter with switch, they all fit our box exactly.
j.) Also needed: some wire, short microphone coaxial cable, soldering iron, patience and a few hours of free time.

Wiring diagram for a FM transmitter with amplifier

Block diagram of a 300W FM transmitter with stereo, RDS and PC remote control (old exciter type shown)

Assembly steps:
First assemble the exciter and stereo encoder part, which is basically identical to the steps for 15W exciter in example 1 above. Note that you will be using this to drive a 300W amplifier so there are some changes there related to this amplifier and its mains power supply.
a.) Mount the components into a metal case. One fan is recommended for the exciter module, it does not have to be strong, just a simple 60x60mm or 80x80mm type. Another fan is recommended for the mains power supply. You may be able to combine them together and just use one. If possible place MAX PRO 6015 exciter board and SE5000+ stereo encoder in separate compartment, isolated by a metal wall. Don't install RDS just yet. You can find manuals for all these boards here.
b.) On SE5000 DSP+ stereo encoder set pre-emphasis jumpers to 50uS (EU) or 75 uS (Americas, Japan). Remove J10 and J14 jumpers. Connect MAXLINK cable from SE5000 to MAX PRO6015+.
c.) On FM exciter MAXPRO6015+ set pre-emphasis jumper to NONE. Install flat cable from MAXPRO6015 to the LCD module. Connect fan to FAN +- ports. Make sure MAXPRO6015+ is fixed to case with all screws and make sure to use METAL distancers, not plastic! You can use some thermal paste under heatsink, if you have it.
d.) If you want XLR audio input connectors, install XLR connectors as well. Note there are numbers 1-3 on the connectors that match numbers on 3-pin header on the PCB.
e.) Install RDS daughter board, if needed (optional). Connect it to the IO board. Pin1 to pin 1 and pin 5 to pin 5. If you can't detect which pin is 1 try with ohm meter. Pin1 is connected to ground.
f.) Install audio coax between MPX out on SE5000 stereo encoder and audio input on MAXPRO6015+.
g.) Check all wiring again and you can make a small break, the driving part of your 300W/500W or more watts transmitter is complete. You can connect antenna and test it. Once done it is time to move on connecting the amplifier module.
h.) Now install mains power supply in the the rack and be really careful while wiring the 110V/220V mains voltage, this is potentially lethal. Always make sure you do not touch any live wires when equipment is under mains power. Also note that sometimes live voltages can be present even after mains voltage is disconnected. Treat mains power supply with respect. Use a suitable switch with mains LC filter and a fuse, these ensure RF filtering, protection and power ON/OFF in a single device for convenience.
i.) Place and mount the power amplifier module with digiamp into the rack enclosure. Wire the +48V terminal to the mains power supply, preferably via a switch on the front panel.
j.) Wire the antenna output from MAXPRO6015+ to the power amplifier module input.
k.) Connect the DIGIAMP flat cable from the RF amplifier module to the MAXPRO6015+ exciter.
l.) Also wire the +12V from the digiamp power amplifier to the MAX PRO 6015+, this wire will provide power to the exciter and the stereo encoder.
m.) Set the jumper for drive power limit on MAX PRO 6015 to 1W or 2W (depending on your RF module, 300W requires about 6W max, 500W requires 2W, 650W requires about 5W).
n.) On the LCD display set ALC power limit value to rating of your amplifier, for example 500W. To enter this menu you will have to install jumper PGM (rot enc types).
o.) Pour yourself a glass of beer (or milk) and relax. You are done, time for a short break.

Finished unit with our rack, front

Finished unit with our rack, back (better photo coming soon)

Setup and alignment:
a.) Before you turn the unit on make sure all connections are correct. Also make sure your antenna is ok and well tuned. We recommend that you read the manual for MAXPRO6015+, there is a section dedicated to antennas, connectors and coaxial cable.
b.) Make sure power limit jumper is set appropriately (1W for example). Turn on transmitter and make sure power is set to zero. Since the power ramps up slowly you have 10 or so seconds to enter the menu system and change the power to zero, should it by some chance be set to max or non-zero value. Now slowly increase power while monitoring the output power with a power meter (not on LCD display, a real power meter). If the drive power is not sufficient change jumpers and add 1W of drive power (see manual).
c.) Keep increasing until you get close to the rated power (300W). Now that you've reached expected output power do not increase drive or you could destroy the amplifier.
d.) Now turn the POWER trimmer on the filter inside amplifier module until the LCD display shows correct output power (300W for example).
e.) Turn the SWR trimmer until the SWR alarm turns on, than turn it back until it dissapears + a bit more. Note that once the SWR alarm triggers it lasts for about 5 seconds so give it some time to dissapear.
f.) Now enter the LCD menu system and look for POWER LIMIT (last menu item). Set it to any power limit that you want to use, for 300W power amplifier set power limit to 300W. Exciter will now not drive the amplifier beyond 300W.
g.) RF amplifier setup is now complete, reduce powe to about 25%. On the radio you should hear either connected audio or total silence.
h.) There are now several things to align. First turn the audio modulation on MAXPRO6015 all the way to zero (direction -). Now while listening to your signal on the radio (set to same frequency as shown on transmitter LCD) turn modulation/audio trimmer on MAX PRO6015 until stereo indicator turns on. Turn it a bit more towards + and you are done. Connect some audio source and test your audio with ear-meter :)
i.) If you have RDS encoder, do the same thing there. Turn the trimmer to zero (no RDS indicator). Now slowly increase until you see RDS indicator turn on. Increase a little beyond this point and you are done.
j.) If your audio is weird, check pre-emphasis jumper on MAXPRO6015 board. It should be set to OFF!

You are now done!

Quick technical specifications:
- Power: 300W/500W/650W/1200W etc
- Frequency band: 87.500 - 108.000 MHz
- Frequency step: 5 or 50KHz, PLL (depending on module, 3000 or 4025+)
- Modulation: FM, wideband
- Audio inputs: XLR and RCA
- Output antenna connector: BNC
- Power supply: 110-240V mains voltage
- Extremely clean signal, complies and exceeds standards
- Qsonic II PLL/VCO for excellent audio


3.) PC based FM transmitter
This is about as cheap as you can get while keeping things relatively simple and reaching good quality. Complete PC based packages from 15W to 400W are ready for you, they are based on a PC card FM transmitter and a suitable FM amplifier.


If you have questions you can call us on Skype: pcs_electronics , you can also just click the Skype link on the right.
It is easy to get in touch with us, you can also click Live Support in the header of the page or you can e-mail us directly to email shown below:
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