Controller 4.0

Controller designed for Amateur Radio LDMOS Amplifiers built at home. Based on powerful firmware on board Arduino Nano, it shows precise measurements, delivery voltage sequences, all protections for LDMOS devices, touch screen switch controls and functions. It also incorporates the Rf Band Decoder that selects the Low Pass Filter automatically without additional cables.

The RF Band Decoder is one of the most attractive options . No more incidents by forgetting or not changing the band selector. You do not need to find the specific radio interface for amplifier tracking. Video

RF Band Decoder Circuit integrated in the controller

Signal sample for band decoder with 22 pF coupling capacitor at the 50-ohm Att input:

The code for Arduino Nano is programmed by Alexander RZ1ZR. For the operation of this controller it is necessary to connect a Nextion Enhanced NX8048K070 7.0 “or Nextion Enhanced NX8048K050 5.0” screen. The Nextion device must be loaded with RZ1ZR firmware through the SD card port. Request the firmware Here 


Circuit for Arduino Nano integrated in the controller

All necessary protections for LDMOS devices

High temperature.
High current.
High voltage.
High output power.
High SWR. LDMOS devices are usually very robust and support SWR 65: 1 such as BLF188XR / MRF1K50H. But this is not enough to extend the life of the linear amplifier for Ham Radio since some components can overheat and break. Or worse, we forget to select or connect the antenna. The video shows the precise protection when SWR> 2 Video
Continuous carrier detector. Some amplifier designs can withstand long cycles with an output of 1300 watts in SSB. But a continuous carrier requires twice the effort. Additional heat sink, huge ferrite cores and duplicate components, this increases the cost of home manufacturing. The video shows a protection for continuous carrier> 8 seconds> 700 watts. Video
Wrong Band Selection. Operating an amplifier in attenuation frequency can be fatal. The video shows the protection when the 80 meter filter is selected manually while the radio is operating at 40 meters. In addition, protection is also activated if the Low Pass Filter is damaged. This function does not need a SWR meter at the filter inlet.  Video

All protections were tested and guaranteed with genuine components, never tested with fake components. 




The nominal voltage of the controller is 53v and does not need a separate 12v source. The controller incorporates a Step Down 60v-12v DC Fulree FJ60D12C3 3 Amp device:

Voltage Driver




While the PTT is up the controller does not deliver voltage to the Power Unit (output 53.7v TO PW. UNIT) either when an alarm is activated. The switching device is BTS50085-1TMA:

Heat dissipation on the board for BTS50085-1TMA will support: continuous carrier <22 amps and SSB <37 Amps>. For currents> 37 amps, place two BTS50085-1TMA devices on the board (optional foot print available). It is recommended to place a non-conductive silicone heating pad on the bottom.


All IDC connections are compatible with current KM3KM designs.

Board Connections

The voltage sequence prevents the relays from burning with an RF arc. Due to the mechanical movement of the relays(GRL2)  the delay is 10 milliseconds when the PTT is down, then 12 V Bias and  drain voltage is delivered 20 milliseconds after PTT, total time 20 milliseconds (On Air) in Manual Mode.

The 8-bit PIC micro controller detects the frequency and connects the LPF relays, after 15 milliseconds it connects the 12 V Bias and  drain voltage, total time 25 milliseconds (On Air) in Automatic Mode.                                                                                                                                                                                                                                   I measured the delays with an oscilloscope, but this effect can be seen with a high speed camera. The led indicates the voltage delivery after  relay sound. Video

Note that in SSB mode the radio will not emit RF without modulation, 200 milliwatts are required to detect the operating band. Most radios inpulse RF with PTT click, this is enough.

Manual Band Select time sequence:

Auto Band Select time sequence:




Power Unit IDC

Connection to control the Power Unit. Bias voltage 12v 200mA. DS18B temperature sensor. GND


To set the bottom bars automatic selection:

1-Press and hold SW1.                           

2-Turn on the controller.

3-Apply Rf in the desired band.

4-With the SW1 / SW2 buttons move the bottom bar of the display and stop it in the correct band.

5-To save values, press both buttons simultaneously.

6-Repeat this operation for each band.

This setting is only to move the lower bars of automatic selection, the filter segments are predetermined and will not change. (This setting is only necessary for display errors.)


Connection of Latching Buttons with LED. The POWER button is directly connected to the ON SW terminal, it is used to turn on power supply with low voltage. The OPERATE button connects the 12v of the Bias controller circuit and enables the PTT line, if the button is disconnected the amplifier will be in Standby mode. Both connectors have an output for the LED voltage. The voltage may change depending on R9 and R31.


The connection is directly to the POWER button, it is used to turn on the power supply with low voltage.

Nextion Display

Port to control the Nextion display. Voltage 5v 900mA


Connection to control LPF (Open Collector). Do not load the segment outputs to more than 80 mA 15V. LPF Relay must have an activated diode for reverse currents.


Connection for Antenna Relay (Open Collector) PTT and ALC Do not load Relays outputs at more than 120 mA 15V.

53.7v to

Pw. Unit Con

Controlled voltage output to the Power Unit. Do not charge the output at more than 35 Amps (1x BTS500850), 45 Amps (2x BTS50085-1TMA)


Pw. Supply Con

General supply voltage. Max input DC 57V.


Connection to fans or Water Pump 12V. Do not load both outputs to more than 900 mA (450 mA x 2). Note- No PWM


The fans turn on from 0 to 100% Automatic/Manual speed. JP1 activated (recommended) fans turn on permanently 30% at 100% automatic / manual speed. Do not use this option when the load is more than 350 mA. Note- No PWM

RF Band D.

It is sufficiently high frequency voltage from ~5V for stable operation, which corresponds to the

power of 0.5 W at impedance of 50 Ohm.


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