M2 2M-1K2 Operating Instructions Manual - Theory of Operation
6
The 2M-1K2 designation, indicates the amp works on the 2 meter Amateur Band and is capable of at least 1.25 kW of RF
output.
A single MRFE6VP61K25H Freescale™ LDMOSFET solid state device is the heart of the amplifier. Because most modern
Amateur transceivers have a 25-50W output on 2M, the gain of the device must be reduced so the input level is dropped to
4 to 5 watts so the device is not overdriven as fatal damage will occur. In “bypass mode” or with the Ready switch off and
the green LED un lit, the input RF passes through an input RF coaxial relay and then through the high power vacuum out-
put relay and out to the antenna. When the Ready/power switch is activated and the green LED is lit, the Amplifier can be
keyed and when driven with the rated RF drive, will amplify to at least 1250 Watts into 50 Ohms.
The Keying circuit requires a path to ground or near ground through the RCA connector on the rear of the amplifier. This is
usually accomplished by the driving transceiver but can also be keyed with a foot switch. A built in 15 to 20 millisecond
delay allows the relays to close before a +2.8 VDC bias voltage is applied to the gates of the device.
With no drive applied to the device it will idle at approximately 2 amps. This condition puts the device in a class AB1 state.
It is linear at this point so drive of 5W will cause the amp to produce 200+Watts. On 2M, 50W of drive, in SSB or CW mode
will allow the amplifier to produce 1200 Watts minimum. If the drive power is continuous such as with AM, FM or any JT
mode, the amplifier will sense this continuous drive level and after about 5 seconds, the bias voltage is reduced pulling the
amplifier closer to class C. This reduces the current drain typically from 36 amps down to about 30 Amps and reduces the
output slightly to 950 to 1000 Watt output.
When driven in the Single Sideband mode SSB or CW, the amplifier runs in the linear mode and delivers 1250W+peak to
the antenna. At full drive level the amp is at about the 1 dB compression point. Further drive will not cause much more
output, just more compression, possible distortion and less efficient operation.
A temperature sensor mounted next to the device, monitors the Celsius temperature of the huge copper “heat spreader”
the device is attached to. When the device temperature reaches about 40 degrees C, the two large but very quiet fans on
the top cover come on to push the warm air transferred to the aluminum fins out the rear of the amp. Another slightly
smaller, quiet bottom fan comes on and pushes cool outside air into and over the device and other RF components. This
warm air vents out the multiple rectangular openings at the rear of the main chassis. Over temperature occurs at 90 deg. C
and the amber LED will light. Cycling the READY switch re-sets the system.
A complete 1500W+ VSWR bridge is located just inside the RF output connector hear the rear panel. Forward and
reflected power is monitored and if the SWR reaches 2.5:1, the control system de-activates the amplifier and the AMBER
LED on the front panel will light. This “fault” condition can be “reset” easily by cycling the “Ready” switch or removing the
50 VDC powering the unit.
Operation in the fault condition is possible by turning off the ready switch and running in the “amp bypass” mode at the
drive level of your transceiver.
When 50 VDC enters the amplifier, it first passes through a 50 Amp fuse. Then the 50V DC is sent tor the regulator board
and accompanying power dropping resistors for fans and two voltage regulators where 13.6 volts is produced for the
control board functions and other relay operation. The 50 VDC is also sent through a 0.005 ohm power SMD resistor in the
drain lead of the device. The voltage drop across this “shunt” is sensed and conditioned to provide a linear voltage related
directly to the device current in a 1/10 ratio. 10 Amps of drain current reads out as 1.00 volts and 30 Amps of drain current
reads out as 3.00 volts. This circuit allows accurate FACTORY ADJUSTMENT of Idle current in either linear mode or JT,
AM, or FM mode of operation.
The RF enters through a medium power coaxial relay followed by the 100W power pad. After the pad the RF passes
through an impedance matching network and then into a coaxial transformer and on to the gates of the device. Bias
THEORY OF OPERATION
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