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The 6M-1K2 designation, indicates the amp works on the 6 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 50 to 100W output on 6M, the gain of the device must be reduced 15 dB or less per part 97
FCC rules. 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 relay and then through
a high power vacuum relay, through the internal SWR bridge 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 1200 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 transceiver but can also be keyed with a foot switch. A built in 15 to 20 millisecond delay al-
lows the relays to close before a +2.8 VDC bias voltage is applied to the gates of the device.
When “keyed up”, 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 a drive of 5W will cause the amp to produce 100+Watts. On 6M, 100W 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 drain current typically from 36 amps down to about 30
Amps and reduces the output slightly to 950 to 1050 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 is split and one part passes through a 3 Amp fuse on the rear panel. this 50V DC is
sent to 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 0.005 ohm
resistor in the drain lead of the device. The voltage drop across the 0.005R 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, and
secondary bias control for JT, AM, or FM mode of operation.
The RF drive power from a transceiver enters through an “N” female connector on the rear panel and jumpers through a
THEORY OF OPERATION
OVERVIEW
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