Dave Robinson WW2R
First published in Feedpoint June/July 2000
Introduction
These amplifiers were most prevalent around 10 years ago, but still appear at Hamfests today. I have seen 3 in the last year, Including Dayton 2000. My sample was bought at Microwave update in 1991 in Arlington, the original seller recognised his handwriting on the case a few weeks ago!
Interest in the amplifier was recently resuscitated by deciding to upgrade from my old KK7B 1296MHz IF transverter with TWT to a 13.8V solid state 144MHz design using the DB6NT transverter and local Oscillator.
Specification of the Amplifier
From the original military specification sheet:-
Frequency range: 5925-6425MHz
Input Voltage +11.4 to 12.6V 4.5A maximum
-11.4 to -12.6V 0.1A maximum
Power Output 36.5dBm minimum with +/-12V supply and 0dBm drive
RF Sample Output -37dB +/- 5dB
Power monitor -4.0V (adjustable) into 10k load
size 11.4 x 2.7 x 1 inches
Weight 4.6lbs nominal
Connections
One end of the amplifier has a single SMA connector which is the input. The opposite end has 2 SMA connectors, the one being coaxial with the input is the RF output, the other being the RF sample.
The following Table refers to the pinouts of the 9 pin black plastic connector terminating the cable attached to the amplifier:-
| Pin | Cable | Function |
| 1 | Black | GND |
| 2 | Red | +12V |
| 3 | Orange | -12V (Gate Bias) |
| 4 | No Pin | |
| 5 | Red | +12V |
| 6 | Green | RF POWER ALARM |
| 7 | ||
| 8 | Brown | OUTPUT MONITOR |
| 9 | White/Orange | -12V (enables RF POWER OUTPUT ALARM) |
Power Supply
From the specification a power supply to give +12V at around 3A and -12V at around 100mA is required. The same configuration as the power supply for the Qualcom 10GHz Omnitrak Amp was used, with the voltage programming resistors adjusted for the new voltages. Notice that IC2, a LT1083 is uprated to a 5A device from the 1 Amp LT1086 used in the 10G version. To give some room for the voltage drop along the supply cables, the unit must be powered from 13.8V. This is also the reason for choosing 11.8 rather than 12V as the supply voltage value, The Power output is unaffected by the change. Figure 1 shows the circuit, Figure 2 shows the PCB layout, Figure 3 shows the component overlay. Notice the components are mounted on the track side of the board.
Figure 1: Circuit
