At last, a weekend and free time.
I decided to have a look at the Spectrian amplifier I bought a couple of years ago from 'Pyro Joe' on e-bay, while QO-100 was still being assembled. The board comes mounted on a 1/4 inch (6.25mm) thick Aluminium heat spreader, so my first job was to mount it onto a decent sized heat sink. Being of US design, M4 screws were just a little too large to fit, but 4BA were perfect. A little drilling and tapping later and the the amplifier was ready for a DC test. The amplifier has a 14 pin connector with 4 pins for V+ (12V) 5 connections for ground or 0V , one ground to transmit pin, another which needs 24V input at 25mA and a pin which has a DC output voltage from a PA temperature sensor.
With 12.2V and 24V @25mA applied, I connected a 30dB attenuator to the output and 50 ohms to the input. When the enable pin was grounded the supply current increased from a few milliamaps to 6.6A. - If this device is Class A, that should be fine. Now it was time for some for some RF input
RF testing used a signal on 2400.50MHz at levels from -6dBm to +11dBm.
With 12.2V and 6.6A standing current, I hoped that a class A amplifier would not need much more current across the range of input powers. Unfortunately testing shows the amplifier draws higher DC currents as you increase power. Clearly the PA stage is not class A after all. I wonder if efficiency can be improved. Overdriving this amp could be very expensive as it does not appear to go into compression...It just consumes more DC power and it can't do that forever.
RF Input dBm |
RF Output Watts |
Apx. DC Current |
-6 | 0.625 | 6.6A |
-3 | 1.2 | |
0 | 2.25 | |
+3 | 4.2 | |
+4 | 5.2 | 6.8 |
+5 | 6.6 | 7 |
+6 | 8.2 | |
+7 | 10.9 | 8 |
+8 | 13.5 | 9 |
+9 | 17.5 | 10 |
+10 | 21.5 | 11 |
+11 | 26 | 12 |
73 David G0MRF