RF Circuits

This VHF linear amplifier works for 50 MHz frequency using 2SC1946A with power output about 20 Watt. It needs input 30mW and output 25W for 150 Mhz. It seems can be used for 144 Mhz without modification. There are Power IC and 2SC1946A with low-pass filter on the board.


Some Experiences
I have checked Mitsubishi Catalogue and found it is 175 Mhz(ft), 3W input - output 30W(at 13.5Vcc), Gp10dB. I reffered Linear Amplifier Hand Book for deciding capacitors and coils. I made PCB with cutting by cutter knife and removing by heat with solder tool.


After mounted all parts on the board, I tried to adjust SWR for input. Connect SWR meter between rig and linear amplifier and connect 50 ohm dummy load. Without power source for linear amplifier, I have to adjust SWR as it becomes lower (at least less than 1.5).

With adjusting TC, I could get about 20 Watt. And then I connected Omron Relay (G5V2) for input/output circuit and I adjusted again, after that I noticed power was less about 10W-12W.


I tried to adjust SWR to be 1.0 by changing coils. I have changed input/output coils from 2 turns to 3 turns and I could get SWR 1.0. After I got SWR 1.0, output power becomes about 25Watts but moduration was not good and seems self oscillation. I have changed input ATT with 6dB and after that moduration becomes good with 20W output.

Author: JO1ACW
Website: http://www.geocities.co.jp/Technopolis/7222