[ARC5] My ARC-5 40 meter station

[Chris Bowne]

Great work Charles. To get the best loading and max your power output, try using the autotransformer matching network that Walt, KJ4KV published in an ER in Uniform column many years ago. It works very well, I use it on my command sets to get about 50 watts out on CW and 15 watts on AM, using the original BC-456 screen modulator and DM-33 dyno.  Consists of a parallel tuned circuit with the transmitter fed to a tap on the coil a few turns up from the ground end through a 150 pf series cap and the 50 ohm antenna fed off of a second coil tap a few turns above the transmitter input tap. I threw one of these together using a pi network coil set from a junker Eico 720 transmitter and a 200 pf transmitting variable.  As I recall the input tap is about 5 turns up from the ground end and the antenna tap 3 turns above that. Use a cap with relatively wide spacing as the voltage across the plates can get quite high at resonance.  I had arcing problems with a narrow spaced cap.  You tune for resonance with the autotransformer cap and then peak output with the command  set transmitter variable roller inductor.  With this setup your output should peak with the transmitter coupling control at about 2/3 of full travel,  I can't recall the ER issue the circuit appeared in but it was around 1989-1990 as part of a series of Walt's ERIU column on command sets. 

The circuit should also help with transmitter harmonic output suppression.

Sent from my iPhone

> On Feb 21, 2015, at 18:19, J Mcvey via ARC5 <arc5 at mailman.qth.net> wrote:
> 
> You get alot more than 8 watts out. The output was designed for low impedance (5-12 ohms ) a few hundred ohm capacitive 5-J200 antenna.Specs say you should exceed 40 watts in CW  and have a 15 watt voice carrier.Perhaps try using a 9:1 "unun"