I recently got this e-mail about the atu: and the position of the capacitor:
"To create a variable capacitor insulated from the ground (chassies) is a "piece of cake"! This task involves adding two or four ceramic pillars for the variable capacitor. The obvious advantage is that the tiny link coil is now grounded, and in addition, the radio equipment, TX/RX, is "DC insulated" from the Antenna Tuning Unit, a small price to pay for additional safety of the equipment. 73 from Bengt, SM6APQ"
A smaller version for the 20 to 10m band is also shown below. I have used wire threaded into 1/4" plastic tubing for the coupling coil. When this is wound round the larger coil it provides spacing between the two sets of coils.
Set the transmitter to low power while making all changes to the ATU while adjusting for lowest SWR. In use set C2 to half way and carefully tune C1 till there is a dip on the SWR meter. This will be quite sharp so if possible use a reduction drive on C1. Then adjust C2 and C1 alternatly to get the lowest (1:1) SWR.
Instead of using switches (which could introduce extra capacitance and loss) I used bananna (3mm) plugs and sockets for connecting the antenna and the capacitor. This gives a lot of fexibility for trying out various combinations of connections.
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