Hi Roger

Okay bad choice of words. Try series... With the centre conductor of
both coaxes joined at each end you do indeed get 25 ohms.. "Parallel"
was more a case of describing the physical rather than electrical layout.

When you connect just the shields you effectively have a 100 ohm
balanced but shielded feeder with the two centre conductors being the
"real" transmission line. Also apparently good for placing inside a
metal pipe without it affecting the transmission system - but I am not
doing that.

And where the 50 ohm coax from the radio joins the bottom of the Q
section its shield goes to one wire and the centre conductor to the other.

Okay?

Roger Leone wrote:


My math says that 2 sections of 50 ohm coax in parallel makes a 25 ohm
feeder, not a 100 ohm feeder. Also, if your intention is to use the 2 coax
center conductors to connect to the loop feedpoint, where will the
differential mode currents which are necessary at the feedpoint come from?
And if you don't connect the coax shields to something at the feedpoint,
where does the current flowing in the shield go?