Mike,

You seem to be talking about situations like old time AM car radios, where
the feedline was really used as a shielded wire, and not a transmission
line. They got away with it, because the feedline was very short, and added
less than 100 PF of capacity.

When used as a transmission line, the line is terminated in, or at least the
same order of magnitude impedance as the the coax. The coax has both
capacitance, and inductance. So, if you connect a 50 Ohm antenna to 100 feet
of RG58 coax, the impedance you see at the other end is 50 Ohms, and you
don't have to worry about the fact that there is also 2800 PF of
capacitance. A receiver input generally has a transformer, or other device
that transforms the 50 Ohms to hundreds, or a few thousand Ohms. In
connecting a transmission line to a parallel tuned LC circuit, you don't
connect the line to the top of the LC. Rather you connect it to a tap near
the bottom of the inductor, or you add a second winding to the inductor to
make it into a transformer.

Tam/WB2TT

"mike" wrote in message
...
When researching the cost of high impedance coax as a feedline, it
apears globs of coax induced capacitance seriously degrates the
ability to tune the circuit. Under these conditions, resonating
frequencies requires extremely low inductance values.

How do people get around this problem in a receive only situation?

thanks,

mike