Longest practical ground cable?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Garry Freemyer by way of Terry Fritz <twftesla-at-uswest-dot-net>" <garry-at-ndfc-dot-com>

What's the longest RF ground cable I can have?

I've been thinking maybe I could drive a rod on the edge of my porch.
Trouble is, the thing is 30' away. That seems to be too long. With ham
radio, if I remember correctly, the ideal ground cable has to be shorter
than a quarter wave of the frequency you are transmitting on or it could act
as an antenna.

I'm assuming it's the same with TC's