Topband: Mixed RF grounds

[Dennis OConnor]

Yeah, it's counter intuitive but so is magnetism, quantum mechanics, and singularities (that's all the big words I know)The issue is that you are thinking of car batteries and your house electrical system where a single ground point is the best way to return currents back to the power source. 
    Now, in a way RF currents are similar to the electrical power company and in many ways not. Similar in that the ground currents induced into the dirt by the aerial up above need to be returned to the power source (the antenna) for it to work with any kind of efficiency.  It's the difference between getting a drink by just scooping your drinking cup into a pond versus trying to scrape a thin layer of water off the surface of a parking lot. The first way is far quicker but RF does not work that way. It is the second way for RF.
    Dissimilar in that just sticking a metal probe into the dirt returns only a minuscule portion of the induced ground currents. The currents are spread way out on the ground surface as they ripple along. So to return them efficiently to the antenna terminals you need a big capacitor plate laying on the surface to suck up RF current from a much wider area than just the cross section of a metal stake pounded in. 
    A sheet of copper coating the entire ground out to a few wavelengths would be the ideal return - but not highly practical. So we settle for radial wires which emulate a capacitor plate. Because the RF rippling across the radial wires induces current in them (see Maxwell) having bare metal touch the dirt is of no help for this job (and can be a hindrance in some conditions such as induced 60 cycle hum from the house wiring etc. 50 cycle in your case and bloody inefficient, that)    Now, for a few radials, short is better than long (another counter intuitive deal) Another way to say it is, for just a few few radials anything beyond 1/10th to 1/15th lambda is probably wasted.  Improvement would be a half dozen short radials compared to one or two two long radials.Leave the long radials you have and look for creative ways to add short ones in between them.
Another trick would be elevated radials ( above hand reach because they bite) Moxon recommends at least 4 of them as high as practical, approx 1/12th lambda, and loaded to resonance.    Oh, I'm full of it (ideas I mean :) as long as you are doing the work, eh wot.cheers

denny / k8do