[TowerTalk] Radial Length

[Tom Rauch]

 >Is there a formula for determining the radial length, i.e.
other than 468/f
 >MHz ???   I am trying to get a High Sierra 1800 Pro to
resonate on my Motor
 >Home and have not been successful, as of this writing.

Having been through the mobile exercise several times, I
suspect you probably either have the antenna mounted against
the vertical sheetmetal, wiring, ladders, etc screwing up
the ability to radiate and making it more like a stub or you
have it grounded to sheetmetal in a way that has a poor
ground or a resonant ground.

My F-250 pickup trucks  very clearly showed resonances when
the bed was not bonded to the cab (the cab floats on rubber)
that greatly influenced SWR on some bands, even though the
mounting location was nearly ideal (the antenna was above
the upper rail of the bed, and the coil above and a few feet
behind the cab).

The thing that gives you a fairly low impedance ground is
the capacitance massive surface area of metal spread all
around. The walls, floors, tops and so on....not two skinny
sticks running the length of the bottom. When that metal
isn't bonded to whatever the antenna is grounded to with
short direct connections, it certainly can have resonances.

I'd look at the mounting and bonding of large pieces of
sheet metal first. I don't know how you will get an antenna
away from or above the sheetmetal in a big metal box, but
that's what you might have to do.

73 Tom