By definition, at least one end of a "ground lead" must connect to ground. Unfortunately a true r-f ground does not exist at the top of a long conductor connected to one or more buried conductors at its base, and attached at its top to the short "ground lead" of an elevated Part 15 AM transmitter + ~3-m whip.
Below is a chart showing how for other things equal, the groundwave field intensity of a Part 15 AM setup at 1 mile varies with the length of vertical conductor used between the end of the ground lead, and a buried ground rod.
The conductor lengths were chosen to cover the range of systems from one fully compliant with FCC §15.219(b) to those where the transmitter and whip are elevated up to 10 meters (32.8 feet) above the earth. A standard 8-foot long ground rod was used. The length of the whip antenna was 102 inches. Earth conductivity was set to "average."
The transmitter power was set to that possible from a transmitter having a Class E final amplifier capable of driving this load resistance with 90% d-c input to r-f output efficiency when adjusted to meet FCC §15.219(a).
The fields shown in the chart can be modified for other output powers by multiplying them by the SQRT(Other Power/90).
The field improvement at 1 mile for the system shown in the chart at 10-meter elevation is better than 5:1 compared to the system using only a 0.4-meter conductor length to the ground rod.
The system at zero elevation would need more than 25 times that 90 mW transmitter power to produce the same ~ 170 µV/m field at 1 mile as the system elevated 10 meters.
Also note that the system compliant with FCC §15.219 produces a higher groundwave field at one mile than is permitted at 30 meters for this frequency by §15.209.
I know I've posted such information in the past, but new questions continue to appear, so I keep responding to them -- hopefully in a way that better explains this subject.
The length of the ground lead depends
on where ground STARTS.
Best thing I've ever heard.
Bruce
You have a good memory that FCC agent comment.
My BC engineer friend is a reliable
source (then and always) and I believe
that the accuracy of the statement is
very high, maybe 100 percent.
What the agent said was (what we THINK anyway) is,
"If everything fits into
a 10 foot box I have no problem " -
as reported by my very good BC engineer friend.
That's all we know.
It was a long time ago. We don't know
who said it, and I'm sure whoever it was meant
3 meters, not 10 feet.
That's why I have experimented with big top hats
and thick antenna poles.
My equipment sat on the ground in the middle of the
back yard, so the ground lead was very small.
I decided back then that the ground was the center
of my 16 radial system, and everything was tied to that.
I still stand by my opinion, but it's still just
my opinion. If an FCC agent came by,
I would cooperate fully if it came to that.
If the station equipent got taken, well - the house has
too much stuff in it anyway. I am too old to get upset
about something like that.
It would never get to that point though, because
if an NUUO came in the mail, I would correct the trouble
or shut down or whatever. I LOVE Part 15 AM. But that's what
I would do. I'm too old to care, and I have done just about
every "radio thing" I've wanted to do.
In my imagination, I can see a 3 meter square
metal box out in the yard, on top of my AMT-3000.
For some reason, I don't think it would work very well.
If you got this far, thanks for reading my point of view.
You guys are the best.
Bruce
I love all of the engineering info that
you guys have posted about this.
VERY interesting and fun to read.
Bruce
My ground lead is 2.5-inches