Topband: K9AY Loop Revisited

[K9AY]

> I'm a little perplexed...Tom W8JI


Hi Tom,

Comments below...

> I formed my opinion because the model you sent me is extremely
> sensitive to the connection of a wire representing the shield of the
> cable to the antenna's ground.
>
> It was more sensitive to the "coax" shield connection than anything
> else I did...and the pattern distortion was huge!

I do not normally share the model I use for the K9AY loop, since
it knowingly violates some NEC-2 modeling rules in order to obtain
a reasonable correlation to observed behavior. I use it solely to
evaluate the radiation pattern of the loops. NEC-2 should not be
trusted to evaluate anything connected to, or lying on, ground.

> Even if we don't have such pattern distortion in real life, we have
> potential common mode noise.
>
> The bulk of urban and suburban noise problems are related to power
> lines and powerline operated devices, such as computers and other
> line operated devices. These devices have a direct connection from
> the offending source to the station ground via the power lines.

While common mode noise can be a significant issue in some cases
(e.g. Beverages, where their length supports efficient coupling), I think
it is overstated for most practical installations. At radio frequencies (as
compared to 50/60 Hz), radiated noise will almost always swamp out
common-mode (conducted) noise. Much of the energy in conducted
noise will be radiated before it reaches the station ground. Some
portion of the remaining current is induced onto the transmission line
shield via the shared ground (another lossy energy transfer). Then, with
that line lying on the ground or buried, much of the remaining energy is
dissipated into the lossy dielectric earth.

73, Gary
K9AY