[Lowfer] Frequency usage question

[JD]

>>> And for Part 15, the vertical is more defensible for regulatory purposes 
>>> than a 50x50 foot loop.

Not a trivial concern, IMHO.  Equating a 200 foot run of radiating conductor 
to the total length of 15m specified in the Rules is quite a mental 
challenge.  (Conversely, for Part 5 Experimental Service licensees or hams 
in countries with LF allocations, it's no issue at all.  Licensed operation 
might be a better alternative than Part 15 for anyone stuck needing to use a 
loop because of local arboreal circumstances, anyway.)

Along with that concern, plus the lower radiated field strength for a given 
physical size as John A mentioned, the third disadvantage of a transmit loop 
is that it is directional.  The very property that generally gives loops a 
big advantage for receiving can be a detriment when transmitting.  Prime 
example:  On 2200m, I can generally see MP day and night because my QTH lies 
roughly in the same alignment as Mitch's loop; whereas MP is a 
nighttime-only catch for other folks who are at comparable distances or even 
nearer, but who are located off to the sides of the main lobes.

There are ways to fill the nulls of a loop, of course, but either at the 
cost of efficiency (ie, intentional or accidental coupling to other 
conductors--or even semiconductive natural objects--in the vicinity) or else 
by implementing a second entire loop and feeding it in phase-quadrature, 
which is even less realistic for Part 15.

John D