[Lowfer] 472-479 kHz

[JD]

As I have been saying in print, it appears the FCC is likely to promulgate 
rules early in the new year.  There is no reason for them not to do so. 
Even the power companies can't fuss too loudly about that allocation, so far 
as I can see.  But a 7 kHz slice that will appeal to a relatively few 
operators is probably not a high priority right now, especially with so much 
of the Commission staff occupied with preparations for selling off even more 
UHF spectrum.

Antenna efficiencies will be as much as 9 times better in this band, foot 
for foot of antenna, relative to 160 kHz.  Remember, radiation resistance of 
extremely short antennas increases in proportion to the _square_ of the 
fraction of a wavelength.  For a vertical monopole, the radiation resistance 
can be calculated to a high degree of accuracy.  With a bridge (even a 
carefully homebuilt one), the terminal resistance of the antenna can be 
measured at the operating frequency.  All of that latter resistance, minus 
the radiation resistance, is loss.  Thus, it is fairly simple to determine 
the efficiency of the antenna.  The power needed from the transmitter will 
be scaled up by that amount, and scaled back by the conversion factor 
between a monopole and EIRP.  I don't have hard numbers in front of me, but 
I'm sure there will be plenty of articles when the time comes.

The math is not much trickier for loops, but real-world variations might 
introduce enough uncertainties that I'd want to ensure my own compliance 
with actual field strength measurements, if possible.  (Strictly speaking, 
the same is true for verticals, but as a practical matter that's only a 
concern if someone is seeking to squeeze out every last microwatt without 
going over the limit.  The basic math for a vertical is good enough that any 
errors will be on the conservative side, field strength wise.)

John