MFJ MFJ-1784, Instruction Manual

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MFJ-1784 Giant Box Fan Portable Loop Antenna Instruction & Technical Manual
wave transmitted by a 2-meter VHF station has a frequency of about 145 MHz. Dividing the speed
of light (
∼ 3 × 10
8
m/s) by the frequency in Hz, we find that the wavelength in atmosphere of the
signal from our station is 2.06 m. Since wavelength and frequency are reciprocal, an increase in
wavelength corresponds to a decrease in frequency, hence, the 160 m band has a much lower
frequency of 1.8 MHz.
The electromagnetic spectrum (Figure 2) includes all of the various energies of electromagnetic
radiation ranging from extremely low frequency (ELF) ranges (with very long wavelengths) to all
the way up to x rays and
γ rays, which have very high frequencies and correspondingly short
wavelengths. In between these extremes lie radio waves, microwaves, infrared radiation, visible
light, ultraviolet radiation, and the entirety of the FCC spectrum allocation chart. The RF part of
the electromagnetic spectrum is generally defined as that part of the spectrum from about 3 kHz
to 300 GHz.
Figure 2: The Electromagnetic Spectrum
2 THE MFJ-1784
2.1 INTRODUCTION
The MFJ-1784 Giant Box Fan Portable Loop Antenna
™
is the next step in box fan antennas.
Adding four feet to the circumferance and fine tuning the physical dimensions for the perfect
inductance has created an antenna that functions on more bands than its predecessor while still
being slim enough to fit just about anywhere. Covering from 7 MHz to 22 MHz, this is the
best-performing portable antenna available to amateurs today with the same form factor as a 3
× 3
foot box fan. It has a convenient carrying handle and features remote tuning control. All tuning
and control voltages are coupled to the antenna through the coaxial feedline for a simple, neat,
single-cable installation. You can take it with you anywhere: a hotel, camp site, or any other
location. You can place the antenna on a picnic table, wooden table or any other non-metallic
convenient place, and you are ready to start operating. The MFJ-1784 requires no tuner and is self
tuned across all of its rated bands with an SWR less than 1.5. The driven element is constructed
from rugged aluminum sheeting. Every current-carrying joint is welded to eliminate
high-impedance pressure contacts that reduce efficiency. Finally, the MFJ-1784 is matched by a
superb, welded, low-resistance, high-current, butterfly tuning capacitor.
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