RF Systems
LFA520 Longwave
Active Antenna

Order #3060

Not Currently
Available

Many shortwave listeners have discovered that the longwave bands are not "dead". On the contrary, the longwave spectrum is filled with many interesting stations: sub-marine communications and other military stations, time and frequency calibration signals, positioning systems like LORAN, hundreds of NDB's (non- directional beacons), NAVTEX radioteletype, longwave AM broadcasting (Europe), the amateur bands, differential GPS (DGPS) stations, lowfers and the GWEN (Groundwave Emergency Network), weather data stations, and so on and on. Although most receivers have a frequency range starting at 30 kHz, often only stronger stations are heard. The reason is that longwave reception requires special antennas. Normal long or random wire antennas receive only stronger stations due to their limited height and impedance mis-matching.

Reception of radio waves with a frequency lower than 500 kHz is more complicated than shortwave reception. Thanks to the extremely long wavelengths (600 meters or more!) very large passive antennas are required. For vertical polarized signals very high antenna masts, and an ground systems are normally required. Horizontal wires must be several hundreds of yards long and have the disadvantage, that due to the limited height (less than 1/4 wavelength), the antenna "looks upwards" in the sky, with reduced sensitivity for the radio waves coming in at low angles from stations at longer distances. There is also an impedance matching problem. Even with longer wires, such an antenna is always short with respect to the wavelength (100 kHz is already a wavelength of 1.8 miles (3 km). Such an antenna has a high, capacitive impedance. The connection to the 50 or 600 Ohms antenna input of the receiver gives extra signal loss.

The RF Systems LFA 520 long wave antenna design was originally conceived to fill a professional application. This active antenna provides extremely high specifications in its operation range of 9 to 520 kHz. The E-field probe-amplifier inside the antenna as well as the filter inside the DC adapter reject strong medium and shortwave broadcast signals, in order to overcome the problem of receiver overload. The amplifier has extremely high intercept points, so intermodulation does not occur. The very low noise figure (much lower than the atmospheric noise) assures that even the weakest signals are received. The +10 dB gain over the whole frequency range assures, that even weak signals are amplified to such a high level, that they fall within the working range of the AGC of the receiver. This also overcomes the problem of reduced longwave sensitivity that many general coverage receivers have. The antenna has a height of 6.9 feet (2.1m). This is very small compared to the received wavelength. To improve the efficiency, the topload of the antenna is a 3/4 sphere with a diameter of 32 inches (0.8m), made of 4 radials. The antenna is weatherproof: it can operate from -22° to 150° F (-30° to +70° C), and can withstand wind speeds up to 100 mph (160 km/h) without damage

Specifications:
Frequency Range: 9 - 520 kHz ± 3 dB (down to 5 kHz at - 6 dB)
Rejection of Unwanted Frequencies: 520 kHz - 1 MHz: increasing from 3 to 50 dB, 1 - 108 MHz > 50 dB
System Gain: 9 - 520 kHz: + 10 dB
Polarization: Vertical
Reception Pattern: omni-directional
Noise Figure: 4 dB
Second Order Input Intercept Point: > + 70 dBm
Third Order Input Intercept Point: > + 40 dBm
Dimensions: 6.9 feet (2.1m)
Wind Load: 100 mph (160 km/h)
Maximum Length of Coax Between Antenna and Indoor Unit: 300 feet RG 58 or RG 213 (not included)
Output Impedance: PL259 plug, 50 Ohms (Output is short-circuit proof).
Power Required: 13.8 VDC