01-02-2012, 10:04 PM
Agree. We were transmitting and receiving shortwave sky wave propagation of varying range. For LOS propagation, which for us was VHF and UHF frequencies, we used for the most part the antenna systems that were included with the radio. Sometimes, when it was practical, we constructed antennas that maximized both LOS sky and ground wave propagation. In arid environments, this was important, as the ground did not conduct well. For standard military VHF man packed radios, about 7 kilometers was the best you could rely on. Later, we had UHF radios that could reliably be used for 10 kilometers. There were times, when we were experimenting with these sets, when we communicated more than 20 kilometers, this was in mountainous terrain with both stations significantly elevated. If you had an aerial relay platform in support of your operation, your VHF and UHF range was dramatically increased. Usually these were MH-53s, MC-130s or AC-130s.
For shortwave comm we almost always constructed our own antenna systems. For relatively close (10 to ~300 miles) communication we used what is called NVIS (near vertical incident sky wave) antennas. They tended to be omnidirectional but were effective. This was especially good when communicating with a ship that was loitering 100 or so miles off shore, as the omnidirectional radiating property of our antenna went well for a ship that was constantly moving in a preplanned area.
For longer range comm I preferred either a sloping wire or a sloping V antenna, as it was fairly simple to determine the orientation and takeoff angle, and was easy to directionalize. I was able to transmit reports from the carribean and south/central america with a 20 watt radio using these systems. I did not like using a dipole because the lobes radiating from the antenna and the takeoff angle were difficult to control, as they were determined to a large part by the height of the dipole from the ground. In a clandestine situation constructing a "high" antenna was not practical.
Later in my career we received satellite communications sets (SATCOM) that made all the difference. They were smaller, lighter, had superior range and crystal clear sound quality. It was also at this time that we received digital equipment that allowed us to transmit reports and photographs in a digitalized "burst" transmission. The "burst" took less than a second, which reduced transmitting time and therefore prevented opportunities for the "bad guys" to direction find our station.
The circular waves you speak of may be the "lobes" that are radiated from all antennas. The shape, direction, and coverage of the "lobes" depend on the specific antenna. Although the lobes are "circular" in a 3-dimensional sense, the waves present in them are not.
For shortwave comm we almost always constructed our own antenna systems. For relatively close (10 to ~300 miles) communication we used what is called NVIS (near vertical incident sky wave) antennas. They tended to be omnidirectional but were effective. This was especially good when communicating with a ship that was loitering 100 or so miles off shore, as the omnidirectional radiating property of our antenna went well for a ship that was constantly moving in a preplanned area.
For longer range comm I preferred either a sloping wire or a sloping V antenna, as it was fairly simple to determine the orientation and takeoff angle, and was easy to directionalize. I was able to transmit reports from the carribean and south/central america with a 20 watt radio using these systems. I did not like using a dipole because the lobes radiating from the antenna and the takeoff angle were difficult to control, as they were determined to a large part by the height of the dipole from the ground. In a clandestine situation constructing a "high" antenna was not practical.
Later in my career we received satellite communications sets (SATCOM) that made all the difference. They were smaller, lighter, had superior range and crystal clear sound quality. It was also at this time that we received digital equipment that allowed us to transmit reports and photographs in a digitalized "burst" transmission. The "burst" took less than a second, which reduced transmitting time and therefore prevented opportunities for the "bad guys" to direction find our station.
The circular waves you speak of may be the "lobes" that are radiated from all antennas. The shape, direction, and coverage of the "lobes" depend on the specific antenna. Although the lobes are "circular" in a 3-dimensional sense, the waves present in them are not.
