It's always interesting to read about how the low VHF band above 30 MHz was used over the years for various applications. In the United States in the decades after World War 2, they used doppler shift on the low VHF band to find the location of rockets that had been launched.
The antenna above is a helical antenna operating at 36.9 MHz which sent a radio beam up towards the rocket after launch. A series of similar receiving systems would then pick up the reflected signal which would be shifted slightly in frequency due to the motion of the rocket i.e. the reflected signals would have some doppler shift.
By examining the data afterwards, the exact position of the rocket at any particular time could be calculated.
The antenna shown above is at the White Sands Missile Range Museum in New Mexico. If we examine it closely then we can see that it has three turns so we can estimate the gain to be roughly 8dBd, have a beamwidth of about 60 degrees and is of course using circular polarisation.
The plaque on display reads as follows...
"36.9 Megahertz Helix Antenna Doppler Velocity and Position (DOVAP)
Reference Transmitter Antenna
Developed during World War II by the Germans as part of a V-2 guidance and control system, DOVAP traced the course of a rocket using the Doppler Effect caused by a target moving relative to a ground transmitter and receiving stations.
Unlike radar, Dovap did not allow scientists to "see" the rocket on a screen. Instead, it sent up radio waves, which were received and rebroadcast back to earth by the rocket. The returned waves combined with the original ground broadcast and produced a musical tone which varied with the rocket's speed - the faster the rocket, the higher the pitch.
DOVAP data was extremely accurate: it could place a rocket's position at 100 miles up within 50 feet. It could collect data at the extreme altitudes of 100 to 300 miles. Dovap's disadvantage was that it took 3 to 4 weeks to reduce the data.
The antenna is a helix because of its physical and electronic characteristics. A helix is simple to construct and operate, provides necessary signal gain and directivity, and can be operated in several modes or polarizations.
The DOVAP system provided trajectory data and ground guidance for most of the early rocket systems: Corporal, Sergeant, Honest John, Little John, Redstone, and Aerobee Upper Atmosphere programs.
This particular antenna was built in the mid-1960s near C Station. Like much of the early instrumentation used here, it was designed and built at White Sands Missile Range.
Erected by White Sands Missile Range Museum. (Marker Number 06.099.)"
