Amid the smell of blackpowder during the American Civil War, an idea took root in the mind of a German Army officer. As an observer of Union troops under General George McClellan, Ferdinand von Zeppelin was tasked with monitoring the tactics and outcomes of various manuevers in order to take back with him whatever knowledge might be of use to the German army.
At his disposal, McClellan had a number of “balloon camps” that provided aerial reconnaissance of battles in progress. Leading one of these camps was American scientist Thaddeus Lowe who had sold the idea of aerial recon in a personal demonstration to Abraham Lincoln in June 1861 when he ascended 500 feet above the White House and telegraphed back down to Lincoln:
“I have the pleasure of sending you this first dispatch ever telegraphed from an aerial station.”
In 1863, Zeppelin made his first ascent in a tethered observation balloon. He was 25 years old at the time and this singular event determined his life’s ambition from that point forward. Military campaigns and other duties in Germany would occupy Zeppelin’s time and career until 1891, during which time he repeatedly designed non-tethered balloon concepts on paper as he sought official support for his ideas.
Zeppelin made his first flight in a non-tethered airship – soon to be called a Zeppelin – in 1900. The flight lasted 20 minutes. In 1906, two more flights were made in an improved airship and, in 1908, another. The German military finally took notice and 6.5 million German marks were now available to move forward with this new technology which proceeded on both military and civilian fronts.
From 1908 to 1914, Zeppelins transported 37,250 people in 1600 flights without incident. Then World War 1 began.
Airplanes were in their infancy in 1914, as were internal combustion engines. They lacked both the carrying capacity and the range to lift heavy bombs and transport them to the enemy across the English Channel. Zeppelins to the rescue!
Flights from Germany to England could not make use of visual landmarks such as the roads and villages that allowed for domestic civilian flights. Furthermore, the altitudes at which the Zeppelins would be flying to evade enemy fire would have rendered such landmarks useless. Radio technology was new and poorly understood in 1914 but a system of radionavigation was developed that would allow consistently reliable trips across the English Channel and back again.
A system known as Telefunken Kompass Sender was in place from 1907 to 1918 and enabled Zeppelin navigation by a process known as “reverse RDF”.
Typically, regular RDF (radio direction finding) would make use of rotatable loop antennas on the moving vehicle, ie a ship. The navigator would turn the receiving loop and note its orientation as a null or peak in reception level occurred. Since the transmitting station’s location was known, a bearing to it could then be determined. The process was repeated with a bearing determined to another transmitting station – the intersection of these two bearing lines would be the ship’s location.
But for efficiency and accurate resolution at the low frequencies used, the receiving loops were too large to be practical on an airborne Zeppelin. Telefunken Kompass Sender’s reverse RDF process put the large loop antennas on the transmitting end. Now, instead of turning an antenna while listening for a null, the antennas transmitted the nulls as they rotated at a predetermined rate. All the navigator on the Zeppelin had to do was listen for the null. By knowing the landbased QTH (transmitted in Morse) of the station he was receiving, the rotational rate of a its loop antenna (printed on his chart) and the time delay between peaks and nulls received, a bearing line to that station could be derived.
The receiving antenna on the airship could be simple with this method – no need for a moveable loop. It came to be called an End-Fed Zepp and would eventually be used at ham stations around the world.
A bit more Zeppelin trivia:
It didn’t take long for Zeppelin navigators to notice that a wind-blown End-Fed Zepp made accurate fixes difficult. Newer designs used a peilgondel (a lead weight) to stabilize the dangling antenna. German engineering being what it is, the peilgondel soon morphed into a spahgondel - a gondola that could carry an observer while simultaneously serving to stabilize the antenna.
The observer could be lowered on a cable (the antenna) up to 1000 meters enabling him to see the ground while the Zeppelin remained hidden in a cloud bank. An intercom allowed him to communicate with the Mother ship as to when to drop the bombs. This was considered choice duty as it allowed the observer to light up a cigarette safely away from the Zeppelin’s hydrogen.