Valdemar Poulsen (23 November 1869 – 23 July 1942) was a Danish engineer who developed a magnetic wire recorder called the telegraphone in 1898.

He was the son of the Supreme Court judge[3] Jonas Nicolai Johannes Poulsen and Rebekka Magdalene (née Brandt).

None of these devices had electronic amplification, but the recorded signal was strong enough to be heard through a headset or transmitted on telephone wires.

[8] One enthusiastic reviewer, noting the 30 minute recording time and other features, predicted that "this instrument will mean almost as much to the business man and to the world at large as does the telephone itself".

[9] However, its complexity and the lack of a means to amplify its recordings greatly limited its adoption, and the invention was financially unsuccessful.

The most important modification was the introduction of an atmosphere containing hydrogen in a strong transverse magnetic field.

Music played in the Poulsen station in Berlin was received 215 miles (345 km) away at Copenhagen.

Recounting the superiority of vacuum-tube transmitters, in his 1950 autobiography de Forest wrote that he had been "totally unaware of the fact that in the little audion tube, which I was then using only as a radio detector, lay dormant the principle of oscillation which, had I but realized it, would have caused me to unceremoniously dump into the ash can all of the fine arc mechanisms which I had ever constructed, a procedure which a few years later actually took place all over the world!

[18] In 1907 he was awarded the Gold Medal of the Royal Danish Society for Science, and in 1909 an honorary Doctor of Philosophy degree from the University of Leipzig.