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====== P-720 ======
**Miniature direction finder P-720**, **Telefunken PE 484/2**; manufactured by [[Telefunken, Berlin|Telefunken GmbH, Berlin / AEG - Telefunken, Ulm]].

The Telefunken PE-484 miniature direction finder was used as an "spy radio direction finder" by the Swiss army: the early version of the miniature direction finder PE-484/2 developed around 1958 was equipped with valves and transistors and the later version PE-484/5 with transistors only.

{{:images:p-720.jpg?direct&600|Miniature Direction Finder P-720}}
===== Technical data =====
  * Principle]]: [[single conversion superhet]], [[IF]] 470 kHz
  * [[Operation modes]]: [[A1|A1 (CW)]], [[A2]], [[A3|AM (A3)]], [[A3J|A3J (SSB) with BFO]]
  * [[Frequency range]]: 1.06 - 20.6 MHz
  * [[Sensitivity]]: [[A3|AM (A3)]] / [[Selectivity]]: 

==== Power supply ====
  * [[Batteries]]: two 1.2 V NiCd accumulators using a voltage converter to generate plate voltage, one 1.2 V battery for valve heating.

==== Dimensions ====
  * 1.12 kg

==== Accessories ====
  * **Directional antennas**
    * Ferrite antenna
    * Direction finding frame antenna with rod as an auxiliary antenna mounted on a tripod
    * Concealed frame DF antenna in fabric to be weared underneath the coat 
  * Signal strength meter in wristwatch design

----
{{:images:p-720-front.jpg?direct&600|Miniaturpeiler P-720}}
===== Operation =====
The miniature direction finder PE-484 developed in the late 1950s was used as an "spy radio direction finder" in the Swiss army. The earlier version PE-484/2 is equipped with two 5678 battery valves and transistors and the later version PE-484/5 with transistors only.

The direction finding receiver consists of a bakelite cabinet, ferrite coil cartridges are inserted to select the individual wavebands. The frequency dials mounted on the coil cartridges can be read through a viewing window. The operation modes are [[AM]] ([[A3]]) and [[CW]] ([[A1]]).

As antennas, the ferrite antenna can be used for high field strengths at close distance to a spy transmitter; as an alternative, an antenna sewn into a square fabric could be worn under the coat of the radio operator. All accessories could be stored in a briefcase.

For long-distance direction finding, operation on a direction finding tripod was also provided. The tripod, the associated direction finding rotary head, a large frame antenna and a rod antenna as an auxiliary antenna for side determination were stored in a innocious looking leather suitcase together with the direction finding receiver.

{{ :images:p-720-s-meter.jpg?direct&250|S-Meter - Wristwatch P-720}} A legendary accessory of this "spy radio direction finder" is the signal strength instrument, which is designed in the form of a wristwatch. The operator - if wearing the frame antenna under his coat - had to turn around his own axis while looking at the "wristwatch" to determine the direction of the bearing. The sound was then checked with an earphone.

The receiver is designed as a single conversion superhet: The RF signal from the antenna is mixed with the oscillator signal to generate the IF of 470 kHz. After three IF amplifier stages, the signal is demodulated and fed to a double stage AF amplifier. A [[BFO]] can be activated to receive [[CW]] transmissions.

The compact 1.12 kg weight direction finder receiver is powered by NiCad batteries of type 450D (2 x 1.2 V) (converter to generate plate voltage), another NiCad battery 900D for the tube heaters, the batteries are carried in a belt pouch.

===== Technical principle =====
Single conversion superhet, three IF amplifier stages, demodulation, then two AF amplifier stages.

==== Tube assembly ====

==== Development ====

==== Use ====
The Telefunken P-484/2 / P-720 miniature direction finder was used for agent direction finding and was liquidated in 1990.

{{gallery>:images?p-720*.jpg&0&80x80&lightbox&showtitle&titlesort}}

===== Technical documentation =====
  * {{ :manuals:p-720-pe-484-2.pdf |Small direction finder PE 484/2, Telefunken}}

==== Further information ====
  * [[http://armyradio.ch/radio-d/p-720.htm|P-720 at www.armyradio.ch]]
  * [[https://www.hamfu.ch/de/geraete/geraet.php?id=196|P-720 on the Hamfu website]]
  * [[https://www.radiomuseum.org/r/telefunken_peilempfaenger_pe_4842.html|P-720 on the website of www.radiomuseum.org]]
  * [[https://www.cryptomuseum.com/df/telefunken/pe484/index.htm|PE-484 on www.cryptomuseum.com]]