Previously a panorama was traced about the scientific and technological evolution of the Electronics in the military communication. However, considering this advanced technological context an interesting aspect is distinguished, not only for its simplicity, ingenuity, but, also, for its versatility that only the Radio as media could offer, in the case the FOX HOLE RADIO.
At the first glance, one could be thought it is related with a sophisticated device developed in the most secret laboratories of the Armed Forces. However, in the reality it is nothing more than a simple crystal receiver.
This type of radioset uses a piece of crystal - the galena or lead sulphide - as a radio waves detector.
As aforementioned in early chapters the crystal receiver detects the radio waves by the principle of rectification, discovered in 1903, by the American researcher Greenleaf Whittier Pickard.
In this way, the FOXHOLE RADIO is peculiar as in the place of a piece of galena crystal it used a simple razor blade. Yes, that's right, just a simple razor blade! Nowadays, replaced by the one-way razor pack.
Due to the structural characteristics of the steel used in the manufacture of the original razor blade, it could behave as a rectifier - i.e. allowing the passage of AC oscillations in just one direction - and so it was capable to detect the radio waves.
Basically, the FOXHOLE RADIO comprises a single razor blade, a small contact pin made of pencil lead actuating as the famous cat's whisker and a high impedance earphone.
In the battlefield the GIs of the allied armies looking for news about the war or even the far way home, invented this type of receiver using simple parts, as a razor blade. The most sophisticade one in the case of the earphone, it was taken from the radio communication equipments available.
In spite of its simplicity, through this kind of radioset Armed Forces radio stations up to twenty -five miles away could be heard, using a fairly good antenna and ground.
In case of interest, this fantastic receiver can be constructed easily using simple materials found everywhere else.
The most difficult part is the earphone. However, with a certain dose of patience, by looking in flea markets, junk yard or even at some aunt's Mary attics, one can get it from an old telephone. Old telephones use high impeadance earphones and so they are suitable for such purpose.
You should try it! It is just a fantastic experience for us accustomed to high-speed computers and the INTERNET one can feel the importance of this simple kind of radio for the soldiers far way home, anxious for news about the war and home. (a)

a) Schematic diagram of the fox-hole radio.

A - Antenna connection. This nail also fastens the coil form to the baseboard;
B- - Baseboard: 100 mm2 x 6 mm in thickness.
C - Coil form: comprising a wood block, 90 x 50 x 6 mm;
D - Area of the coils scraped clean along arc of switch arm;
G - Ground connection. This nail also fastens coil form to baseboard;
J - Jack for phones. Paper clips held down by tacks;
P - Detector. Pencil lead wrapped with copper wire and resting lightly on razor blade. Some adjustment of the location and pressure of the lead on the blade may be required;
R- Razor blade held down and connected to wire by tack;
S - Screw or nail for pivot of switch arm;
SA- Switch arm made from paper clip;
T - Thumb - or any kind of tack;
W - coil widing, approximately 175 turns, nº 26 insulated copperwire

This type of FOX HOLE RECEIVER, was very used for the soldiers of the Allied Armed Forces, during the Second World War, in the theater of operations of the Pacific, whose project was taken off of American magazine QST, edited in September of 1945.