JAMMING THE WIRELESS.

Hokitika Guardian, 9 February 1917, Page 4

JAMMING THE WIRELESS.

How a Raider Works. Tbs cables which describe tbe movements of the German raider now roving in the South Atlantic indicate that the Germans are playing the wireless game of “jamming” with great success. That prevents a ship’s message For assistance being picked ap, and at the same time makes it impossible for the Allies’ scouts to locate the position )f the raider. It is probable that the memy ship is fitted up with an exceptionally powerful outfit, one capable if “ jamming ” anything sent out from in ordinary merchant ship. Most traders carry sets of about one and a balf kilowatts, while the German on its present mission, would be fitted with one eqnal to at least ten kilowatts. The small apparatus ussd by the mercantile marine is quite poweriul Bnough for ordinary work, but when it oomes to an argnmont with 10 kilowatts it is a case of light-weight v. heavy-weight. As far as is known the raider is of about 700 tons, which means that she would carry rather low masts, which would be detrimental to the successful working of the apparatus over long distances* Though the operator would not be able to transmit direct to his headquarters, be could easily receive news of all home doings. Low though they be, tho aerials are high enough for the task which they are expected to perform, beoanee a raider always operates at close range. Having sighted a vessel the enemy would open ap communication at about five miles, and after disclosing his identity the wireless man would stand at the key and wait for the other operator to flash off the signal . ; . the recognised distress call, Before he would have time to give his own position or anything concerning him or the raider the enemy would commence “ jamming ” all messages sent out. That is done by simply transmitting on the same wave length as that used by the other station, In other words if on 9 installation is radiating ether waves on one wave length, all receiving stations adjusted to that wave leDgth will receive those

signals, which will interfere with those from another station seeding on the same wave length, aud so make the original signal unreadable, The signal most likely to be med for “j learning ”is made by keeping the key depressed forlOir 15 seconds- Another good interrupter is made by sending out . , . (‘‘V ”) at irregular intervals. It is easily seen that the operator who would be listening for a call would pick np, at the same time, both the S.O.S. and the jumble of letters from the raider, consequently he would be nnab'e to read either,

Tiffs’ trouble is tljwly being mastered, and with the modern receivers the operator is sometimes able to distinguish the s'gnals of one station, providing it has a pure musical note, of a pitch appreciably different from

that of the other stations. The advantage gained by these receiver.>, however, is lost if the interfere g station is neater to the receiving station than the other ship, because the “ jamming ” eignels will then be l rong enough to drown all other signals if they are of a different note.