JAMMING THE WIRELESS

Dominion, Volume 10, Issue 2995, 5 February 1917, Page 6

JAMMING THE WIRELESS

4 HOW A .RAIDER WORKS. The cables which describe the movements of tho (jerrntm raider how roving in the South Atlantic indicate that tho Germans are playing the wireless game of "jamming" with great success. That prevents a ship's message for assistance 'being picked up, and at the same timo makes it impossible for tho Allies' soouts to locate the position of tlio raider. It is probable that the enemy ship is fitted up with an exceptionally powerful outfit, one capable of "jamming" anything sent out from ail ordinary merchant ship. Host traders carry sets of about one and a half kilowatts, nhile the German, on its present mission, would be fitted with one equal to at least 10 kilowatts. The small npparatus used by the mercantile marine is quite powerful enough for ordinary work, but when it comes to an argument with 10 kilowatts it is a case of light-weight v. heavyweight. As far as is known the raidor is of about 700 tons, which means that she would in all probability 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, he could easily receive news, of all home doings. Low though they may be, the aerials are high enough for tho task which they are expected to perform, because a raider always operates at close range. Having sighted a vessel the enemy would open up 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 ... — . . which is the recognised distress call. Before he would have time to (jive his own position or anything concerning him to the raider the enemy would commonco "jamming" aIL messages sent out. That is done by simply transmitting on tho same wave length as that used by the other station. Jn othir words, if one installation is radiating ether waves on one wave length, all receiving stations adjusted to that wave length will receive those signals, v;liich will interfere with those from another station sending on the same wave length, and so make the original signal ' mnreudablc. The signal most likely to be used for "jamming" is made by keeping the key depressed for 10 or 15 seconds. Another good in- 1 terruptci' is made by sending out . . . — ("\ r ") at irregular intervals. It is easily seen that tho operator who would be listening for a call woul'd pick up, at the same time, both the S.O.S. and the jumble of letters from tho raider, consequently lie would be unable to read either. This frouble is slowly being mastered, and with the modem receivers the operator is sometimes able to distinguish the signals of one station, providing it has a pure musical note, of a pitpli appreciably different from that of the other stations. The advantage gained by these receivers, however, is lost if the inTeffering station is nearer to the receiving station than the other shin, because the "jamming" signals will then be strong enough to drown all other signals if they are of a different note.