"SCRAMBLED" SPEECH

Evening Post, Volume CX, Issue 122, 20 November 1930, Page 20

"SCRAMBLED" SPEECH

'/■■■. •■; .The telephone conversation held be-y-'^yeen Wellingtoii and London; on Tues■■''f.?day night, when Cabinet Ministers and -•others talked --with the Prime Minister -'"'and. his' party; has naturally aroused :i •'" ' great, deal of interest, as it is the fore?'runner.:of the inauguration of ;i com:i'niercial radio.telephone services between £'„ here.and the Old Country. The service "rj'has been\iti Operation for some months £.:.jfronr Australia. There appears to be

some difficulty about securing reliable speech transmission between Wellington and Sydney, from which the liighpower wave necessary to reach ..England is -sejit"-;tfuti""ii'u"f:"th'e" difficulties lia've been 'persistently attacked and should not be troublesome. Quite a number of owners of. short-wave receivers have listened to- the .telephony tests that have boon in. progress, and their ability to overhear, cdjiycrtsations is one of the drawbacks, of the: system. However, radio' telephony can. be made quite secret" by' Vir'syktcm of "jumbling"' whioh-is in reguliir use. This is one of tlic'.niost "-interesting features of radioplio'iie practice The principle is quite easily understood if one has any knowledge of wliat the- word "beat" means. It is.understood by most-wire-less: enthusiasts-that if one wireless wavei.-encounters aitother a "beat" or |"hot.erpd3'ne" note results.-This is the caus^-of •the- squeals and howls one heai's in J;'.Wcllingoon on Wednesday 'nightS.Precisely the'same thing happens whenithe.' waves -concerned are of the I much. ioVer -frequencies concerned with' ■ speech: Ordinary, spooeh contains useful frequencies ranging-from, say, 200 to 2000 o:yclps per.second. These can bu'made: to::"beat" ytrith an artificially, created-'frequency (say 2200 cycles) in such a."way ,that alow note of 200 cycles,produces- a beat note of 2000 cycles.'.andra high note of 2000 cycles prodwe'es a Ireat note- of 200 cycles, and instead of. the, original speech sounds, the .beat'notes, can be;transmitted. In thisUvay .liigh frequencies, such as arc involvf;d."iii-. the '.pronuaiciation oi' sibilants 'andf-cSrispiiaiits/'are transmitted, as lowViretos/.aiid low,. Vowel sounds go throtigh:;rtlie-. : asr as .high ■frequencies. It is. cjriite' inipossible -to -unfestand speech "soranißled"/-in ;t.his way. At the oflicialj receiving, station, lioweyer. tlie' ; distoTJ:'eiaj.Spceeh' ■ .is' again made to' "ljeat"','.Tritlt;tlib note usekl in reversing the'speech'frequencies, anil the original speech reappears:. . .. :'