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How Jap Radio lUnsmitters WorkIn 11. S. Hands

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.t tPescrSpfion of Japanese MSssdio Equipment Captured on t^uadaleanalJ I A ! ^ E S I I . S S I I T H . I t T I c , H S N I I

captured practically undamaged, having beenabandoned intact by the hastily retreating en¬emy forces.

The Btory of that action, minor though It was initself, unquestionably would make an interestingnarrative. This, however, is not an account ofmilitary operations; it is adescription of thosetwiptured transmitters and the way they were putt o w o r k i n t h e A l l i e d c a u s e .

First on the scene after the abandoned equip¬ment was spotted that August day was MasterTechnical Sergeant F. L. Ferranto of the II. S.Marine Corps. (You will remember Felix Fcr-ranto as one of the radio operators accompanyingAdmiral Byrd on the TT. S. Antarctic Expeditionof 1940.) Recognizing the value of the find, hewent to work on the rigs immediately to convertthem from tiieir heatiicn state into righteouaworkere for our cause. The author bad the privi¬lege of working with Sgt. Ferranto in convertingthese transmitters, and later participated in op¬erating the station over aconsiderable period oftime —in fact, throughout the hottest times onG u a d a l c a n a l

Three of the four transmitters were bigh-fre-

In th is war, cap tured enemy mater ie lpromptly stoes to work against its mak¬e r s - I n t h e S o u t h w e s t P a c i fi c , l a s t y e a r ,

f a s t a s t h e B f a r i n c a c h a s e d t l i c J a p so u t o f a p o s i t i o n t h e y p u t t o u s e t h esupplies left hehind —● intduding theradio e»iuipmcnt. One such radio instal¬lation, captured at aJap base in theSo lomons , was p ic tu red on page 17 o fQST fo r Apr i l , 1943. Here is the s to ryo f fou r cap tu red Japanese t ransmi t te rswhich performed asimilar service forthe U. 5. Forces fighting on Guadalcanalduring the autumn of 1942,

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THE month of August, 1942, marked thebeginning of the story of fotir Japanese radiotransmit ters which served as ameans of com¬munication for the U. S. forces on Guadalcanalover aperiod of several months.

These transmitters were part of an enemy radiostation found by apatrol of IT. S. Maiines in thewake of aJap retreat. The entire station was

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Schesaatic of the captured Japanese high-frequency Iran stni iters, as traced by the axithnr and \TSJW V. The circuitnhoivn indudcB the modifications for c-w, operation de&crihed in the text. Contrast the obsolete lubes with the

elaborate baud-awitcblng and control systems. Although Japanese made, the tubes were replicas of U. S. types.a n

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Captured Japanese transmitters used by the V. ̂Marines on Guadalcanal, and the men who operatedthem. Left to right —l,orcn Van Hoy, RT3c;IT. Smith, RTlc, and Leon V'oodard, RTle, W5JWV.

quency rigs having afrequency range of from3700 to 18,200 kc. The fourth was alow-frequencyjob with arange of from 50 to {>00 kc. The latterisn’t of particular interest here; it’s enough to saythat it consisted of a2-kw. vacuum-tube oscilla¬tor in aseif-excited Hartley circuit.

The three high-frequency transmitters >vere uUof the same type, as indicated in the accompany¬ing photograph. The circuits and tube line-up

shown in the schematic (on the oppositepage), traced oat wire by wire by the author andLeon Woodard, W5JWV.

This schematic shows the transmitters exactlythey were originally designed by the Japs, with

two exceptions. The-se exceptions are in the ̂ d-\>ias system for the final stage and in the provisionfor keying. The transmitters as used by the Japswere 'phone rigs employing grid modulation. Weput them on c.w., however, necessitating are¬design of the biasing aiTangement. This also re¬quired akeying relay, and the only one availablewas apolarized d.c. relay of Japanese make. Be-

of designing difficulties, this relay wasmade to control the plate current to the oscillatortube, it's the resulting circuit, as modified, thatappears in the diagram.

The circuits used in the transmitters were ofconventional, although somewhat out-dated, dersign. The layout stai'ted with aHartley oscillator,either crystal- or self-controlled. This oscillator,parallel-fed, was capacitively coupled to asereeii-grid buffer stage. Succeeding amplifiers used addi¬tional tetrodes of progressively higher power,ending up with an 861 in the final stage. Thetubes, although of Japanese make, were perfectreplicas of our own.

Band-sv/itcl̂ with tapped coils was em¬ployed in the interstage circuits to cover the 3.7to 18.2 Me. frequency range, while the antenna

upling circuit made use of avariable inductor.All variable condensers and inductoiu, inciden¬tally, were controlled by complicated dial meeh-finiRmfl containing just about every type of geardrive conceivable.

Many other oddities in constructional methodscame to light in these sets. The master bandswitch was amaze of shafts and univcirsal jointswliich controlled all stages simultaneously. Theband sivitch arranged circuits so that only one (hpcould be found on each plate milliammeter'as itscorresponding stage was brought to resonance,reducing the likelihood of mistuning.

The main power switcli was an exceptionallyelaborate multiple-contact enclosed type in which

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the liigh voltages were brought up in sequence oneach r.f. stage as it was tuned, "rhe meters wereall mounted on insulatom and had two glass faceswith atwo-inch air space between them. Thefilament rheostat was avery heavy-duty tappedresistor with aknife-type contactor. The mechan¬ical construction throughout was elaborate andrugged, contrasting strongly with the archaicelectrical design.

The power supplies for the transmitters (notshown in the photograph) were c.onvenrionalthree-phase rectifier systems, each unit incor¬porating three complete d.c. supplies. Power foroperating the transmitters was obtained from alarge Japanese diesel-powered generator whichsupplied the entire island. Emergency power wassupplied by aJap 4-cylinder gas-driven generator.

The vqltage regulator used on the transmitterpower supplies was amasterpiece. Briefly, it con¬sisted of atransformer built as amotor —afieldand an armature, «nth bucking coils. The anna-ture rotated through an arc of 180°, driven by athree-phase motor geared down to avery slowspeed. The stai-ting, stopping and direction ofrotation of this armature were controlled Dy amagnetic switch and relays. The magnetic switchconsisted of avane mounted between two elec-

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The terminal-board connection label pictured here i?«memento confieoated from aJap field radio set cap¬tured on Guadalcanal by aU. S. Army infantry comiau-nications unit. This label -waB received from Sfrt. D.Atkinson, WIMYH, who wrote: "Did not miss up onmy QSTi even during the months on Guadalcanal, andkept ray copy of the Handhoah right along with me, too.**

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45September 1943

ia proportion to the wavelength, or about 4to 1.As we said before, the acorn supcrregen had agreatdeal more selectivity than the receivers using,stajidard tubes with which we compared it, sothat comparing the superhet to one of the latterseta is agood deal like comparing an ordinarycommunications super to an old-time regenerativedetector. Further improvement in selectivitycould be secured by going to alower-frequencyi.f., the limit being set by the frequency at whichthe superregeherative action becomes poorer andthe point at which the selectivity becomes toogreat to accommodate the frequency modulationtypical of many of the modulated oscillators use