Below ten meters, the manual of ultra-short-wave-radio

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Below

TEN METERS The Manual of

ULTRA-SHORT-WAVE-RADIO Compiled and Edited by JAMES MILLEN and ROBERT S. KRUSE

•

CONTENTS

• PAGE

Chapter 1-How Ultra-Short Waves Differ from Ordinary Short Wave s . . . . . . . . . . . . . . . . . . . . . . . . . .

5

Chapter 2-Generating the Ultra-Short Waves.... . . . . . . . . . . . . . .

11

Chapter 3 -Radiating the Ultra-Short Waves. . . . . . . . . . . . . . . . . . . . 20 . Chapter 4- The Ultra-Short Wave at Work . ............ . ... ... 25 Chapter 5-Experiments and Theories .. ... . .... ... . ........... . 29 Chapter 6-Measurements . ... ... . ... . ........... . . . . . ... . . .. . 36 Chapter 7 -Amateur Radio Communication Below 10 Meters ..... . 39 Chapter 8-Receiving in the Ultra-Short Wave Bands . . . . . . . . . . . . 50 Chapter 9-Receiving Television Signals at Ultra-Short Waves .... 58 Reference List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 History of Ultra-Short-Wave Development ...... . ........ . .. . ... 64

COPYRIGHT

1932

BY

THE

NATIONAL

COMPANY ,

MALDEN,

MASSACHUSETTS

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THE MANUAL OF ULTRA SHORT WA VE RADIO

*9*

is in its better ab ili ty to operat e on small obj ects. So much for our hurried outline, let us now move on to the ac tu a l generation of these ul tra-short waves. Startin g from th e top of page 9 we find, as one wo uld expect, t hat the regenerative , ·acuum t ube oscillator can be used, t hough its form is specia lized a nd it is not very usefu l below abo ut 1.5 meters wavelength. By ha rm onic amp lification one may proceed down abo ut two octaves furt her, a fte r which t he ordinary circui ts - even wit h refinements - cease working. Th is is detailed in Chapters 2 and 7. Below t his we encounter new a nd curious genera to rs in which electrons, fil aments a nd plates are used inside a vacuum tub e, but th e nature of t he oscillations is a new one altogether. On pages 16, 17 an d 18 th e ge neration of such oscill ations is discussed , their transmission for com munication pur poses is detailed in Chapter 4 and also page 47 of Chapter 7, a nd fi na ll y t heir reception is described in Chapter 8, page 51. So fa r t he receiver has in a ll cases been eit her a co py or a miniature of the t ra nsmi tter, exce pt in the case of measurements (See Chapte r 6) where it at times becomes co nve nient to use an ordin ary t un ed- circui t wavemeter or to ca use stand ing waves to appear on Lecher's parallel-wire arra nge ment as describ ed briefl y in Chapter 6. At abo ut 2 centimeters wavelength t hese ge nerators - a nd with them the correspondin g recei,·ers - stop wor ki ng. For a time we a re referred to the primi t i,·e spark-gap system of shocki ng metallic particles in to oscillation, exactly after t he mann er of Hertz a nd 18861 ! T he receivin g, meas urin g or detectin g a ppa rat us in this ra nge is ve ry poorl y developed as yet. Ju st below that even the spark ge nerators fa il a nd we mu st rely on t he ha rm onics of such genera to rs - an d minute powers - b ut we a re now beginning to emerge again in to the known a nd fa mi lia r, fo r t hese harm onics a re H EAT waves- and e\·en a child can detect heat witho ut special eq ui pment.

The right leg of this frog has been paralyzed by applying short waves to the left side of the spinal column . See chapter 4

A contrast in antennas at Riverhead, L. I. In the distance a line of towers stalks across country bearing a longwave antenna. In the foreground are two towers for medium and shortwave antennas, while on the nearest tower are two dark squares on each of which is an ultrashortwave antenna ARRAY of many small antennas, working at 65 cm. See chapter 4

Certain lamps ge nerate heat, light, a nd ultrav iolet light , so the overlap is complete a nd we ha,·e crossed th e ultrashor t wave region in t his series of rapid jumps. Now we shall take the rest of t his book to go back, to fi ll in detail , a nd to attemp t to be of practical use to the newcomer in t his fascinating region.

For additional · information on this subject, see reference list on .. page 63 ·

* 10 *

THE MANUAL OF ULTRA SHORT WA VE RADIO

CHAPTER 2 • • •

Generatin·g the Ultra-Short Waves Madam Glagowela-Arkadiewa and the spark oscillator used by her to generate the shortest radio waves ever produced, ranging well into the heat region. In this apparatus sparks were passed through very small metal particles which were constantly agitated to prevent burning. In this way the metall ic particles were caused to oscillate exactly as were the metal rods in the original Hertz oscillator sketched below, but the small size of the particles resulted in the very short wavelengths listed in the table below

O

U R ordinary long, medium and short-wave radio oscillators or generators are a lmost a ll of the type employing regenerative vacuum t ubes, either triode or tetrode. I n the ordinary shortwaYe region the regenerative triode is nearl y uni\·ersal but "below 10 meters" new means appear, familiar circuits fa il a nd e\·en the best of the regenerators do not go far below 1 meter.

of which examples a re pictured on page 11 ) a nd fina ll y two new varieties which are here referred to as "Magnetron oscillators" and "Barkhausen-Kurz oscillators." The last two are different from our ordinary oscillators in that they t rap electron s between filament and plate and cause them to swing back an d forth in that space for some t ime as will be explain ed in a moment.

Spark Oscillators Spark oscillato rs a re so fami lia r a nd so relativel y simple that they need not be described except by t he photographs and sketches herewith.

Regenerative Oscillators HERTZ

The regenerative oscillators used at ult ra-shor t waves a re without exception

close relatives. of the standard circuits but this does not mean that a ll circuits workin g well at standa rd waves will wo rk equall y well at ul t ra-short waves; on ly those circuits a re altogether satisfactory in which the t ube capacities do not interfere too seriously when t he external tu ning capacity has been reduced to a few micrornicrofa rads as is necessary when working at wavelengths much below 10 meters.

The Ultraudion One of the simplest a nd most dependable circuits is t hat shown at A, particularly if the plate supply feed choke and the grid leak (or grid bias) choke a re connected at the two sides of t he tuning condenser C rather than at t he points shown in the diagram. The circuit then becomes the same as dia gram G with the difference that there is no radio freq uency path from the tuned circuit to the filamen t. This is one of the old est of all oscillatory tube circuits. It is probably due to Logwood though

WENSTROM'S TABLE OF PROGRESS IN ULTRA-SHORT-WAVE GENERATORS Regenerative Oscillators

In a " Historical Re\·iew of UltraShort-\i\Tave Progress" appearing in the J an ua ry, 1932, issue of the Proceedings of the Institute of Radio Engineers, Lt. William H. Wenstrom has excellently summed up that subj ect to the close of 1931. The accompanying historical table is from t hat article. It will be seen that the ultra shortwave oscillators fall into four classes, the regenerative oscillators, which a re variations of the ordinary types, the spark oscillato rs (with wh ich radio began and

Wave Length (cm.)

Name

Name

Year

White

1916

600

Barkhausen and Kurz

Gutton-Touly

1919

200-400

van der Po l Southworth Holborn Mesny Gutton-Pierret

1919 1920 1921 1924 1925

375 110-260 300 100-500 50-200

Gill and Morrell Scheibe Grechowa Hollmann Uda

Phelps-Kruse Englund Yagi

1927 1927 1928

41-500 100-500 60-200

Bergmann

1928

80

Riti

1928

300

1930 1930

300 200

:.

Esau and Hahnemann Brown

THE MANUAL OF ULTRA SHORT WA VE RADIO

Magnetron Oscillators

Barkhausen-Kurz Oscillators

Beavais

Year

Wave Length (cm .)

Name

Year

Wave Length (cm.)

1920

43-200

Breit

1924

60-150

1922 1924 1926 1929 1930 1930

200-500 30-330 18 20-140 50 1 5-18

Yagi

1928 1929 1929 1930

15-100 30-65 5-40 3-15

Forro

Oka be Oka be

Spark Oscillators All wavelengths are listed in cm. and represent either the range investigated or the shortest wave·

length reached

Hert• Righ i Nichols and Tear GlagowelaArkadiewa

1887 1894

50 2-12.5

1923

0.18-0.4

1924

.008-0.S

*

11

*

Family of Ultraudion oscillators due to Phelps-Kruse. From right to left they work at 2.36 meters, 1.41 to .97 meters (depending on condenser), .87 meter, .63 meter and .41 meter, the last being the shortest wave which had been reached with a regenerative oscillator. The output in this case was negligible, the other tubes gave useful outputs of 20 to 50 % normal rating . All had tungsten filaments

Ultraudion transmitters. Above, demonstration type of Dr. Phillips Thomas, working at 240 cm. The tuned circuit can be seen hanging from the plate and grid leads of the tube. The feed chokes are at the right. Below, Joseph Noden 's 1 meter ultraudion of 5 watt size, showing tuning condenser (two discs) under tube, and the 2-turn coil partly on each side of tube. Feed chokes below

3-meter oscillator which may also be interpreted as an ultraudion and which is here mentioned for two reasons. The first is t hat it nicely ill ustrates the d ifficulty of na ming a circuit when the external t uning capacity has disappeared and the inductances are reduced to mere rods. The other is to poin t out one of t he simpl est of all amplifier systems for ul tra-short-wave transmitters. This

scheme works invariably and should be used more. At D is a variant of A which is more curious than useful. Th e circui ts B a nd E are not highly recommended below 10 meters. The circuit C is a lm ost as effi cient as the single sided ultra udion a nd if well balanced requires no radio frequency chokes which are a lways tro ublesome at ultra-short waves. Circuit F combines ma ny virtues if it is

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for some unaccountable reason it has lately been attribu ted to- Gutton-Touly at a t ime certainly ten years after its use by Logwood and DeForest, who called it "ultraudion." An ultraudion oscillator appears on the cover of this book and we see no reason for avoiding the na me in the text. Nearl y every long distance transmission listed on page 64 a nd in chapter 5 is due to this circuit, ca refu lly used. In the January, 1931 , P roceedings of the Insti tute of Radio E ngineers, Lieutena nt W . H. Wenstrom gives experimen ta! evidence as to the efficiency of t his a nd other circui ts. At H is shown a

*

12

*

Regenerative oscillators as used at 3 and 5 meters. Constants, where given, are fo r "7% watt" tubes. Circuit A is the "Ultraudion," used in many of the transmitters shown hereafter and working readily down to 1f2 meter. "Below 10 meters" it is advisable to connect the grid and plate r.f. chokes of this circuit to the two sides of the feed and tuning condenser C rather than directly to plate and grid as shown . All of these circuits are sometimes worked without any grid leak or other source of bias, but the efficiency and stability are much decreased

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THE MANUAL OF ULTRA SHORT WA VE RADIO

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75 watt 5 meter osci llator using the Colpitts-Hoffman balanced circuit of diagram F, 1 p. 12. Upper diagram gives dimensions, while the center diagram clarifies the balanced-bridge condition which makes feedchokes unnecessary. C1 and Ci are double-spaced receiving cond e nsers , final capacity .000125, originally .0005 . C3 is a fi xed air condenser, seen at the top of the transmitter and made of 6 sheets of metal, 5" x 7", laid up a s shown in bottom sketch, using spaci ng according to plate voltage X " air gap for 2500 volts. The resi stors in the main diagram provide thumpless keying

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carefull y made symmetrical. Dimensions for a 5-meter, 75-watt transmitter of this sort are indicated in accompanying illustrations. The obvious weakness of any regenerative oscillator in the ultra-short wave region is t hat changes in voltage or load

will have much more effect in changing the wavelength (or freq uency) of oscillation, as the tube capacities tend to take control when other capacit ies a re cut down. It is t herefore much more important to avoid chan ges of t hese tube constants as far as possible, which in general means that t he tube should oscillate without interruption of any sort when frequen cy-stability is of a ny importa nce as in comm unication. Oscillato r-amplifier transmit ters are relatively more desirable tha n at longer wavelengths, and a re shown in the chapter on transmission - chapter 7. Surely it is not necessary to stress again the supreme im por tance of constant

monitoring to make sure that one has satisfactory shielding, rigidity, filterin g a nd voltage regulation.

Crystal Control The methods of quartz-crystal contro l are now so well known that no repetition is needed here. In working down from a n 80- or 160-meter oscillator to a final output " below 10 meters " it is economical to use high-mu tubes such as '24 or '47 types (or even t he '41) unt il one reaches the v icinity of 20 meters, below which the pentodes and tetrodes are not very good, unless one uses the new '57 type, but they are rat her small. Triplin g, t hough good in the laborato ry,

Push-pull oscillators of the semi-Armstrong type with tuned plate circuits a nd sem i-tuned grid circuits. The diagram is correct for both. For '52 or H tubes For '10 tubes Li 1 turn , 3" diameter. 1 turn 4 " diameter. L2 11 turns No. 14, wound 1 " dia. 4 turn s No·. 14, 1 " dia. coil about spaced about ~ '·' . 2" long. C. National isolantite insulated type National type EMP, see p. 61 . TMP, a s shown below . R1 100-watt non-inductive . 20,000 25 watt non-ind. 10,000 ohms. ohms or more. RFC for both types, 18 turns No. 24 spaced ),{ 6 " on ~ " dowel.

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THE MANUAL OF ULTRA SHORT WA VE RADIO

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has not always been satisfactory, a nd a series of dou biers is still preferable. T he sore spot is t he necessity of starting so far away from t he desired wavelength. This can be avoided by t he use of a tourmalin e crystal-plate instead of a quartz plate. The wo rk on tourmaline oscillators has been done in Germany and our experience is still li mit.ed . Recent issues of QST have carri ed info rmation enough for a good beginning. T he res ul ts seem encouraging and may remove one of t he wo rst difficu lt ies in t he ul tra-h igh region. Doubli ng is still in order, of course. I t is perfectly practical to do uble a 5-meter oscillator 3 times

The tourmaline disc is cut from the original crystal as indicated by the upper sketch which shows the usual axes. The oscillating circuit is the normal one shown in the diagram. By dusting lycopodium or similar fine powder on the end of the oscillating cylinder irregularities are exposed by "patterning" of this powder as seen in the photograph. When the disc is truly circular and the sides flat these patterns tend to become concentric rings. The general procedure is as in quartz-crystal grinding. The efficiency gradually falls off as the d isc is made thinner as shown in the curve and one cannot go far below 5 meters

2

with qu ite ordinary tubes, a rnvrng at 62Yz cm . wit h good frequency stabil ity. Th us if one cou ld operate a crystalcontrolled oscillato r in the 5-meter or 6-meter region good frequency stabili ty wou ld at once become availab le over the upper part of the ultra -short wave region - 62 cm. to 10 meters. This is possible when using a to urmaline crystal plate instead of a q uartz plate. T he to urmaline plate is onl y about 131' t imes as t hick as qua rtz wo uld be fo r t he same wavelength, but it shatters less read il y

Push-pull Armstrong circuit (tuned plate and tuned grid) regenerative oscillator working down to 1.4 meters. Tuning is done with the sliders. With proper tubes this construction need only have the voltages changed to operate as a pushpull electronic oscillator of either "B-K" or "G-M" type (J . J. Lamb)

*

14

*

A simple construction used in. a German ultra-short wave oscillator. The mechanical arrangement, slightly modified, permits easy changes of circuit and wavelength. When desired inductances with stopping condensers may be plugged in. See page 27

than quartz and will work acceptably at 5 meters, whereas quartz can seldom be induced to hang together when ground thin eno ugh for 20 meter work. Thus in gene ral the same ultra-short wave can be reached with two stages less of doub ler than wo ul d be needed for quartz . Because of the extreme t hi nness of t he to urma li ne disc t he plate voltage must be modest - preferably not over 200, bu t when using amp li fier t ubes wit h a high mu, such as the 112A, 240 and 841 it is still possible to raise the power level while passing a long the doubler system. The fina l am plifier had best be a "straight through" a mplifier if fu ll output is a consideration . Barkhausen-Kurz and Other Electronic Oscillators Below about 40 cm . t he outp ut of a rege nerative oscillator becomes very

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THE MANUAL OF ULTRA SHORT WAVE RADIO

GRID

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li ttle regard for th e tuned circui t (Lec her wire system) con nected to it. This is t he ty pe of oscillation first described by Barkh a usen a nd Kurz, a nd named for them. In cidentall y, t he na me Kurz is prono un ced as if spelled Koor tz - just as t he long-abused pioneer of radio shou ld be called " Hair tz" a nd not " Hurts." However, electron-oscillato rs are NOT always independent of the t uned system. If eit her t he tunin g or th e vo ltages be changed grad ua ll y the a rra ngemen t wi ll pass t hro ugh conditions where the freque ncy is fa irl y well contro lled by th e tu ned circuit, though the type of oscillation remains about the same. In t his second cond ition we call th e device a Gill -M orre! oscillato r after t he first observers. In a recent Proceedings of ihe I nstitute of Radio Engineers, H ollman has shown how t he t ube jumps from one condi tion to t he other, a nd the most informative of his curves a re give n herewith. \•Vhether the ju mps take place at t he same wavelengt hs as in H ollma n's setup depen d s on a great man y things, especia ll y t he t ube design a nd vo ltages. Us uall y t he jumps "are whe re yo u find t hem " and one must by trial avoid a bord er-lin e co nd ition where a flutter ta kes place li ke t hat of a crys ta lcon trolled oscillator trying to work at two crysta l fr equencies at once. No matte r which of t he two schemes is used, extreme care as to voltage stability is v ital, a nd · t he output is very small, a nd at very low effi ciency. Most of t he power-loss is in the grid , whose small heat-d issipating ability li mits the whole affair .

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Mechanism of the Barkhausen-Kurz and Gill-Morrel oscillators. The highly positive grid starts the electrons out al high speed. Some strike it and give up their energy as heat; others charge through the openings in the grid, but are turned back by the negative plate, thereafter gyrating as suggested by the dotted arrow. These gyrations produce voltage changes in grid and plate which are transmitted to the leading wires. See text for frequency control and table for frequency limits small and one mu st reso rt to t he socall ed "electronic" oscillators. In t hese we operate differently from th e ordinary rege nerative oscillato r in wh ich t he grid is a so rt of fl utterin g valve modula t ing the plate-C urrent in to r.f. variations . Instead the action is as shown in one of t he drawings herewit h.

Gill-Morrel or Barkhausen-Kurz I t will be seen t hat th e plate is N EGATIVE a nd t he grid POSITIVE , exactly t he reverse of t he regenerative a rrangement. T ests have shown t hat sometimes t he frequ ency of t he oscillations depend s on th e voltages a pplied to t he tube, wit h

Simple Experiments with Barkhausen-Kurz Oscillators Mr. J ohn N . Dyer has described * some simpl e prima ry experiments with the Barkhausen-Kurz type of oscillator wh ich may well serve as an introdu ct ion to their use. In t he fo llowing quoted material th e a bbreviation "BK " stands for "Ba rkh ausen-Kurz," a nd " ha m " means a radio amateur of the t ra nsmi tting variety. "The p urpose of R, is to vary the grid voltage from about 75 to 250 volts. If some other method of va rying t he voltage in small steps is at ha nd t his resistor is not necessa ry. Th e va lue of R, wi ll depend , of co urse, on the voltage of t he power supply used. R, is a small pot ent iometer with which to va ry t he plate voltage from abo ut zero to -10 volts. The plate battery may be a small " C" battery , b ut t he grid voltage had best be supp lied by a "B" eliminator unless storage " B " batteries a re availab le, since the d rain is reall y too heavy for ordinary d ry-cell " B" batteries . Ra and R 4 are fil a ment rh eostats, one of low resistance for fin e ad justments and t he other of higher resistance for coarse adjustments. The fi la me nt suppl y had best be a battery, bu t may be a.c. if no storage battery is at hand. For 'phone work, however, th e use of a.c. on t he fi la men t will cause abo ut 100% hum modulation. The condensers C, an d C, may be of any convenient value, such as .002-µfd., a nd are arran ged so t hat t hey may be moved along t he Lecher w1res. A few sample values of voltages a nd "'QST , Septem ber 193 1.

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THE MANUAL OF ULTRA SHORT WAVE RADIO

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always the same it is conve nient to be able to change t he outpu t voltage of the amplifier so as to pu t t he most power int o the load . This can be done easil y if the output transform er has a tapped secondary such as is shown in the National diagram herewith. This transformer has another design feature, C 1 a nd Li can be omitted, a nd t he plate current of t he ' 10 tube-to-be-modu lated (that is the r.f. tube) can simpl y be fed through the transformer secondary. The wire is large enou gh to prevent a ny noticeable heatin g a nd the a udio curve is changed on ly in that it cuts off at 100 cycles instead of 40 cycles - and one

II

NATIONAL'S TRANSFORMERS AND CONSTANTS

Bl Input 1to1 20 hy Primary resi stan ce 150 ohms Secondary resistance 200 ohms V oltage Rat io

Pri mary inductanc e

Primary turns Secondary turns

Inter-wind ing insulation

BO Output 1 .66 to up to 1 to 1 20 hy 115 ohms 90 to 160 2 x 1000 1225, 1415, 1 5,580, 1730 a nd 2000 4000 volts a .c.

ance there has been introduced the type '46 tube, which is an odd 2-grid affair t hat can be turned into a high-mu or low-m u t ube by merel y connecting its extra grid - but the accompanying diagra m should make everything clear. In the first position the tube is being used as a "Class A" or non-distortin g a mplifier. I ts outer grid has been tied t o t he plate so as to produce a low-m u tube useful for such work. In the pushpull stage t he two grids have been t ied together, producing a tube of such a high mu that no bias whatever is required, t he tube being nearly cut off without it. Thus it can be used "Class B" wi thout

GENERAL RADIO TRANSFORMER CONST ANTS

Voltage Ratio

292-A (input) 2928 (output) Ta T, 1 to 1 1 .7 to 1

L,-M.+L.... t 30Ko...;.. C.row-' M,.tl.-t ZMfd

Primary inductance

at 60 cycles Primary res istance

Secondary resistance Ma x. d.c. primary volts

70 hy 620 ohms 780 ohms 27 5

40 hy x 2 230 ohms X 2 520 ohms 700

3 .000 4 .000

DIAGRAM OF C LASS

vVh en it is necessary to work in to some other sort of a load, such as a different tube or t ubes, it is convenient to have a n output transformer that is tapped . In the diagram of the National "Class B" amplifier such a transformer is shown. It is strongly recommended that one attempt to forget about the business of im pedance-matching as t his somewhat loses its significance when using a distortion-amplifier. I t is better to think of the pla in resistance of the load. For instance if we are modulating a '10 t ube which is runnin g at 500 volts d. c. it is clear that our job is to supply to t hat tube half as many a ud io watts. Since the resistance of t he load is not

·5·

AMPLIFIER

doesn't need that for speech! The connection of the d otted line MAY be used but the separate plate suppl y is still to be p referred if one works t he stage "Class B".

The '46 Tube The main snag in th is sort of an amplifier is of co urse the need for battery bias fo r the Class B stage. A resistancedrop bias of any sort d oes not a nswer very well as it varies with t he wobbling plate current. T o get aro und t his nuis-

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tron is not at a ll readily available, altho ugh a thoroughly good fonnof it is in existence- in fact , two of t hem. The regenerative oscillators, when taken down to 75 cm. tend to become eit her unstable or low in output, and the BarkhausenK urtz devices are inherently lowpowered a nd unstable to the last degree. One is led back to the 1925 a nd 1926 wo rk of J ones and Lyma n (see page 64) in which a regenerative oscillator was run at 1Y, meters and the 2nd harmonic a mplified, or to t he even simpler device of merely employing a n antenna tuned to t he half-wave, without bothering to amplify it, as in the photos to the upper left. Coupled with a sui table reflectro reflector, as shown on page 49, such a transmitter does not do badly. In the briefest of tests some 1500 feet we re

*

48

*

THE MANUAL OF ULTRA SHORT WA VE RADIO

Uda's 50 cm . transmitter which worked phone 10 km . and i.c.w. 30 km .

•

Simpler reflectors of sheet metal may be made as was this one, used in the experi- . ments of Dr. Esau, referred to in chapter 5. Another construction is shown on page 5

•

The oldest of all radiophones is the lightbeam type - fa r older than radio . A modernized form is here being shown by Dr. V. K. Zworykin, and a simple working diagram of the transmitter appears below. The complete system is suggested on the next page. With the visible light filtered out the system works on the "heat" end of the ultra-short-wave spectrum

.

OUTPUT= --ii A T UBES . PUSH-PULL

2 M FD .

CD ' AUDIO AMPLIFI E R

/

80

H.11

I

/ IMPEDANCE ADJUSTI NG T RANS FORM ER. OUTPU T · 20.000 OHMS. INPUT= 2.500 OHMS

THE MANUAL OF ULTRA SHORT WAVE RADIO

MI LLI AMM ETER . -' (OPE RATE AT ABOU T 10 MI C.S)

2 M FD. _-,,,50.000 OHMS

*

49

*

Chapter 8

• • •

•

Receiving 1n the Ultra-Short Mr. Dana Bacon testing the 5-meter converter of page 54 in conjunction with an automobile broadcast-wave receiver which is serving as the i.F. and audio system of the resultant superheterodyne

t he preceding chapter, t his one concerns itself wit h t he t ransmitting amateur 5- and %· meter bands, and nothing else. The sketch below suggests why t he nearhea tend of the spectru m may properly be dropped out, while the chart on page 9 will suggest t hat for the moment much of the te rritory seems more attractive to the laborato rian a nd the pure scientist than to the man primaril y interested in talking to someone by radio. The %- meter band will be taken up first, because for the moment that is the shorter story. \Vithout fur t her formality we quote again from Mr. J ohn Dye r's QST a rticle; beginning with that part in which a receiver of t he Barkhausen-Kurz type is described: "The circuit of t he receive r is q ui te similar to that of ' the tra nsmitter and is shown on page 51. The same type tu be as in the transmitter may be used in t he receiver if desired, although the '99

C

Wave Bands

and similar tubes will be found satisfactory in certain cases. The choice of tube will, of cou rse, determine the size resistances used for the control of voltages . For small t ubes 'B' battery supply will be satisfactory sin ce the drain will be low. "For tuning it is conve nient to have t he Lecher wires arranged so that t heir length may be varied. This may be done by allowing the t ube socket to slid e in guides with flexible filam ent leads and with the Lecher wires of telescoping construction, with about No . 6 to 8 wire slidin g inside of copper tubing. Since the Lecher wires may be run on a ny odd quarter wavelength they may be made to cover a large wave band . As a ty pical instance, their length may be made to vary between 10 and 20 inches. Condenser C, is variable a nd furnishes a simple control of t he wavelength over a limited range. It may be large, about 250-µµf d., since t he t uning is not at all critical.

" Super-regeneration should be used on the receiver and a low-frequency oscillator should be coupled to the plate circuit. The coupling condenser (w hich will call C,) should be variab le or 'plu g-in .' It will be small , probab ly near 100-µµfd., depending on the strength of the low-frequency oscillator. The tube in th is oscillator may be anything that is available as may be the coils a nd condensers used in it sin ce t he frequency is not at all critical a nd may be from 10 to 100 kc.

A

CH

CH

A

In the heat end of the ultra-short-wave spectrum the transmission system reduces to these simple devices, to which only batteries and amplifiers need be added. With suitable filters this arrangement will transmit with either heat or light waves

* 50 *

Basic Form of the Barkhausen-Kurz receivers. Reference to pages 10, 14, 15, 16 and 17 will show its identity with the transmitters in all but power. The rectangles A-A are merely symbols for the collectors, which may actually be rods. The practical receiver is shown on page 51

THE MANUAL OF ULTRA SHORT WAVE RADIO

A.F.AMP.

i~{ -B

+B

The photographs show a 50-cm. Barkhausen-Kurz receiver of Uda, both with the cover removed, and with the complete assembly including the array of directors and reflectors surrounding the antenna, which in this case is 1/2 wave long and terminates inside the set at the detector tube in a manner similar to the diagram, though the latter is from the paper by Dyer. For adjustments see Okabe on "ampli-detectiQn," Proc. I. R. E., June11930

" The simplest coupling me thod is to tie the oscillator and detector filaments together and then to connect C,, just mentioned, from oscillator plate to the junct ion of the R. F. C. a nd the A. F. T. primary in the diagram appearing in the upper right corner of this page. "The antenna for the receiver may be arranged as for the transmitter and, if possible, a parabolic reflector with Yz-wavelength reflector wires with the receiver antenna at the focus being used . The same type reflector will be a great a id if used on the transmitter also. The reflectors also may be made from solid metal sheets. Considerable a.f. amplification shou ld be used on the receiver, since it will usuall y be found to be quite 'qu iet,' a nd at least two stages may be used. "

This is an appropriate place at which to say that the "background" noise of an ultra-short-wave receive r seems to mean less than nothing as to its sensitivity, especially in super-regenerative receivers and those of the detectoraudio type. A listening test is the onl y sure test. 11

Reflectors and Directors" \/\Tith insensitive receivers, a nd a %-meter wave that is easil y screened off, one must do all possible with the antenna. The good old fashioned sheetme tal Hertz reflector, model of 1886, is still the best thing we have, just as in the case of the transmitter (see page 49), but its weight encourages the substitution of wire reflectors which are miniatures of those shown on pages 22

a nd 23 - or even the cut-down form of page 55. These things help amazingly, sometimes increasing the signal audibili ty as much as 10 to 1 for the simple form of page 55 and as much as 50 to 1 for the forms of pages 22 and 23. In addition one may take advantage oi the very clever " directors" of Yagi, being sure to read his paper in the June, 1928, Proceedings of the Institute of Radio Engineers. These " directors" are a row of wires slight ly less than %-wave long set in a line TOW ARD the sending station. For best effect they are spaced % of a wavelength apart, although the one nearest the receiving antenna may be omi tted, sometimes with advantage. If t he a nten na is vertical t he directors must of course a lso be, and their length should be about .43 to .44 wavelength,

RFC 70 !st. A.udio T.ube

The autodyne-detector-plus-audio arrangement has some merit at 5 meters, but tends to be noisy and to change its tuning when regeneration is adjusted. The former is ameliorated by the construction of diagram B, while the latter is decreased by the arrangement C, though a much neater expedient is C. H. West's control which uses a noiseless filament rheostat of a resistance wire helix into which a short-circuiting screw is threaded. The 112A tube is most suitable. Ci may have a maximum capacity of 3 microfarads (see page 52) and L may be one turn 1" to 11/2" in diameter. L2 same, or 9 turns, 1/2" dia. C2 not predictable

+A -B RFC

©

FIG .3

THE MANUAL OF ULTRA SHORT WA VE RADIO

8"0et.

A-

B+Amp.

*

51

*

T

I[

'J8 PENTODE

Ill~

"'

2 +45

+90

R"~

f:p

1300

-

+18 0

In all shortwave receivers the antenna tuning tends to interfere with proper operation, especially when using detector-audio sets. At the left is a circuit used in the National Company's laboratory for preventing this difficulty. At the right is the Telefunken method of using a resistance "pad" as a coupler. Rand R" are each of 500 ohms, making the antenna aperiodic, while the 300 ohms of R' provides loose coupling , C is uncritical but small. Ci and its shunt may be replaced by a condenser such as the type 35-70 of National or the General Radio type. The receiver is shown on page 27

in other words 86 to 88% the length of the halfwave antenna - although the same directors without change will work with a fullwave antenna - i.e., one a wavelength long. The received current has in some cases been increased 10 to 15 times wit h the aid of directors. If t he receiving antenna is horizontal - and this should a lways be tried if signals seem poor - the directors should be a trifle longe r, a trifle over .45 wave-

A small isolantite-insulated va riable condenser for 5 and 3J,i meter receivers and low-power transmitters

*

52

*

length, or 90% of th e halfwave antenna length. Recalling what was said in chapter 7 about the effect of the earth it is seen t hat the receiver had best be at some height above ground, 30 feet giving most of the possible advantage unless obstructions are to be hurdled - for t his is fa irly pure "optical " transmission and careful aim , plus clear view, seem essential. The t unin g of the receiver is of course a ted ious business, and had initially best be don e near the transmitter until one at least knows that one is NEAR the sending wavelength. It is not at a ll hard to miss t he direction or

wavelength slightly-and be hopelessly lost. Since the receiver is small and simple it is best to start at the sender and w9rk out a bit at a time. If the signal is then lost it is still possible to go to t he fina l position a nd start fis hin g with so me confidence. T he second-best collector is a simple large antenna which has its top well up in the air. This is used wit hou t regard to t unin g and in most cases it is suffi cient to run the antenna by t he receiver at a distance of 2 to 10 cm ., if it gro unded, or at even greater distance if the encl is free. The a ntenna may

The upper photograph is that of a 1925 super-regenerative ultraudion by Frank C. Jones. This was used at 11/2 to 10 meters and it is interesting that a copy seems today to be a good receiver. The diagram is a slight modification of an excellent one by C. C. Whitehead, the receiver being shown on page 6. The detector osci II ates at two frequencies, one ultra-short wave as determined by Ci, C2 and the upper coils, the other supersonic as determined by ( 5 and its coils. ( , is a mica condenser of .0001 capacity, Ci a low-loss tuning condenser of about 2 micro-microfarads max . (.000002 mfd.) and may be replaced by the type at up111C per left with all but 2 plates removed, and spaced 1f,i". C, is .001 (because of the supersonic freq.) while ( , is ti +45 .0003 or whatever is needed to produce 20,000 to 100,000 cycles. The rheostat R controls the variation-freq. • input. The coil can be of about 75,000 microhenries with the tickler of 10 to 50% as many turns. The receiver at the lower left is also a super-regenerative type after Ross Hull. It uses a '37 triode (rear) and a '38 output pentode as an audio amplifier (right front). The variation-freq. is provided by the separate '37 triode oscillator at the left front, which is coupled to the detector by feeding the plate supply through the plate coil of the oscillator. The r.f. portion of the circuit is like that of the other two except that the tuning is done with C2 and Ci is a "trimmer" used to adjust to the band. In all three sets the antenna is connected to the grid through a trimmer condenser

THE MANUAL OF ULTRA SHORT WAVE RADIO

'

C9 00005 MF"D.

V< -l2A

"

r---- ------'

SH IELD

·-1'

INOICATCS CONNECT ION

:

,'/ M~~~tg~A~~IS ~ W°

L"3 t--'~---€---.,.-'---l R F: CH Oli as large and have perhaps 9 turns which must be adjusted by trial. The first tickler oscillates more easily - and gives more t unin g effect from the regeneration control. The \Vest device is recomm ended to avoid this. The gridleak as a rule must have a very high or very low resistance for plate suppl y voltage control - but a normal one for fil ame nt control.

Super-Regeneration Band in Meters

Coil No.

L (ant.)

L (sec.)

80 40 30 20 15 11 9 7 5

1 2 3 4 5 6 7 8 9

6 6 6 5 5 4 4 4 4

22 14 8 6 3% 4 3 2% 2

(r.f.)

Ls (Det.)

L, (tickler)

Diameter (inches)

21 14 8 6 3% 4 3 2% 2

21 13 7% 5 3 4 3 2 2

6 6 4 4 3% 4 4 4 4

2 2 2 2 2 1 1 % %

L,

TICKLERS. - For coils Nos. 1 to 5 inclusive the winding Ls is of No. 28 enameled wire, wound 30 turns ·to the inch. This winding is placed % in. from Lz. For coils Nos. 6 to 9 inclusive the L, winding is of No. 22 d.s.c., spacing to be adjusted until the frequency range is correct. OTHER WINDINGS. - For coils Nos. 1 to 5 inclusive the windings L, L1, L, and Ls are of No . 22 enameled wire, spaced 18 turns to the inch. For coils 6 to 9 inclusive use No. 22 d.s.c. unspaced. OTHER CONSTANTS. - C, Cs and C. 2, Cardwell 169E with stator split. Shield box 101/2" high, 9V2" fore and aft, 33" long divided into rooms (starting at left) 11 ", 9%" and 11" long.

To avoid t hese t inkerings one may t hrow the t ube into ha rd oscillation and then use super-regeneration to provide periodic excursions t hrough the sensitive point . The illustrations a nd captions on page 52 cover t his type of receiver for practical purposes.

T. R. F. at 5 Meters We have so long been told that t. r. f. amplification is not possible at ultrashort waves that most of us have believed it. The accompany ing diagram of Mr. Thomas R. Marshall's t. r. f. receiver, a nd its performance as related in Chapter 5, should do something to correct the im pression . Actually the '24 tube is worst at abo ut 13 meters, while a t 5, with thoughtful design, gains of 5 per stage have been obtained by Boyd Phelps and higher gains are certainly possible with the '57 a nd '58 tubes which appear to have been designed with 5-meter television in mind.

;

•

greatly upset the wavelength of t he receiver and t he T elefunk en input "pad" shown in this chapter may be of considerable help. I t should of course be a pa rt of the receiver, and be left in

A 5-meter r.f. choke

it even when not using the large antenna, so that some calibration may be retained. Turning to the 5-meter band we find it possible at once to introduce much more varie ty, partly because there is so much more history in the way of experimental reception . All of t he present types have been with us at least 7 years, hence some progress has been made in ironing out the difficulties. The rather cranky nature of the plain detector-audio 5-meter receiver when adjusted to good sensitivity, has caused

THE MANUAL OF ULTRA SHORT WAVE RADIO

National's Shield for the '57 and ' 58

*

53

*

A unique 1-tube 5-meter converter developed atthe National Company's laboratory, but superseded

The r.f. pentode of the variety represented by the '57 and '58 is "so meth in g else again" from the aud io-o utpu t type such as t he '47. These t ubes have a.c. filaments a nd in usin g t hem in t he circuits here shown it is therefo re necessary to modify the circui ts (see p . 55 ) or to use d.c. on the fil a ments. Three will operate satisfactoril y in series on a 6 \'. storage battery. Briefl y, the two new t ubes are of the same general fami ly, but t he '58 is of t he va ri a ble mu type. Both have "su ppressor" grids between the screen an d plate preventin g damage from the rather common co nd ition in which the screen momentari ly is more positive than t he plate. The construction suggests t hat the tube should be ma teriall y better than t he '24 for 5 meter r.f. a mplification t hough it may be ment ioned in passin g that gains of about 3 to 5 per stage are possible with the '24 used carefull y. As

If One Wishes To Try A.C. Operation - There Are the '57 and '58 Pentodes and the Improved '27- i.e. the '56 Type '56

Type '57

Type '58

2 .5 2.5 2 .5 Filament Potential - Volts 1.0 1.0 1 .0 Filament Current - Amperes 250 250 250 Plate Potential - Volts 100 100 Screen Potential - Volts -13 .5 -3 -3 Control Grid Potential - Volts 5 .0 8.2 2 .0 Plate Current - M. A. 1.0 3.0 Screen Current - M. A. (nominal) 9500 1,500,000 800,000 Plate Impedance - Ohms 13.8 1500 1280 Amplification Factor 1450 Mutual Conductance - Micromhos 1225 1600 at-40 Volt Grid Bias - Micromhos 10 at-50 Volt Grid Bias - Micromhos 2 Small 5 prong Small 6 prong Small 6 prong Base 41,4" Overall Height 4'l's " 4'l's " Improved '27 r.f. pentode r.f. pentode variable Kind of Tube mu.

was prophesied in this pape r (March) the trend away from super-regenerative recept ion has begun - and if the '5 7 and '58 are not as suitable as we t hinkt here will be another t ube. Th e '57 is a good bias detector, when worked with a one-quarter megohm co up li ng resist-

a nce, a grid voltage of min us 6 and everything else as in t he t able above. T he '56 can be read off from the table a nd the curves. I t is a n imp roved '27 , taking less current, using less space - and doing a better job. Why say more?

The next step, a 2-tube converter of National design . Like most 2-tube converters the performance depended considerably on the input circuit of the broadcast receiver

•

*

54

*

THE MANUAL OF ULTRA SHORT WA VE RADIO

~:

A BROADCAST G RECEIVER

National's 5-meter superheterodyne converter, derived from the experimental forms on page 54. The usual output circuit (upper right) was abandoned because of the uncertainty of getting an adequate load to produce efficiency . Broadcast receivers with tunable input circuits or high impedance primaries do well, others do badly with such a circuif. The impedance-matching tube (237 fixt i.f.) was therefore added. The plate impedance of this tube is only a few percent of that shown by a biased 'detector, hence it is an impedance adjuster and in addition it supplies a ga in of about 7 at the working frequency. The usual frequency wanders of a 5-meter superheterodyne are largely avoided by two expedients, the tuned circuits are bu ilt on isolantite and R-39, also they are electron-coupled (see page 19) to their loads. The antenna is loosely coupled through the small capacity C to minimize the effects of its va ri ations, and in the present form of the co nverter a resistance T-pad is used as shown on pages 52 and 57. The d iagram for d.c . tubes is shown, but the a.c. form is also commercial

OUT PUT 5,000 TO BROADCAST

The diagrams are intentionally shown in their d.c. form, not only because the battery is q uieter than t he line, but a lso because the 6-volt t ubes a re especia ll y good for 5-meter work . All of the circuits are wo rkabl e with regula r '27 and '24 tubes, though t he new series of tubes, shown on page 54, is preferable to them because they have a smaller fi lament curren t a nd seem less incl ined to hum or crackle, and also for t he reason s stated alongside of t he table of constants. The '57 wou ld seem to fit especiall y well into t he Marshall receiver of page 53 , where its po rtrait appears, - with overcoa t . The changes to be made in t he circu its in going from d.c. to a.c. are reasonably obvious. Since the d .c. forms get t heir biases from the filament-vo ltage drops it is necessary to provide a new bias when t he fi lament is cut away from the emitter - or cathode. At first it is most advisable to use a C battery an d poten tiometer. After everyt hing else has been cured, there's t ime to start usin g t he ordinary fo rms of bias thro ugh cathode resistors or resistors in t he negat ive B lead. In usin g a circu it of the Dow electron-co upled type as shown on pages 54 (lower), 55 and 57 it m ust be noted t hat at 5 meters t here is strong capacity co uplin g between t he fi lam ent a nd emitter. Both must t herefo re be "off gro und" at radio freque ncies, sin ce t he cathode is un-

I

RECEIVER

A- B-

B+

avo idable " up in t he air" in these circuits it fo llows t hat the fi lament m ust be fed- and ampere - t hroug h good 5-meter chokes. T he bias arrangement, the bypassing from cathode to filament (one side or both) a nd the location of the hum-adj usting potentiometers m ust be worked out fo r each individual construction, si nce other t hings are fu ll y as important as t he circu it diagram in dete rmining the hum effects. T his is sim ply a matter of systematic t rial. As a part of t he experimenting t he tubes shou ld be exchanged , both for t hose of other makes, and fo r diffe ren t individ uals of t he same make. In ge neral t he cheaper t ubes a re noisier.

Oiredion. of Send inJ Sta f i an

As loras

)./2

'-/2

.4s far as