Ii -E HRH Niws CHART THE MIX -SELECTOR 9 NOVEMBER-DECEMBER, 1956 VOL. 11-NO. 6 CONTENTS. ebeficrde TUBES. see pages 4 and 5. AMATEUR BAND SIGNAL

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1 ebefcrde TUBES -E HRH Nws 9 NOVEMBER-DECEMBER, 9 VOL. -NO. THE MX -SELECTOR SSB 'GENERATOR SSB SGNAL CHART AMATEUR BAND ' C OSCLLATOR C SGNAL SSB. SGNAL see pages and. atch your sgnals when desgnng that new mult -band SSB excter or heterodyne -type VFO for your present C or AM transmtter. Our MX -SELECTOR chart explans why sgnal frequences employed n heterodynng must be carefully selected to avod the transmsson of spurous sgnals along wth your desred sgnal. Examne our typcal sgnal combnaton examples-then try workng out your own deas on logarthmc graph paper! CONTENTS

2 SNGLE-SDEBAND BACKGROUND The rapdly ncreasng nterest n sngle-sdeband transmsson and recepton on the amateur bands focuses attenton on the basc dfferences between snglesdeband suppressed carrer transmtters and the old more conventonal RF system used n C and AM transmtters. A smplfed block dagram of the usual AM or C rg, Fg., shows the RF tube lneup startng wth an oscllator, often followed by buffer or harmonc amplfers whch then drve one or more amplfer stages at the output frequency. Modulaton usually s appled to the fnal RF amplfer stage n one of several ways whch dffer manly n the amount of audo power requred for the modulaton process. OSCLLATOR HARMONC AMPLFERS CLASS C POER AMPLFER, ANTENNA Fg.. Block dagram of a typcal mult -stage transmtter to whch a C or AM system may be connected. GENERATNG SNGLE.SDEBAND SGNALS hat are the "sdebands" usually assocated wth voce modulaton of a transmtter? Bascally, they are groups of rado frequences whch result from mxng (or modulatng) a fxed rado frequency sgnal wth one or more audo sgnal frequences. These sgnals add to and subtract from the fxed frequency to form the above - mentoned groups of closely related rado frequency sgnals both lower and hgher than the fxed frequency. The number of ndvdual sgnals present n both sets of sdebands at any one tme depends upon the number of ndvdual sgnal frequences present n the modulatng sgnal. Probng the mysteres of present-day sngle-sdeband technques brngs forth a multtude of other terms such as: sdeband flter, phase -shft network, balanced modulator-etc. Understandng sngle sdeband s further complcated by menton of two systems of generatng a sngle-sdeband-suppressed-carrer sgnal (whch we wll call SSB n the balance of ths dscusson): () the flter system, and () the phasng system. n both systems, SSB sgnals are derved from ampltude -modulated sgnals. n the flter system, an ampltude -modulated sgnal s passed through a flter whch attenuates one of the two sets of sdebands characterstc of ampltude modulaton. The phasng system conssts of two ampltude -modulated systems combned n such a manner that one set of sdebands s renforced whle the other s cancelled. n ether system, t s customary to balance out the so-called carrer from a sgnal that would otherwse be a completely standard ampltude -modulated sgnal. hen properly adjusted, both systems wll delver the same type of output sgnal. Obvously, the flter requrements n that system are qute strct, snce all desred sgnals n one set of sde frequences must be passed, yet the sgnals appearng n the unwanted set of sde frequences should be attenuated at least 0 db (000 to n power) or more. The requred order of flter selectvty s most easly acheved at frequences below 00 klocycles. Thus, many flter -type SSB amateur transmtters now on the ar have the SSB generator crcuts operatng on 0 klocycles, usng ether a mechancal flter, or a lattce - type flter made from quartz crystals. n the phasng system, the sgnal can be generated at any desred output frequency, but t s nconvenent to change frequency easly. n fact, t s dffcult-that s, cumbersome and expensve-to generate an SSB sgnal at a number of chosen frequences and_ select one by bandswtchng wth ether system. A further lmtaton n obtanng an SSB output sgnal on several amateur bands n both flter and phasng systems s that harmoncs of the SSB generator cannot be used. The reason s that frequency multplcaton depends upon non-lnear operaton of the multpler stage, and such operaton ntroduces ntolerable dstorton to a sgnal whose character s already establshed, such as an AM or SSB sgnal. e now have ndcated, frst, that components are not readly avalable for a flter -type SSB generator desgned to operate drectly on an amateur band; second, that the phasng system can be used at any desred narrow band of frequences, but does not lend tself to convenent bandswtchng; and thrd, that harmoncs of the SSB generator sgnal cannot be used. The really practcal soluton to the band -changng and adjustable -frequency SSB generator problem, for the home constructor, s to employ the same prncple used n superheterodyne recevers. That process s to heterodyne an SSB generator sgnal, whch may be outsde the amateur bands, to the desred amateur frequency. The block dagram on page shows the two sgnal generatng stages connected to a mxer stage. FREQUENCY CONVERSON Frequency converson, also known as heterodynng, s smply a process of combnng two sgnals of dfferent frequency to form two new addtonal sgnals havng frequences whch are, respectvely, the sum and the dfference of the two orgnal sgnal frequences. The crcut n whch heterodynng takes place s usually called a mxer, converter or modulator. (They are essentally the same thng.) There are many types of mxer crcuts, but most wll generate harmoncs of both frequences beng appled to them even though the harmonc content of the nput sgnals s very low. Thus, many sgnal frequences can be present n the output of a mxer stage-the two nput sgnals, ther sum and dfference sgnals, and the harmoncs of both nput sgnals. All sgnals except the one desred output sgnal frequency must be consdered as spurous sgnals. Therefore adequate precautonary measures must be taken to prevent these spurous sgnals from appearng n the transmtter output. An mportant step to ensure adequate suppresson of spurous sgnals s to have at least two hgh -selectvty tuned crcuts resonant at the desred output frequency n the stages followng the mxer crcut. f each of these tuned crcuts has a "Q" of 00, spurous sgnals whch are 0 per cent lower or hgher n frequency than the mxer output sgnal wll be attenuated more than 0 db (00,000 to n power). Spurous sgnals wthn 0 per cent of the output sgnal frequency wll be attenuated much less. Practcally speakng, nether of the mxer nput sgnal frequences nor ther harmoncs should fall wthn ths 0 -percent range or they may appear along wth the output sgnal to an apprecable extent. Snce t already has been ponted out that most mxer crcuts wll generate harmoncs of the nput sgnals, these harmonc frequences also should not fall wthn 0 per cent of the desred mxer output sgnal frequency. deally, the best way to avod spurous sgnals resultng from harmoncs of the nput sgnals s to place both mxer nput sgnal frequences hgher than the output sgnal frequency. Ths cannot always be done, especally when convertng the output from a flter -type SSB generator, whch usually operates below 00 klocycles, to the assgned amateur frequences. Snce the phasng -type SSB generator operatng frequency s not smlarly restrcted, the sgnal may be placed hgher n frequency than the amateur band on whch output s desred. n practce, ths s not strctly followed, snce an SSB generator sgnal frequency n the.8- to 0 -megacycle range s usually chosen for -, - and 8 -megacycle transmtters.

3 USNG THE MX -SELECTOR CHART e hope the old sayng, "One pcture s worth ten - thousand words," apples equally to the MX -SE- LECTOR chart on pages and. However, a bref lne - by -lne explanaton wll he gven to clarfy these typcal examples of sgnal frequences used n heterodyne - type SSB excters. The "LEGEND" on page pctures the marks used for dentfyng mxer nput and output sgnals as follows: Fxed frequency nput sgnals are shown as narrow vertcal black lnes. Second, varable frequency mxer nput sgnals are shown as black blocks whose wdth s ndcatve of the frequency range covered. Each fundamental frequency sgnal s dentfed wth a fgure "," and the harmoncs by numbers representng ther order. The heght of the lnes and blocks decreases as the harmonc order ncreases to llustrate the decreasng relatve mportance of the hgher order harmoncs as spurous sgnals. Frequences from. to 0 megacycles are numbered on lne and ndcated by vertcal lnes runnng down the chart. Ths frequency span covers most amateur bands on whch SSB technques presently are employed. The U.S. amateur radotelephone segments n each amateur band are dentfed by the sold black blocks on lne, whch then are carred down the chart n grey shaded bands. The FEEDTHRU DANGER ZONE, prevously descrbed under FREQUENCY CONVERSON, s marked by the pnk areas begnnng at lne and runnng down on ether sde of each amateur 'phone band segment. The left margn of each pnk area s consdered to be 0 per cent lower n frequency than each 'phone band lower edge, and the rght pnk margn represents a frequency 0 per cent hgher than the upper lmt of the same 'phone segment. Of course these danger zones apply only to the amateur band on whch the desred mxer output sgnal s shown, for each horzontal lstng on the chart. FLTER -TYPE B GENERATOR FREQUENCES Lne shows the harmonc sgnals of a 0. -megacycle flter -type SSB generator, begnnng at.8 megacycles wth ts fourth harmonc. The 0. -megacycle sgnal frequency must be heterodyned to the amateur bands to be useful. Suppose t s desred to operate n the.8-.0 megacycle band wth a 0. -megacycle flter -type SSB generator sgnal. A dfference frequency mxer output sgnal can be obtaned by operatng the other mxer nput sgnal range at.-. megacycles, as shown by the sold black block marked "" on lne. Notce that the SSB generator fourth harmonc sgnal at.8 megacycles s wthn the feedthrough danger zone and may appear n the mxer output. The strength of ths spurous sgnal wll depend upon the type of mxer crcut used. t s clear that a mxer havng extremely low harmonc output s necessary to avod troublesome effects caused by 'the fourth harmonc generated wthn the mxer. The hgh selectvty tuned crcuts whch should follow the mxer stage for the purpose of attenuatng the. -. -megacycle sgnal also wll attenuate the hgher order harmoncs shown by the other black blocks marked "," "," "" and "" on lne. hen a mxer output sgnal n the megacycle range s desred, a heterodynng sgnal ether lower (.-. megacycles) or hgher (.-. megacycles) may be used, as shown n lnes and, respectvely. Note that both heterodynng sgnal ranges (the black blocks marked "" on lnes and ) fall partly wthn the feedthrough danger zone of.-. megacycles. Attenuatng these adjustable frequency sgnals wth a trap crcut s more dffcult than trappng out a fxed frequency, snce one tunng adjustment of the trap probably wll not be effectve over the entre range. n ths case a balanced mxer whch cancels the varable frequency mxng sgnal would be desrable. Snce the heterodynng sgnals mentoned thus far permt operaton on only two bands, the practce followed n many flter -type SSB excters s to agan heterodyne the megacycle SSB sgnal descrbed n lnes and to the other amateur bands n a second mxer stage. A block dagram of a typcal double converson SSB excter s shown n Fg.. Ths varable SSB sgnal frequency, ts spurous sgnals and harmoncs must now be consdered as an nput sgnal to the second mxer, as plotted on lne 8. f an output sgnal from the second mxer n the megacycle range s agan desred, a fxed frequency sgnal of ether.0 or.8 megacycles also should be used to mx wth the megacycle SSB generator sgnal. A.0 - megacycle sgnal would be a poor choce, snce t falls wthn the feedthrough danger zone, but lne 9 on the chart shows that the.8 -megacycle nput sgnal s satsfactory. SSB GENERATOR FRST MXER FRST OSCLLATOR (TUNABLE) SECOND MXER SECOND OSCLLATOR (FXED) AMATEUR BAND SSB SGNAL Fg.. Block dagram of a double -converson SSB excter. Hgh -selectvty tuned crcuts should mmedately follow both frst and second mxer stages to avod transmttng spurous sgnals from ether mxer. For a second mxer output sgnal on.-. megacycles, the second harmonc sgnal of the SSB generator,.-8.0 megacycles, falls wthn the feedthrough danger zone. Ths also happens wth the second harmonc of a. -megacycle mxng sgnal shown n lne 0. One spurous sgnal can be avoded by choosng. megacycles, on lne, for a mxng sgnal frequency nstead. As before, a mxer whch does not generate harmoncs s necessary. On lne, the fourth harmonc of the SSB generator sgnal falls wthn the danger zone for. -. -megacycle second mxer output, but the 0. -megacycle mxng sgnal should not prove troublesome. As ndcated on lne, the ffth and sxth harmoncs of the SSB generator sgnal wll fall wthn the feed - through danger zone when a second mxer output sgnal on.-. megacycles s desred. However, the. -megacycle mxng sgnal requred for ths output sgnal frequency s well outsde the danger zone. Agan, when an SSB sgnal at 8. megacycles s requred, as shown on lne, the seventh and eghth harmoncs of the SSB generator sgnal may appear n the second mxer output. The. -megacycle mxng sgnal appears to be a safe choce. All the foregong examples ndcate that a mxer whch has very low harmonc output, plus a balanced type n some cases, should be chosen. THE 9 -MEGACYCLE PHASNG -TYPE SSB GENERATOR A common practce when desgnng a phasng -type all -band SSB excter s to choose an SSB generator sgnal frequency whch permts the same mxng sgnal frequency range to be used for a mxer output sgnal on ether of two bands. But, ths s not the prmary consderaton, snce a frequency whose harmoncs fall outsde the feedthrough danger zones of any desred operatng band should be chosen. The wdely -used 9 -megacycle SSB generator sgnal frequency s good, but has certan dsadvantages. Lne on the chart shows that the thrd harmonc, at megacycles, falls wthn the danger zone when a mxer output sgnal n the 8 -megacycle band s desred. Agan, sutable mxer desgn s necessary to reduce the severty of ths spurous sgnal. (Contnued on page )

4 FREQUENCY N MEGACYCLES U.S. AMATEUR PHONE BANDS FEEDTHRU DANGER ZONE, ±0% OF UPPER & LOER PHONE BAND EDGE SSB GENERATOR ON 0. MC. (ONLY TH 8 HGHER HARMONCS) z E FOR MC DFF. OUTPUT, TUNE VFO TO.-. MC. FOR MC SUM OUTPUT,. TUNE VFO TO.-. MC. FOR MC DFF. OUTPUT, TUNE VFO TO.-. MC. RESULTNG SNGLE SDEBAND OUTPUT ON.8-.0 MC AND HARMONCS M o FOR MC DFF. OUTPUT, TUNE FXED OSC. TO.8 MC. \ FOR. -. -MC SUM OUTPUT, TUNE FXED OSC. TO. MC. MX -SELECTOR CHART ( ' } 8 9 _ j 0 8 L 0 jam 9 /, t.t, q 8El = ( 8 J r n r \ ' $ FOR. -. -MC DFF. OUTPUT, TUNE FXED OSC. TO. MC. ` z FOR. -. -MC SUM OUTPUT, TUNE FXED OSC. TO 0. MC. - x FOR. -. -MC SUM OUT PUT, TUNE OSC. TO. MC. 0 FOR MC SUM OUT- PUT, TUNE OSC. TO. MC. PHASNG TYPE SNGLE SDEBAND o az x E EXCTER ON FXED 9 -MC FREQUENCY FOR MC DFF. OUTPUT, TUNE VFO TO.0-. MC. ^-. FOR MC DFF. OUTPUT, TUNE VFO TO.0-. MC. j FOR. -. -MC DFF. OUTPUT, TUNE VFO TO.-.8 MC. FOR. -. -MC DFF. OUTPUT, TUNE VFO TO.-. MC. FOR. -. -MC SUM OUTPUT, TUNE VFO TO.-. MC. FOR. -. -MC SUM OUTPUT, TUNE VFO TO.-. MC. FOR MC SUM OUTPUT, TUNE VFO TO MC. l P 0, ', cl` M - - No A. AK / 8 9 M h ll ( Í ) L l j r a 8 / J f 9 0 r - E - t ) a l _,

5 FOR 0- MC SUM OUTPUT, TUNE VFO TO - MC., CONVERT -MC. SSB TO 0 MC. PLACE ND OSC. ON 8. MC. CONVERT 8 -MC. SSB TO 0 MC, PLACE ND OC. ON. MC. SNGLE SDEBAND GENERATOR ON F., FXED 8. -MC FREQUENCY FOR MC DFF. OUTPUT, TUNE VFO TO.-. MC. FOR MC DFF. OUTPUT, TUNE VFO TO.-. MC. FOR MC DFF. OUTPUT, TUNE VFO TO.9-. MC. ] 8 FOR. -. -MC DFF. OUTPUT, TUNE VFO TO MC. t FOR. -. -MC DFF. OUTPUT, TUNE VFO TO z.-. MC. Q x f. -. -MC SUM OUTPUT, Et,' Nt.? a. < J S ( d j l A \ 9 VFO TO.-. MC. FOR. -. -MC SUM OUTPUT, VFO TO.-. MC. FOR MC SUM OUTPUT, TUNE VFO TO MC. SNGLE SDEBAND GENERATOR ON FXED. -MC FREQUENCY FOR MC DFF. OUTPUT, TUNE VFO TO MC. FOR MC DFF. OUTPUT, TUNE VFO TO.-. MC. \ FOR MC DFF. OUTPUT, TUNEVFOT0.-.MC. \ co FOR MC DFF. OUTPUT, TUNE VFO TO MC. FOR. -. -MC SUM OUTPUT, TUNE VFO.0-. MC. z x FOR. -. -MC DFF. OUTPUT, TUNE VFO TO.-. MC. FOR. -.-MC SUM OUTPUT, TUNE VFO TO MC. FOR. TUNE VFO TO T MC. FOR MC SUM OUTPUT, TUNE VFO TO.-.8 MC. LEGEND ` AND HARMONCS CSQ ' AND HARMONCS S g Jl J FREQ ; ::::: 0 S / y M 8 w y Q '. G/ r l _ o m )t S El el d Q Q s r Y-, Q (w MXER DFFERENCE OUTPUDFFREQ, ' Q % J a j L a ` G d e OUTPUTU FREQ t ; l l

6 MX -SELECTOR CHART ( Contnued from page ) A varable frequency oscllator must be used wth ths fxed SSB generator sgnal f an adjustable frequency mxer output sgnal s desred for the amateur bands. The VFO tunng ranges requred for mxer output on.8-.0 and.8-.0 megacycles (.0-. and.0-. megacycles, respectvely) are shown on lnes and. These two examples both llustrate the desrable feature of havng both mxer nput sgnals hgher n frequency than the output sgnal. Two possble mxer nput sgnal combnatons for. -. -megacycle mxer output are shown on lnes 8 and 9. Note that the fourth harmonc of the.-.8 -megacycle VFO sgnal on lne 8 falls wthn the danger zone, so the. -. -megacycle VFO range s a better choce. For a. -. -megacycle mxer output sgnal on lne 0, the VFO tunng range of.-. megacycles may be used. However, the VFO thrd harmonc sgnal at.-.9 megacycles s wthn the feedthrough danger zone. A trap crcut n the mxer output to attenuate ths spurous sgnal s ncluded n one type of commercal SSB excter. Note that lnes and 0 are typcal examples of gettng two -band operaton wth one VFO sgnal range. The mxer nput sgnals requred for.-. and megacycle mxer sum output sgnals (.-. and megacycles, respectvely) shown on lnes and present no specal problems. Or, VFO sgnals n the and megacycle ranges, respectvely, may be used for mxer output on these bands f the stablty of the hgher frequency VFO s adequate. Ths problem s even greater when a 0 -megacycle mxer output sgnal s desred. A VFO range of - megacycles s then requred, as shown on lne. Methods of obtanng a 0 -megacycle SSB output sgnal are shown on chart lnes and. A varable frequency SSB excter havng output on the - or 8 -megacycle bands may be fed nto a second mxer stage from whch the 0 -megacycle sgnal s obtaned. On lne, a sgnal on 8. megacycles, and the SSB excter sgnal on.-. megacycles are mxed to obtan a megacycle mxer output sgnal. On lne, an SSB excter output sgnal n the megacycle range s mxed wth a. -megacycle sgnal to obtan a megacycle SSB output sgnal from the second mxer. Fewer spurous sgnal dffcultes may be experenced wth ths combnaton. All sgnals whch are nvolved n a double -heterodynng transmtter should n themselves be free of spurous sgnals. f not, a pyramdng of spurous sgnals s possble at the output of the second converson stage. OTHER PHASNG B GENERATOR FREQUENCES The thrd harmonc of the SSB generator n the 9 - megacycle range, shown on lne at megacycles, may be shfted so that t falls between the feedthrough danger zones for the - and 8 -megacycle amateur bands by selectng a lower SSB generator frequency around 8 megacycles. The chart shows a good example on lne, 8. megacycles, whch has only the fourth harmonc fallng at the upper edge of the 9. -megacycle danger zone. Ths partcular frequency permts a common VFO tunng range to be used for.8-.0 (lne ) and. -. -megacycle (lne ) mxer output sgnals. Two choces are shown for a megacycle mxer output sgnal. The.--.-megacycle VFO tunng range on lne 8 falls wthn the danger zone, so the megacycle range on lne 9 s better. Look what happens when a low -frequency VFO tunng range ( megacycles on lne 0) s used for a mxer output sgnal n the. -. -megacycle band! The VFO eghth and nnth harmoncs both land n the mxer output range, requrng excellent mxer desgn to avod almost certan trouble from spurous sgnals. Placng the VFO range at.-. megacycles, as shown on lne, avods ths problem. The two VFO tunng ranges requred for sum mxer output sgnals n the.- and 8. -megacycle bands are llustrated on lnes and. Output n the 0 -megacycle band may be obtaned wth double converson sgnal combnatons smlar to those shown on lnes and. Most SSB generator sgnal frequences below megacycles wll have harmoncs fallng wthn several feedthrough danger zones. But, by gong a bt hgher n frequency, to the. -. -megacycle range, all lower order harmoncs except the ffth are n the clear. A frequency of. megacycles (lne ) enables the same VFO tunng range ( megacycles) to be used for mxer output sgnals on.8-.0 megacycles (lne ) and.-. megacycles (lne ). An alternate VFO tunng range (.0-. megacycles) for megacycle output s shown on lne. hen shootng for a mxer output sgnal on.8-.0 megacycles, VFO tunng ranges of ether.-. megacycles (lne 8) or megacycles (lne 9) present no stubborn problems. Careful algnment of the hgh "Q" tuned crcuts followng the mxer s necessary to prevent the second harmonc of the. -. -megacycle VFO range from feedng through. A megacycle mxer output sgnal may be obtaned by combnng the. -megacycle SSB generator sgnal wth ether a megacycle (lne 0) or a megacycle (lne ) VFO sgnal. However, as a.0-. -megacycle VFO s tuned through ts range, the sxth harmonc sgnal wll cross the SSB generator sgnal, and the seventh harmonc wll cross the mxer output sgnal. Obvously, ths combnaton s an excellent spurous output sgnal or "brde" generator, so the. -. -megacycle VFO sgnal s preferable. The sum mxer output sgnals on both the.- and 8. -megacycle bands may be obtaned wth VFO tunng ranges of.0-. (lne ) and.-.8 (lne ) megacycles, respectvely. The only specal precauton necessary wth the sgnal combnatons lsted on lnes to s a trap crcut to attenuate the ffth harmonc of the SSB generator sgnal on megacycles, when operatng the excter on the 8. - megacycle band. DO T YOURSELF SUGGESTONS Although other SSB generator sgnal frequences may be used, choce of one of the followng frequency ranges s suggested for the SSB generator when desgnng an all -band excter wth a mnmum of spurous sgnals resultng from harmoncs of the SSB generator sgnal:.-., 8.-8.,.-.,.-9.0,.-. and - megacycles. hat about a system n whch the VFO sgnal s fed nto a harmonc amplfer, and the 'resultng second, thrd, or fourth harmonc s used as the heterodynng sgnal n the mxer stage? Ths can lead to more complcatons from spurous sgnals than a double converson system. n addton, t multples any VFO frequency drft by the same factor as the harmonc. Generally speakng, the double converson system s preferable when a varable frequency mxer nput sgnal hgher than 0 megacycles s requred to obtan a mxer output sgnal n the -, -, 8-, and 0 -megacycle bands. You can fgure out your own SSB excter sgnal frequency combnatons by: () plottng the fundamental and harmoncs of a tentatve SSB generator frequency on graph paper; () plottng the VFO tunng ranges for obtanng output on each amateur band; and () fllng n the harmoncs of each VFO tunng range to see whether they fall wthn the feedthrough danger zone for the band on whch the mxer output sgnal appears. f ths happens, the SSB generator frequency may be shfted, then new VFO tunng ranges plotted whch wll mss the danger zones. Often, an SSB generator sgnal frequency may be found whch permts the same VFO tunng range to be used on two bands. However, f you fnd a combnaton whch produces a mxer output sgnal on four bands wth only two VFO tunng ranges, then you've really ht the jackpot!

7 fval0 SEEPNG the SPECTRUM ;L0ú Here's an dea whch wll be of nterest to many persons wshng to study for ther amateur rado lcense-also rado clubs whch are conductng or are plannng to conduct an amateur lcense -tranng course. The Rado -Electroncs -Televson Manufacturers Assocaton has recently packaged a unque amateur rado study course, complete wth code nstructon on fve -nch -dameter long-playng records, a handy book of theory lessons and supplementary ads, plus a copy of the ARRL Lcense Manual. The complete course s avalable for $0, postpad, from ther offce, Sute 800, yatt Buldng, ashngton, D. C. Most of you are rado amateurs-devoted to amateursm-a term whch has many explanatons. An excellent statement on ths subject-one whch really hghlghts the unselfsh vew-was recently publshed n a French amateur rado magazne. Our Englsh translaton, whch follows, has not been edted n order to preserve the orgnal edtoral's flavor and meanng: The permanent secretary of the Academy of Scences has affrmed that "The Amateur has a fundamental and ndspensable role n all actvtes." From onr pont of vew n rado, electronc theory has no meanng unless appled electroncs follows. The experments tred and the experences consdered exst only wth the vew of mmedate applcaton. The results, obtaned ought n effect, to he put at the servce of humanty as soon as possble. hether he be aware of t or not, the ndvdual lves by means of a contnual exchange of servces wth ths large famly of humanty. f le attempts to solate hmself, le nevertheless profts from the work of others, wthout gvng anythng n exchange: he becomes a paraste. The spectacular ad that the OM performs sometmes n case of emergency should not make us rget hs permanent and modest utlty. Ths resdes n all of hs actvtes to the extent that he makes them known. One does not expect a flood of brllant results of /tnt, but rather the gentle stream of news whch come from hs patent daly experence. t s n ths manner that technques are perfected and the fronters of the unknown are slowly pushed back. t s pure egotsm to hde n one's staton and never communcate one's deas, schemes, contacts or trals of thngs. t s also to deprve one's self of the lght of that frendly cooperaton whch makes amateursm so charmng. Thus, your work, experments, and research should be made publc at meetngs, expostons and at natonal and nternatonal conferences. t s necessary to know the results obtaned even f they are not brllant. Another OM wll know perhaps how to use them n a better manner. Do not be too personally occuped and look at the results objectvely. hether you lke the lower frequences or UHF/VHF, remote control, antennas; whether you be young or not so young and more or less a slave of routne; avod becomng a robot. Thnk, work and make your efforts known. t s only under these condtons that Amateursn wll develop. L. Aubry, FBTM Rado REF Aug./Sept., 9 That closng date (January, 9) for nomnatons for the 9 Edson Rado Amateur Award s approachng fast, so now s the tme to name your canddate! The judges can consder only those canddates nomnated by letter from you. Many publc servce actvtes qualfy a person for Award recognton. Check the partal lst below, then wrte a nomnatng letter and mal t to the Edson Rado Amateur Award Commttee, General Electrc Company, Schenectady, N. Y. Here are typcal actvtes that prospectve canddates you know may have performed: Emergency communcatons work n a dsaster, such as flood, hurrcane, tornado, or exploson. Relayng messages from remote ponts for the beneft of solated servcemen and cvlans. Cvl -defense organzaton work. Tranng novces, or otherwse encouragng and assstng amateur actvtes and nterests. Helpng amateurs or others wth ther specalzed problems through professonal knowledge. Publshng a book or other lterature that contrbutes to amateur or general scentfc knowledge or procedure. Helpng physcally handcapped amateurs or others. Desgnng and constructng rado equpment for use by persons n remote parts of the Earth, who do not have access to regular commercal communcatons channels. eather reportng; rado assstance to state or local traffc and polce authortes; co-operaton n forest -fre preventon and control. P.S. Award rules were publshed on page of September, 9 QST and CQ magaznes, or, drop me a lne askng for a copy. HAT'S AVALABLE? FREE-some back ssues of G -E HAM NES, 9 and later-ssb PACK- AGES-tube techncal data sheets (specfy type numbers)-descrptve booklets. AT COST-G-E HAM NES maled to your address by subscrpton, $.00 per year-log FORM QSL CARDS, package of 00 cards, $.00, postpad-g-e HAM NES Second Bound Volume, contanng all ssues from 9 through 9, plus a handy cross ndex, $.00, postpad. Has your amateur rado club heard t yet? mean the tape recordng of the 9 Edson Rado Amateur Award presentaton ceremony whch wll loan to your club secretary or program charman upon request. Postage wll be pad both ways, but please wrte at least a month n advance of the date on whch your club wshes to play the program. smply ask that the tape be returned promptly so that t can be scheduled for other groups-and my thanks for the splendd cooperaton receved from all clubs who have thus far requested the program..ulna,vuy

8 TECHNCAL. TDBTS HAT ABOUT MXER CRCUTS? Mxers (modulators) can have smple or complex, sngle -ended or push-pull (balanced) crcutry, operate at low or hgh level, and employ dodes or mult -element tubes. A sngle -ended dode mxer (the crcut used n most UHF televson tuners) and the balanced dode mxer (two of them are used n the SSB, Jr.) are more foolproof than mult -element tube mxers, but no power gan can be obtaned, and the dode mxer s lkely to have hgh harmonc output. Ths s the prce of smplcty plus low dstorton n the output sgnal. Although a trode tube may be used as a mxer, both nput sgnals must be appled to the control grd, or to the control grd and cathode, respectvely. Even though generaton of harmoncs n a trode mxer s apt to be lower than n a dode crcut, the operatng condtons must be carefully controlled to avod dstorton of the output sgnal. Ths apples equally to pentodes and the mult -grd tubes desgned especally for mxer servce n superheterodyne rado recevers. Mxer crcuts for these tubes usually feed each mxer nput sgnal nto a separate grd, where the sgnals are combned n the tube's electron stream. A crcut tuned to the desred output sgnal frequency s connected to the tube's plate. Each of the mxer tube's nput sgnal grds should operate n the Class A regon for lowest harmonc output, snce the ampltude of nput sgnal harmoncs generated n the mxer depends on the operatng pont and ampltude of the nput sgnals. Even though a pentagrd mxer stage requres crtcal adjustment for mnmum dstorton, t wll have a lower harmonc output when properly adjusted than the other types of mxers. Snce normal Class A amplfer effcency s only -0 per cent, and that of a Class A mxer s even lower, much of a properly operated mxer tube's nput power s dsspated nstead of appearng as output power. For ths reason, a hgh-level mxer tube wll have much lower power output than the same tube n a lnear amplfer. Even the mnute power output from a low-level mxer stage can be brought up to a respectable level n one hgh gan lnear amplfer stage. Even though sngle -ended mxer crcuts are wdely used, the balanced mxer crcut offers the nherent advantage of cancellng the fundamental and certan harmoncs of at least one, and possbly both, nput sgnals. Usually ths type of mxer can be precsely balanced for maxmum attenuaton of the fundamental or a partcular harmonc of ether nput sgnal, but not all smultaneously. n general, a properly operated balanced mxer usng pentagrd tubes wll have low harmonc generaton propertes, but other mxers wll not, whether balanced or otherwse. The actual crcutry for a pentagrd balanced mxer may have both pars of nput sgnal grds connected to separate push-pull tank crcuts, wth the tube plates connected n parallel to a sngle -ended tuned crcut, or one par of grds may be connected n push-pull, the other par of sgnal grds n parallel, and the plates connected to a push-pull tank crcut. The mxer nput sgnal on whch cancellaton s desred should be appled to the sgnal grds through the push-pull tank crcut. However, under certan condtons, t s possble to cancel out the desred output sgnal! Any balanced mxer may become unbalanced due to component agng and operatng voltage changes, so a mxer balancng adjustment should be provded n the crcut. Fnally, the pentagrd tube balanced mxer crcut may help reduce those spurous sgnals whch cannot be readly attenuated wth specal trap crcuts, or by dependng on the skrt selectvty of cascaded tuned crcuts at the mxer output frequency. TUBES GT. HAM S G -E Electronc Tube Dstrbutors VOL. -NO. publshed b-monthly by ELECTRONC COMPONENTS DVSON GENERAL (JfL Schenectady, N. Y. ELECTRC n Canada CANADAN GENERAL ELECTRC CO., LTD. 89 Duff ern St., Toronto, Ontaro E. A. NEAL, JZK-EDTOR NOVEMBER-DECEMBER, 9 -,,, - TS,,,T-_ ' a -s.-. : C. STREET LYvt,, MASSACHUSETTS Form Requested