•

. '

.,.

,•CQ

Reviews:

The Millen 92200, "

2 KW TransmatchBY WILFRED M . SCHERER,' W 2AEF

M veil of the present-day transmittinggear is designed with a fixed output imped­ance for matching to loads of 50 ohms or so.Others may have an adjustable output formatching over only a limited range such asfor essentially non-reactive loads of 25-100ohms. As a consequence, in such cases, maxi­mum outpu t from the transmitter or sufficientloading for proper operation of a linearamplifier may not be possible where the loadimpedance falls outside the matching rangeor where such loads are reactive and thes.w.r. seen by the transmitter is greater than1.5 or 2 to I. These situations may existwhere large frequency excursions are madeover a band, a multi-band antenna is in useor other cases where the transmission linecannot be properly matched or be thus main­tained for presenting a low s.w.r. to thetransmitter.

Under these conditions, it would there­fore be desirable to employ some externalmeans of providing the proper load for besttransmitter performance. An expedient foraccomplishing this is an impedance-matchingantenna coupler, A number of such affairshave been described in amateur literatureand have become to be known as a "Trans-

"Tec hnical Director. CQ.

match." This is a title suggested in an articleon a matching device described 'some timeago by Lewis McCoy, WlICpt.

Commercial versions of WlICP 's Trans­match arc produ ced by the James MillenManufacturing Co., Inc. There are twomodels, the No. 9220 I for handling up to300 watts peak r.f. power and the No. 92200for 2 kw peak. Both models are designedto allow a 50 ohm transmitter output on the3.5-28 mc amateur bands to be matchedto impedances ranging from 10 ohms up to300-1300 ohms, depending on the frequencyof operation.

Athough they have been available for sometime and are widely used, we shall take alook at the Millen units at this time for thebenefit of those who may have missed otherpublished data on them or to whom they maynot otherwise be familiar.

CircuitryThe basic circuit is shown at fig. I. It con­

sists of an LC network made op of an induc­tor (L,) in parallel with which is a split-statorvariable capacitor (C,). A single-section vari­able capacitor (Co) is in series with the output

l l\1cCoy. L. G., "The 50-Ohmer Transmatch,"QST, J uly 1961, p. 30.

60 • CO • January, 1969 See page 110 for New Reader Service

line. The inductor is tapped to provide band­switching. Examination of the circui t willreveal that it is similar to a Pi-network, ex­cept for the reversa l of the ground and thehot r.f.-input connections a nd the addi tionof the series output capacitor. C 1 providesthe resistive tuning or impedance conversion.while C:!. tunes out the load reactance .

The input to the network is fed througha reflcctorncter that provides relative for­ward-and reflected power readings. Its pn­mary purpose is to show when the Transmatchis properly tuned to provide a non-reactivelow-impedance input as will be indicated bya minimum or zero reflected-power reading.Forward power readings are subsequentlyuseful fo r adjus ting the transm itter fo r maxi­m um output.

An addi tional fea ture is a smaU loop thatallows an oscilloscope to be coupled to thenetwork for monitoring or measurementpurposes.

ConstructionT he Transmatch made avai lable to us fo r

evaluation was the No. 92200, designed fo r2 kw peak power. It embodies the high­qual ity construction which typ ifies M illengear. Except fo r some comments on specialdetails, the type of compo nents and themethod of construc tion are best visualizedfrom the photograph of the interior view,

Rugged variable capacitors with wide­spaced poli shed-aluminum plates are pro­vided to withstand breakdown at the highvoltages with the high impedances that mightbe encou ntered in the particular portion ofthe circuit under the vario us conditionswithin the design limitations. In the case ofthe parallel capacitor, the breakdown ratingis 6000 volts, while that of the series capaci­tor is 9000 volts. The capacitors are mountedon 1" high ceramic insulators and the capaci­tor control shafts are insulated from thepanel and the operating knob by high-voltagetype ceramic couplings.

The inductor is made up of two sections,both of which are used for 3.5 and 7 meoperation. Only the smaller inductor is usedfor 14, 21 and 28 me. They are space-woundwith # 10 wire held by grooved glasskydsupports. The oscilloscope-coupling loopmounts alongside the smaller inductor section.

The bandswitch is one of the Millen 51 000series, designed especially to handle highr.f. currents and voltages? It has large size

:!"New Components by Millen M fg.." CQ, JuneJ965, p. 55.

See page 110 for New Reader Service

O ' C"IO'COOf

'"•

Fig . I -Setup a s' used in the Millen Transmatch .Details are given in the text ,

heavy-duty solid-silve r contacts and silver­plated conducting eleme nts. A very heavyspring pressure is used to further ensure a lowresistance r. f. contact and reduce heating,while a positive snap-in detent maintains cor­rect alignment.

When the switch is operated . both theswitch contacts and the common connectionto the switch arm arc opened at the sametime. Th is provides a dual break to minimizearcing should a "hot switch" be inadvertentlyattempted. The insulated fr ame is made ofglass-reinforced alkyd that has a very highvoltage-breakdown characteristic and whichis most resistant to arcing and arc-tracking.

Since the 3.5 me band covers a large per­centage of the basic frequency, two band­switch positions are pro vided fo r this rangeto optimize operation toward both the lowand high ends of the band .

The reflectometer is the trough-line type.Its associated meter is a 0-500 microamp joband it is completely shielded at the rear. For­ward- or reflected-power readings arc selectedby a panel switch, while another control ad­justs the meter sensitivi ty.

Dial scales, calibrated 0-100 in uni t steps,are provided for both the parallel- and series­tuning capaci tors. They are useful for loggingthe sett ings for operation on various bandsor under different conditions. Reference tothese settings thus avoids the need for anyextensive retuning, or determination thereof,when changes in operation are made .

The Millen transmatch is built on a heavy­gauge chassis formed in one piece alongwith sturdy side brackets to which the panelis fastened. The cabinet-slides into lips thatare bent around the edges of the panel. Thisproduces a very tight fit which, together withspot welding along the joints of ·the cabinet,results in a virtually water-proof enclosurethat provides the maximum effectiveness o f

January, 1969 • CO • 61

•

Interior view of the M illen 92200 Tronsmatch.The series-luning capacitor is at the left . Thepara llel-tun ing one is 0 '· the right. The h.f. in­ducto r is the sma ll one near the center. Thela rger inductor, toward the bottom of the photo,is added to the h.f . inductor fo r the lowe r fre­q ue ncy ba nds. The ba ndswitch is unde rneaththe round meter sh ield on the ponel a t the top.

the shie ld ing for the minimizat ion of strayr.f. rad iat ion or harmonics that might o ther­wise cause LV.i. or other difficulties. This isfu rther enhanced by the shielding at the rearof the meter. In addition. all the metal workin respect to the above is copper-plated. Type50-239 u.h.f. coax receptacles are furnishedfor the input. output and oscilloscope con­nections.

The size of the No. 92200 2 kw Trans­match is 7" x 14" x 13~ " (h .w.d .) and itweighs 17 pounds. The No. 92201 300 wallmodel is 4 3,4 " x 7" x 9" with a weight of 6pounds. It s smallsize makes this unit suitablefor mobile applications. Both models arcfi nished in medium gray and have blackknobs.

OperationThe No. 92200 Transmateh is designed

to work into a wide range of impedances(unbalanced loads) while providing a 50 ohmimpedance at the input or transmitter end.These ranges a re as follows:

3.5-4.0 mc 10-1300 ohms7.0-7.3 mc 10-1300 ohms

14.0- 14.35 me 10-600 ohms2 1.0-21.45 mc 10-500 ohms

62 • CO • January, 1969

28.0-29 mc 10-300 ohms29.0-29.7 mc 10-700 ohmsPresumably these specifications arc fo r

resistive loads. The maximum values for re­active impedances may differ somewhat.

Operat ion on MARS freq uencies in the 3.0­5.2 mc range also will provide matchingranging from up to 8000 ohms at 4.6 me to90 ohms at 3.0 and 5.2 mc.

Ad jus tme ntDetailed information for adjusting the

Transmatch is given in the instructions sup­plied with the unit. Basically it simply in­volves initially tuning up the transmitter inthe normal manner, setting the Transmatchmeter-sensitivity control for a convenientforward reading near fu ll scale and then.with the meter switched to read reflectedpower. alte rna tely adjusti ng the two T rans­match capacitors until a zero reflected-powerreading is obtai ned.

The instruction sheet also includes chartswith calibration cu rves indicating the capaci­tor setti ngs over the operating-impedancerange fo r the frequencies at the end of eachamateu r ba nd. T hese are helpful as a guidefo r providing approximate dial sett ings fora star ting point before tuneup or for esti­mating the actual load impedance aftertuneup.

It sho uld be noted thaI the T ransmatehis designed fo r operation with unbalanced o rcoaxial line loads. Where the load is abalanecd affa ir. a suitable balun should beused between the transmitter and the load.

Perform nn eeThe Model 92200 Transmateh was tested

using a 2 kw p.e.p. input amplifier with 1300watts output. 0 problems were encoun­tered with voltage breakdown or overheatingand in easily obtaining a 50 ohm match tothe transmitter with a number of differenttype loads. including a random length end­fed antenna working against ground . Oneimportant consideration found in most cases,especi ally in relation to operation with anend-fed antenna. was that the Transrnatchshould be grounded directly rather thanre lying on a ground patch through the shieldof the cable to the transmitter. There is noground post on the unit, but the connectionmay be made to a screw at the rear.

No built-in provisions are included tobypass the network fo r direct feed to the

[Continued Oil page 98 ]

Se e page 110 for New Reade r Service

quency plus 8.895 mc.OPERATION MODE: Fundamental, except 3rd

overtone above 16 mc.TOLERANCE: .01% .HOLDER: HC-6/ U .P IN DIAMETER: .050".PIN SPACING: .486*.LoAD CAPACITANCE (CL) : 32 mmf.INTERNAL CAPACITANCE (Co): 7 mmf max.SERI ES RESISTANCE (Rs): 25 ohms max.DRIVE LEVEL: 10 milliwalts. •

USA-CA [From page 82J

of some 340 U.S. and Canadian Awards andrules. Also explaining AWARD Abbrcvia­tions such as GCR, AOM , AOMB, AOMBIM as well as latest phonetics, etc. The cost­$4.00. send to Amateur Radio AchievementClub. Box 7326 Euclid Stations. St. Peters­burg, Florida 33734.

Some of you will be reading this aroundChristmas Time (1968) and other in Janu­ary (1969). so in view of the fact that inwriting the column 2 months prior to publica­tio n-I showed I was human (?) and failed towish you-A WONDERFUL CHRISTMAS- last month. May I now say, I hope "Santa"brought you a new upgraded license, manyneeded QSLs and some new equipment (andgood health). May I also wish you ALL T HEBEST IN T HE NEW YEAR (1969). Amongyour new resolutions I hope you included o neto be sure to write me and tell me-Howwas your month? 73, Ed.• W2GT. •

Sunspot Story [From page 59J

should also be possible at the same timeduring all but the summer months.

During 1969, an occasional F-2 layer 6meter opening should be possible during thefall, winter and spring months across thecontinent, between the mainland and Hawaii,and between the USA and Central and SouthA merica, and perhaps other areas as well.These openings should occur around noon­time and during the early afternoon hours.T rans-eq uatorial scalter openings generallypeak d uring the evening hours.

In summary. 1969 is also expected to godown as a very good year for h.t. propagationconditions. _

CO Reviews : Millen [From page 62 )

antenna. but although such a setup mightfurnish convenience in some cases, chancesare that such switching would not be re­quired, even with a multi-band antenna

98 • CO • January, 1969

•system using a common feedline, inasm uchas the Transmatch can be used for propermatching on the available bands.

Where bypassing is required or other an­tenna fee dlines need be connected, from ourexperiences wi th other antenna-matchingdevices equipped with internal switch ing, itcan be done with lower loss and less im­pedance discontinui ty by use of a goodexternal coax switch.

A nother feature of the Transmatch is thatit will attenuate harmonics. The seco nd­harmonic attenuation measured on the Millenunit averaged 16 d b, depending o n the fund a­mental frequency and the matching-imped­ance settings used at the time. T he averageloss of power through the netwo rk measured0.5 db.

Although the bandswitch is designed forhigh-power applications. operating it withpower applied is not recommended. especiallysince switching transients or momentary lossof load caused thereby may result in arc-oversor other serious damage in the transmitteramplifier. The heavy spring pressure andsolid detent of the swi tch require q ui te a bitof twisting energy before the swi tch turns.This can serve as a good reminder to cut offthe transmilter power, before the switch isactually rotated.

As a final comment, it should be notedthat the Transmatch does not alter the s.w.r.on the transmission line to the antenna. but itsimply allows the transmiller to look into anon-reactive 50 ohm load Or the equivalentof a I: I s.w.r. on a 50 ohm line.

The Millen No. 92200 Transmatch (2 kwpeak) is priced at $147. T he No. 92201 (300walls peak) is $77. These are products ofJames Millen Mfg., Co., Inc ., 150 ExchangeStreet. Malden, Mass. 02148. •

Contest Calendar [From page 73J

meter Novice band. Operation is also plan­ned on 2 and 6 meters.

A special QSL card has been printed forthe occasion. Send yours to: Colonie CentralH igh School Rad io Club, 100 Hackett A ve.,Albany, New York 12205.

Editor'd NotesConditions for the Phone Contest were

again excellent. especially on the higher fre­quency bands. Looks like George Jacobs hasscored another hit, and Freddie Caposellawill have to rewrite the record book.

The list of claimed scores is only a cross-

See page 110 for New Reader Service