Dick Smith Electronics Uhf Wattmeter

I'm gomg out on a limb and pred<cl that one of me best things to happen to electronics in the US this year is the emergence ol Dick Smith Electronics. Incthe California-based arm of Dick Smith Elec-ironies Ply Ltd. ol Australia. Tnis unjque io^pany offers a full line of electronic parts, kits, and pre wired assembles us-jng a marketing and advertising style that is sort of a cross between the old PoJy Pakg catalogs and Radio Shack.

According to their sales literature, the company has been In existence since 1966. when Dick Smith started his own tway-radio service business Today. It is a mult million-doliar retail operation, but in typical fashion we here the (JS have heard little or nothing about the company. HoweverT that will change—very soon!

Among ihe many items That DSE carries <n their product iine are kits ot alt sortstest equipment, e*perimenier s kits, audio amplifier k ts, and even a lire ol .ntroduc tory kits called "Fun Way into Electronics. " which is apparently quite a Ml "downunda (that is. Australia). The devef opmeni team at DSF apparently scours ihe amateur publications in VK land looking for new ideas as well, which brings me io this particular review item- -ihe model K-6312 UHF jvattmetef kit which features 10- and 50-Watt ranges

Shortly aher the kit was received here, j call came Jn from Ike Bam. the President of DSE, informing me that I had been shipped the wrong meter movement for this kit He ihoughr i had been sent ¿i 100--mi hamper« movement wi^en In reality 't was a t-mil Hamper* nwvofflent Regard

Dick Smith Electronics Australia Kit
ing. The displayed power comparisons -vert as follows:

Trie Dich Smith Electronics mooef KS312 UHF wattmeter

¡ess. a promise was made to forward a lOD-microampere movement and I set about building the kit

Dick Smith provides a considerable amount of information with this kit. A Jong article discussing swr (standing-wave ratio! from Electronics Australia's November. 13B4, issue is reprinted as pan of the assembly instructions, presumably to give the builder a better ideii ol what nersfte is actually measuring. This is followed by a short article describing the theory and op oration of the wattmeter kit, and then the .assembly instructions. A parti list and schematic round out the printed materials. (A supplemental bolder describes Ihe basics of kit building for the inexperienced.)

This wattmeter is very similar to the type I wrote about in the September. 1984, Issue of 73 c'Eiemontary, My Dear: Watts n' Swrh ). li uses a stripline transmission ime {nominally 50 Ohms) with a pair of coupling imes running parallel to it on either side of the PC board. Tne one vari»-tton from the earlier 73 circuit is another piece of PC hoard laid across the top ot the stnplme to act as a shjeid (similar to a piece of coaxial iransmlsslon line), Hewlett-Packard 2&0G not carrier diodes detect the forward and reflected voltages, which are fed 1o several v-^pots to &et the »detecting ranges. A 100-microampere meter is used to d(spla> ihe forward and re fleeted values.

Kit assembly is not complicated and even the most cautious worker can put this together In three hours AH parts are seated in plastic and there are generous amounts of extra hardware and solder pins tor making connections to ine PC board However, me original meter thai shipped hac: its face neid on with sticky lape and the mounting screws were nowhere lo be found! This complicated matters when J tried to fit the custom DSE wattmeter scale to the original i milliard pere meter, and I had to resort to using a thin coat of rubber cement io hold it in place. The subsequent arriva1 of the correct meter solved the problem, as it had the correct screws with It.

Another tricky aspect of this project is the assembly in and around the enclosure.

which is basically a one-piece box a th the 3tdes open. These sides are closed with two panels when the profect is complete. The final result looks sharp but it makes For a lew wiring headaches during assembly. Once me si spline assembly is complete ft is then fastened to a tinned shield plate and attacned to rwo BNC-type connectors on ihe rear panel The top shield PC board js ihen fastened with two nylon screws. At this point, you are ad vised to solder the edges ol the stripline board to ihe tinned shield plate through the meter hole In the box. This Is quite tricky it you want to get a good soldered edge an tne way around tne o:<ard

I aouic suggest using a chisel tip for your Iron !o do this |Ob since there isn't a lot of room to maneuver around Also, you have to Install the front-panel switches and then solder their associated PC boards to their terminals to make sure Ihey line up correctly. This ts detailed m :r>e instructions. FmaHy. securing the me ter itself to the fr?ni panel requ defcie* ity with a socket from a drive set. since the clearance will not allow for a drive handle. Using pliers to Lighten these small nuts is cheating and won't provide th«1 secure iii necessary!

To summarize construction: The assem bly manual ?s straightforward but Ihe technique is jnus^a It c.jn accomplished by the novice builder although having small agik fingers helps in a few cases

Now to the nitty gritty. How well does it work? A lest setup was made using a short piece of Bel den 8214 Ironi a Microwave Modules 432-2&S transverter This in turn led the DSE wattmeter and ther using adapters, a Bird Model 43 coupler was attached lo the output of the DSE wattmeter and terminated In a Biro Termaiine 50-Watt coaxial resistor. The MMM32-28S normally puts oui to Watts when driven by a Kenwood T&430S

Boin lorward ano ^fleeted ranges were calibrated agamst tne Bird To ensure the highesi .iccurac*. calibrations were maao at mid scale on both meters (i.e., 5 Wattsi Additionally, measurements were mad*1 with the Bird before the DSE wattmeter to verify Its claimed 50-0hm impedance rat-

WHAT DO YOU THINK?

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OSE UHF Wattmeter fWitts)

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