cq amateur radio noviembre 2014
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drawing show where scores are madein the metal, marking where bends willbe made to produce the finished hous-ing shown in Photo A . Using an awl andstraight edge, lines are etched in thealuminum in five increments.
Photo E: Your Metal ShopBending Machine
With these types of projects, Im oftenasked if theres some fancy metal-work-ing shop behind them. Nope. The
bending machine here consists of acouple pieces of flat aluminum stockclamped in a vise.
Line up the score lines correlatingto the red-line measurements in Figure1 with the edges of the flat stock,clamp it, tighten it all in a vise and youreready to bend.
Photo F: Bend, Baby, Bend!As our picture shows, it doesnt take
much pressure to bend this thin alu-minum. Just a finger or two will do. Startwith panel A , the back plane of thehousing. Make sure youve made agood 90-degree bend to form what willbe the vertical section. Its shown in theSIDE VIEW of Figure 1 .
Photo G: Executing The FoldSince we are dealing with one piece of
metal, its necessary to fold the alu-minum to make the second vertical plane panels C and D as we make bendsmoving progressively toward the front ofthe housing. Youll be turning the thinaluminum in different orientations as youget to this point. Dont be discouraged ifyou cant quite visualize a step. Stop,take a minute to think about it and thebending scheme will come to you.
As you can see, it is not necessary tobring the panel C and D verticals tight-ly down on one another at this point. Allyou need is the general shape by com-pleting their bending into a general con-figuration with your fingers.
Photo H: The Big SqueezeOK, now put the U-shaped C and D
panels shown in Photo G between thebending bars. In the vise, tighten themwith all your might.
Photo I. Finishing Up OurBender
Making two more bends completes thegeneral configuration of the housing, asshown in Figure 1 . Note that the verticalfront panel in this picture is much tallerthan that shown in Photo A . Thatsbecause in the second slug-tuned coilthe front panel panel E in Figure 1 was extended to leave the option ofmounting the slug-tuned coil on the frontpanel of the receiver in mind.
Photo J: Drill, Baby, Drill!Beginning with the back of the hous-
ing panel A in Figure 1 drillmounting holes for the coil inductor.Start with a small drill bit and make thehole progressively larger. Grommetsfrom RadioShackfi were used as a
Photo G. 3INCETHEHOUSINGISMADEOFONECONTINUOUSLENGTHOFALUMINUMAhFOLDvISNEEDEDTOMAKETHECENTERVERTICALPLANE
Photo H. 4IGHTLYCLAMPINGTHEhFOLDvOFPANELS#AND$BETWEENTHEMETALBARSANDAVISEBRINGSTHETWOVERTICALPLANESINTOONE
Photo I. 6OILA(ERESWHATTHEHOUSINGFORTHESECONDVERSIONBUILTAT+)3.LOOKEDLIKE
Photo J. .EXTINTHEPROCESSISDRILLINGHOLESTOMOUNTTHECOIL3TARTONTHEBACKPANEL!9OUMIGHTWANTTOUSEAHANDDRILLFORTHESMALLERHOLESINPLACEOFAPOWERDRILL
Photo K. 9OURGOALISTOHAVEEACHHOLEONTHEVERTICALPANELSNICELYALIGNEDFORSMOOTHANDMECHANICALLYSTABLESLUGADJUSTMENT
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cushion between the sheet aluminum and the McDonald'sstraw . The holes are drilled toaccommodate mounting the grommets. The Mac straw fitsthrough their centers with just the right amount of snugness.
Photo K: Assuring Perfect AlignmentWhen the hole on panel A is the diameter of your awl or,
say, a pencil, mark panel C by sighting the alignment point.
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Clamping the housing to the bench and adjusting the awl orpencil to perfectly vertical from all angles will assure that theback-panel hole aligns with the middle-panel hole drilledthrough panels C and D in Figure 1. Note that panel F isbent out of the way to allow marking and drilling panels Cand D. The metal has a way of remem-bering its previous position. Simply bend panel F back to itsvertical position by hand no bending bars needed.
Photo L: Work Slowly and DeliberatelyThis picture shows the beginning of the process of making
the hole in panels C and D to mount the coil. Yes, panel Fis still bent out of the way necessarily. A hand drill wasused to make the small holes, with the electric drill comingin when the diameters were enlarged. The unit is held firmlybetween the flat-stock bars and vise.
Photo M: Our Ducks, and Holes, in a RowAfter making the proper diameters in panels A and C/D to
hold the grommets, panel F is re-bent to vertical. Now usethe same procedure described in Photo K to align the screw-hole needed for on panel F. When all is done, look throughthe finished housing to see the openings match up nicely.
Photo N: Lets Focus on the Lil SluggerAs you can imagine, mechanical stability is often paramount
for slug-tuned coils, especially those used in an RF oscilla-tor. Thats just the case in the receiver design being dupli-cated. So, we must assure the adjustable slug and coil aresolidly in place in the housing.
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No. 6-32 brass nuts are soldered to two small pieces ofprinted circuit (PC) board material to stabilize the metal screwthat moves the slug through the center of the coil.
The PC pieces measure 1/2 by 7/8 inches and are boltedto the front and backside of panel F in Figure 1. Thesetwo nuts keep the adjustment screw from wiggling. NOTE:
Photo O: Time to Get Even More ScrewyTo make a knob for the adjustment screw it was necessary
to cut off the rounded head of a 2-inch long No. 6-32 zincbolt found at The Home Depot. Before doing that, though,a small-diameter hole is drilled about 1/4-inch deep into a pieceof cut-off shaft from a potentiometer. The bolt is self-tappedinto the shaft as perfectly straight as you can make it.
Wood doweling will do just as well in place of the poten-tiometer shaft. Just be sure to glue it securely to the metalbolt.
Photo P: The Pieces are Coming Together!By cutting off the excess potentiometer shaft to leave about
3/8 inch, the majority of the metal work is done. A washer,two nuts, and two lock-washers make the knob.
Photo Q: Testing the MechanicsAs you can see, the PC-stabilizing pieces have been bolt-
ed into place on the front and backside of panel F and thescrew shaft has been passed through panel A to the front ofthe slug-tuned coil housing. The grommets are in place, aswell. At this point we want to assure the screw passes throughthe holes cleanly and that the washer-knob turns smoothly.
Photos R, S and T: Back to McDonald s for aCoil to Go
The procedure for winding the slug-tuned coil begins bypiercing the Big Mac soda straw with a sewing needle, PhotoR. This is where you begin winding with, in this case, No. 26enameled wire. A simple overhand knot will keep the wirefrom pulling through the two holes, Photo S.
When youve reached the required number of turns (for ourcoil, 36) pierce the straw again with the sewing needle andtie-off the wire, Photo T.
Photo U: Slugging Right AlongNow that we know how long the coil is, the Subway straw
can be glued to the screw assembly shaft and cut to assurethe No. 2 core material fully covers the length of the coil. Inother words, the screw assembly can adjust the slug to bebeneath turn of the wire winding.
At the same time, assure that when fully adjusted the otherway twisting the screw assembly out the backof the coil the slug is fully from the inductor.
A small piece of wood doweling is used to plug the backend of the slug, again from The Home Depot.
A Post-It note rolled upon itself worked nicely as a mini-funnel to pour the pulverized No. 2 slug material into theSubway straw. The chopstick was once again called to dutyto tamp and compact the core material before gluing the smalldowel plug in place.
Photos V and W: Final TouchesOnce everything is together, two small pieces of PC board
material are glued to the housing as solder points connect-ing the slug-tuned coil to the rest of the circuit. Photo V iswhat the slug-tuned coil looks like when the slug is fully in.Photo W is what it looks like when the slug if fully out.
Parting ThoughtsThis may seem like an awful lot of work to make a pretty
simple inductor. But if in the end it saves a circuit you haveyour heart set on building, Know, too, youll have thesatisfaction of knowing you cleverly worked around a seriousproblem and Many builders will tell you thatit doesnt get any better than that!
If you take a stab at making a slug-tuned coil from scratch,please let me know how it turns out. And send a picture. Wedbe glad so share it with everyone aboard the train. Write.
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TThere are all kinds of awards a brass pounder canearn regardless of whether the operator is a CWrookie operating an Ameco plastic base, model K-1 key at 5 p.m., or a grizzled veteran smoking CWat 45 w.p.m. with a classic Vibroplex Blue Racer.
CW contacts in all 50 states or all IARUzones
CW DX contacts with at least 25, 50, or100 different countries
CW contacts with operators in each of theinhabited continents
Contacts with all the Canadian provinces
For the very patient and very persistent, there areawards for making CW contacts in every county inthe U.S. And then there are awards in va