RF Cafe Software
About RF Cafe
1996 - 2022
BSEE - KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ...
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January 1935 Short Wave Craft[Table of Contents]
People old and young enjoy waxing nostalgic about and learning some of the history of early electronics. Short Wave Craft was published from 1930 through 1936. All copyrights are hereby acknowledged. See all articles from Short Wave Craft.
Even with all of today's prefabricated components, gizmos, and tools - at incredibly cheap prices - there are still many people who prefer to make their own non-standard parts and even tooling when tinkering on a project. Many hobby magazines have monthly columns dedicated to hints, tips, shortcuts, ideas, etc. to solve, remedy, conquer, etc., the many kinks, problems, challenges, twists, hitches, snags, etc. of the task at hand. The aforementioned words can be found in the titles of those columns. Short Wave Craft magazine ran a feature titled "$5.00 for Best Short Wave Kink" that rewarded readers for submitting nifty ideas. Contemporary magazines and websites still offer cash rewards, typically in the $25-$50 range.
Simple Antenna Coupler
Here is a description of a home-made antenna coupler that can be used in conjunction with any of the four prong plug-in coils. Two pieces of hard rubber were cut from an old panel and drilled as shown in the accompanying drawing. (Fig. 1). The primary coil consists of ten turns No. 24 D.S.C. copper wire, wound on a form of approximately two and one eighth inches. Paper is first wrapped several times around a two inch form and the end pasted. The wire is then wound over this, the turns being kept close together, and glued in several places. Small strips of paper are then glued on the outside of the coil and left to dry. The coil is then removed from the form and the strips of paper are then fastened around the turns, making a firm, self-supporting coil. The coil is fastened to the little rubber strip by inserting it into the saw cut at one end and glued. (Fig. 2) - Ernest Dummer
This map will be most convenient to a Short Wave DX'er. I am very much satisfied with this map.
It is made out of an old blind, set up the blind and glue your map to it. When not in use zip-up. This is welcome where space is limited. - John Vetter.
Here is a description of an improved grid cap connector made out of spring curtain rods. A spring can be obtained at any five and 10 cent store. Cut a piece of spring about one and one half inch long, put the ends together and put a drop of solder on to hold the ends tight together. Then solder a piece of wire on for the connection. Then place the completed cap over the grid connection of the tube as shown. - Ervin Sperath.
After having so much trouble with the wire on my set of headphones, always continually twisting, I hit upon the idea of twisting push back wire around the two wires from phone to plug in cable. It solved the situation completely as it keeps the wires in the most convenient place. Joel Levy, Jr.
Many times I have desired to make use of a public address system at parties, etc., and finally hit upon the idea of constructing a 245 oscillator which can be connected directly to the broadcast receiver. The oscillator is modulated with an ordinary microphone in series with the B negative supply. By tuning the oscillator and broadcast receiver to resonance the oscillator acts as a miniature broadcasting station and full speaker volume can be obtained. However, care should be taken to make sure that this instrument does not interfere with other receivers in the neighborhood. - Marine Schell.
Short Wave condensers are quite expensive and having some old 00035 on hand I thought of separating the stator plates in half and making two small condensers which would be ganged together. and varied by the same rotor.
Taking the condenser in half, with the center plate removed and four plates on each side, the condensers will have a capacity of about 0.00016 mf. each.
The old condenser is taken apart or rather the stator is removed, the sides cut through at the middle plate which is removed, and the inside ends filed smooth. A metal plate is cut out to fit in between. And when the stators are assembled back this plate is inserted between the stators with rubber insulators holding it in place tightly. It is then grounded thus shielding the two condensers.
I have used this condenser in the two tube super-het in your December issue and have obtained fine results. Diagram appears above in next column. - E. M. Granville.
Here is drawing of a dependable switch mount. This is made from an old discarded metal cased earphone. You just have to drill a hole in the middle and mount the switch. Then lead the wires from the switch out of a hole drilled in the side.
This is very handy for "bread-board" transmitters and receivers and in dark places where it is hard to find small toggle switches. It is a good idea to have a large washer when you mount the earphone cap, so as to take the strain off the bakelite. - Joe Bergsieker.
A very efficient stand-off insulator can be constructed from a 5 inch porcelain insulating tube. Both ends of the tube are fitted with wood dowels in order to facilitate mounting. The drawing below clearly shows how the screw is fastened in one end and how the base is fitted to the other end. - George Shenberger.
Handy Substitute (no drawing)
For the "Ham" who gets all set to test his Transmitter some evening and finds that his neon test bulb has been lost, stepped on, or the baby has swallowed it.
Dig down in the junk box and salvage an old Raytheon Rectifier tube, type BH, connect the four prongs with a piece of bare wire and you have as serviceable test bulb as you had before, giving a glow much the same as your neon bulb. - Marine Schell.
The above diagram clearly shows the construction of an instrument which can be used for cutting large holes in bakelite or metal panels. The drawing clearly indicates how simply this tool can be constructed. The cutting instrument should be made of high grade steel especially where hard materials are being worked. The 3/4 inch square block can be made of ordinary iron. The drawing below shows a very simple method of constructing a punch for making socket holes in metal panels or chassis. Secure a piece of' 1 5/16 inch outside diameter pipe, file each end as straight as possible and sharpen one end in order that a cutting edge will be effected. Simply place the panel to be punched over some hard wooden material. - S. B. Wells
By using two tube bases as shown in the diagram you can increase the length of the coil in order to accommodate the larger windings. This is done by sawing off the prong end of one tube base. Then put the two coils end to end and wrapping them with glued paper - R. S. Dekker.
Cheap Lead-In (no drawing)
I think that a pair of lead-in bowls made from two coffee pot tops is the cheapest that any "Ham" can get. Drill a hole in each top and through the pane of glass, then put one on each side of the window pane with a 6"x 1/4" brass bolt with a washer and nut on each end of the tops - Harry Gaul.
Posted February 8, 2017