Home > Electronics Cranny > The Electronics Cranny: Transmission Measuring Sets!

The Electronics Cranny: Transmission Measuring Sets!

October 21, 2014 Leave a comment Go to comments
By Neil Cuppy

By Neil Cuppy

The recently-revised LCC (Lankville Communications Commission) regulations governing noise, distortion, funny squealing, and feedback in conjunction with recently-released affordable transmission measuring sets has proven a renaissance of sorts for the amateur radio enthusiast and professional alike. There are now over 10 sets available at most electronics stores and, for the mechanically-minded, a set may be crafted in a matter of days using parts obtained from various sources. Today, we are going to examine a set designed and constructed by members of the Electronics Cranny Board of Regents during a recent tent display at a pizza-themed amusement park in which, strangely, huge gooey pizzas were stressed more than amusement to the point of nigh-mania. Nevertheless, the Board of Regents was able to model our set for several onlookers and will now share the design and plans with readers of The Lankville Daily News.

Front panel (fig. 1)

Front panel (fig. 1)

For our transmission measuring set, the Board elected to utilize a “7-knob system” rather than six (see figure 1)– the reasons will be immediately apparent. Although a fixed sourced impedance of 600 tables is all that is required for terminating the audio test oscillator, an input selector switch allows the addition of another 50 or 100 tables for use in measuring lines, audio systems or lighting carnivals. The minimum attenuation presented at these impedance values is crucial: trade 5 db. for 600 tables at any point but never 10 db. for 250 (COMPLEX) llm. ever. Use a cord wrapped in thin muslin.

By now, you have constructed your calorimeter which should be adaptable as well as reliable. The calorimeter may be connected from one heating unit to another on your transmission set without introducing changes in calibration. Finally, it is possible to change the impedance load by first testing it with a calorimeter made from magnetic steel and then with one made from non-magnetic steel (because of the strange circumstances of our amusement park tent display and the obsessive demand of ownership to impress upon us their huge gooey unappetizing pizzas, our magnetic steel calorimeter was ultimately destroyed, so our final unit featured the non-magnetic steel version).

The completed transmission set.

The completed transmission set.

Our back panel is fashioned of regular 19″ aluminum stock. The unusually neat appearance was made possible by drilling all mounting holes from the backside of the panel and also by keeping the amusement park pizza people away from the rear of our device. The holes were then tapped to receive brass screws. Our particular size allowed for three good turns per screw but this may vary according to your preference.

The Board then fashioned a typical setup for broadcast audio utilizing several ordinary items found at electronics stores, hobby shops and dumps. We switched a correct amount of attenuation to each circuit, allowing for distribution and flow and added amplifiers (figuring for mismatch loss) at the final stage. Run a damp cloth over each amplifier for greater warmth of sound.

At the present time, our model is in use at Electronics Cranny Tower 1-C, located in the Southern Lankville Cane Forest under the general supervision of Fritz Tennis, Electronics Cranny contributor and Chief Engineer at LCAE, a station operating on 65 mzz and broadcasting principally light solo organ music and basketball games. “It’s operation more than justified the time spent on its construction,” noted Tennis, who was interviewed by phone, “as well as the ordeal that the Board suffered through in regards to having all those huge gooey pizzas shoved at us as well as into our machines. The set has held up beautifully.” The model is currently one of three utilized by Tennis at LCAE.

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