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Show (KdUad by a. Douglas Wartfrop. Editor of Radio Merchandising ) . ' i ' "I ' JL -a & v&l T it . This Diagram Illustrates How the Double Pole, Double Throw Switch I Em. ployed. Wave Lengths Depend. Upon Position of Switching Device. By FRANCIS H. ARMSTRONG , One of the problems troubling muny radio fans at the present time Is the adjustment of their sets to coyer the higher wave lengths, especially of 492 and 520 meters. One method that may be applied to most receivers In present pres-ent day use, and particularly those of the two variometer and varlocoupler type, Is by the addition of Instruments called condensers. - Where such loading load-ing of capacity Is resorted to great care must be exercised In securing regeneration re-generation over the wave length bands desired. Most receiving sets embodying radio frequency will remain Just as they are. These Instruments are governed by the range of transformers Included In the construction of the set, and the general practice of most manufacturers manufac-turers has been to design their radio frequency transformers to cover a wave length range of from 800 to 550 meters. There Is no question regarding regard-ing tuost of the transformers made today, as the majority run as high as the new wave length of 526 meters. In some cases where a loop aerial Is employed In conjunction with a rndlo frequency set more turns of wire on the loop may have to be added In order or-der to secure sufficient added Inductance Induc-tance In this part of the circuit to reach the wave desired. The reason for this Is that the loop acts In this case as a tuning hmuctnnce. Should the loop aerial be deficient In Its inductance in-ductance value, then there Is no resident resi-dent point to work on for the higher wave lengths. Better service may be of mica and copper foil machine pressed or firmly clamped... Load Circuit Carefully. Where-loading Is resorted to great care must be exercised to procure regeneration re-generation ob the higher wave bands. A double pole double throw switch Is shown In Figure 1. When the position po-sition of the switch Is such that it neither cuts In or out condensers the set is standard and will operate nor ftially over Its limit of wave length range. Should the condenser switch be thrown to a position Indicated for Ihe "000-meter" stations, then two condensers In series are cut into the circuit and placed across the grid variometer vari-ometer and secondary of coupler. The switch thrown to the position of "1,000 meters" has a different effect. ef-fect. It disconnects all previous con nectlons and adds capacity from the plate circuit to the grid circuit. The two condensers are connected In series, the connection being made from the plate back to the filament. Another connection Is then taken from the center of both condensers and placed to a point Just prior to the grid condenser, but In the grid circuit This then provides for capacltatlve regeneration re-generation over the entire wave length range up to 1,000 meters. The condenser values should average aver-age about .00025 capacity, and, as explained, ex-plained, should be of the mica and copper foil type. Why most of the sets failed to function properly Is due to the fact that regeneration was not available on the higher wave bands. In Figure 2 a cam switch or antl- .tmnrltv tvttnh Bmniraman. la lljua- trated, but this Is merely a method of accomplishing the same result as the previously mentioned switch. The appearance and arrangement of the cam switch appeals to most radio funs, and therefore Is more often employed. The amateur who Is willing to "make i his own" must bear In mind that foi proper results regeneration Is essential essen-tial on the higher wave bands. Ne York Sun. uuu u lilt: unguiui iihij lO BUIJIUCIJ with a sufficient number of turns on Its frame, which are then varied by means of a suitable tapping or a switching arrangement. Leading Three-Circuit Tuner. Under this type ! of regenerator comes the well-known two variometer and varicoupler circuit. This type of apparatus has become the prize receiver re-ceiver of many a radio fan, since it contains the elements which give a set selectivity, but since some new stations were Injected Into the ether It seems that most of the variometer sets fall short of bringing In concerts con-certs oa the longer waves. With this set an arrnngement can be mude to secure se-cure shorter waves with their maximum maxi-mum signal strength Just as efficiently efficient-ly as when using the longer wave length bands. This arrangement consists of employing em-ploying a double pole, double throw switch, or by the use of an antlca-pacity antlca-pacity switch. The first arrangement would be the better of the two for the beginner or novice, since It appears ap-pears to be much simpler. In the accompanying ac-companying diagram (Figure 1) one may get an Idea how the double pole, double throw switching arrangement Is employed. The wave lengths depend de-pend entirely upon the position of the switching device. In Figures 1 and 2 the condensers are represented by C. These condensers con-densers may he made at home or they can be purchased at any radio shop at the option of the builder. If purchased pur-chased the fixed type coudenser Is to be preferred. In shopping around the fun will run Into vnrlous types of fixed condensers, many of them consisting con-sisting of paper and tinfoil. This type of condenser should not be considered, as Its capacity Is not uniform. In recent tests some of these paper pa-per condensers gave no fixed reading whatsoever; capacities vurled any-where any-where from .0002 to .001 mfd. merely by pressing the condenser together with the fingers. Due to their loose construction, moisture creeps In and varies the capacity to the same degree de-gree of liiHmiriicy. What the fan should buy Is a condenser constructed 1 T HiM n FG2 I j Cam Switch or Ant! Capacity Switch Arrangement l Merely a Method of A a i compiishmfl Same Result as Double ! hrow Srvitch. |
