During the tuning of the receiver to some station at the SW band with the variable capacitor, a problem occurs. In simple terms, the station frequencies are too close to each other, so the capacitor’s shaft should be turned for an extremely small angle in order to change station, which is practically impossible. It would certainly be useful if we could somehow stretch (a popular term for this) the part of the band near the frequency to which the receiver is tuned at. For the direct type (TRF) receivers that were described in the previous chapters, this can be accomplished if, acc. to pic.5.12, another variablecapacitor (CR) is added in parallel to the variable capacitor at the input circuit. Its capacitance should vary at substantially smaller scale than that of C, meaning from a few pF til about 20 pF. The tuning is accomplished by setting the receiver, by means of C, approx. at the middle of the band we are interested in, then tuning by means of CR to some station in that area. E.g. if the stations we want to receive are located in the part of the SW band from 6.1 MHz till 6.2 MHz (it’s a well-known 49-metre band), first we tune ourselves with C to approx. 6.15 MHz, and then we pick with CR some of the stations located in that area. The same applies for the famous Magic Band (at about 50 MHz).The CR capacitor is mounted close to C in order for their knobs to be near each other at the front plate.* As CR, some air-type trimmer capacitor can be utilized, with adjustment knob mounted on its shaft. Also, one of the sections of the variable capacitor from pic.3.8 can be used, as shown on the right part of pic.5.12.* The problem of the station “adjacency” at the SW band also exists at the superheterodyne receivers. It is being solved by adding the CR in parallel to the variable capacitor in the local oscillator circuit. The reason for this is that, at supereterodynes, the station is chosen over the local oscillator. The important thing for the oscillator is to have the exact frequency, that is greater from the station frequency for the amount of the interfrequency. If the resonance frequency of the input circuit isn’t equal to the station frequency, it won’t significantly affect the reception. Because of all this, in the receiver on pic.4.5, CR is attached between the pins 2 and 3 of the LO circuit.