GB967018A - Tuner unit - Google Patents

Abstract

967,018. Radio receiving circuits. PYE Ltd. Aug. 8, 1963 [Aug. 11, 1962], No. 30875/62. Heading H3Q. A tuner operating over both V.H.F. and U.H.F. bands-as shown comprising a groundedgrid R.F. stage V1 coupled by means of a tuned bandpass filter to a mixer/oscillator V2-is tuned by means of ganged variable capacitors C1-C4, in conjunction with half-wave lines L2, L3, L4, L6 respectively and trimmer capacitors T1-T8 on the U.H.F. band. In accordance with the invention the coils L8- L9 and 10-15 used on the V.H.F. bands are switched across the trimmer capacitors TC1, TC3, TC5, TC7 at the ends of the lines L2, L3, L4, L6 remote from the ganged variable capacitors C1-C4. In this way these coils are introduced at points which constitute voltage nodes at U.H.F. and so the stray capacitances associated with the switching circuits cause a minimum disturbance of the tuning on the U.H.F. band. The V.H.F. switching is arranged so that in the aerial circuit different coils, e.g. L8, L9 are alternatively switched into circuit for different frequency ranges. In the other circuits the coils for the higher frequencies, e.g. L14, are switched in parallel with the coils, e.g. L15 for the lower frequencies, the switching in each case being by means of a slide switch. To avoid interference from U.H.F. stations when operating on V.H.F., the line L3 is detuned by means of a conductor D.C. which is moved into close proximity to it upon operation of the slide switch. A.G.C. may be applied to the R.F. stage V1 and the arrangement may alternatively be modified so as to use transistors (Fig. 2, not shown).