LED tuning indicator - illuminated tuning aid

This LED field strength meter can be connected to FM receivers in which the CA3189E IC is used in the IF stage. An example is the FM, IF stage described in the July/August 1979 issue of Elektor. A bar display is con- structed with a UAA180 and 12 LEDs. Preset P1 sets the sensitivity of the circuit. The voltage across P1 is stabilised to 5-6 V by R1 and D13. The input to the UAA180 is connec- ted to pin 13 of the CA3189E. The relationship between the operational and the input voltage is clearly shown in the form of a graph with the vertical axis graduated in volts and the horizontal in micro-volts. A logarithmic progression is clearly illustrated. P1 is adjusted so that at the strongest transmitted signal all the LEDs are just lighting. The circuit can also be used with other IF stages, but, then there may be a problem in calibration. Luckily most commercially made FM receivers already have a strength indication of some kind, which will show not only where to connect the input, but, wil