crisp@uncecs.edu (Russ Crisp) (03/12/91)
Hello again fellow networkers. I have 2 simple questions I hope someone can help me with. The first, how do you read and understand the values printed on small valued ceramic disc capacitors? There seems to be a pattern on some I've seen. For instance, 103 means .01uF, and 104 means .1uF - I think-. This pattern doesn't seem to hold on other values. Anybody got a clue? Secondly, why is the rf in a radio receiver mixed with a local oscillator to provide an IF? Why not go straight through with the carrier frequency? What advantage does this IF signal provide? Thanks. I appreciate all your responses. Russ Crisp Western Carolina University Cullowhee, NC
henry@zoo.toronto.edu (Henry Spencer) (03/12/91)
In article <1991Mar11.181039.22769@uncecs.edu> crisp@uncecs.edu (Russ Crisp) writes: >The first, how do you read and understand the values printed on >small valued ceramic disc capacitors? There seems to be a >pattern on some I've seen. For instance, 103 means .01uF, >and 104 means .1uF ... Read them as if they were the resistor color code. 123 means 12 x 10^3, where the basic unit is always picofarads. -- "But this *is* the simplified version | Henry Spencer @ U of Toronto Zoology for the general public." -S. Harris | henry@zoo.toronto.edu utzoo!henry
whinery@hale.ifa.hawaii.edu (Alan Whinery) (03/13/91)
In article <1991Mar11.181039.22769@uncecs.edu> crisp@uncecs.edu (Russ Crisp) writes: > >Secondly, why is the rf in a radio receiver mixed with a >local oscillator to provide an IF? Why not go straight >through with the carrier frequency? What advantage does >this IF signal provide? If you wanted to have much tuning range in a radio with no IF, you'd be faced with the formidable task of tuning a chain of filters, which are necessary to achieve selectivity, simultaneously. If it doesn't sound formidable then consider that the tuning element would have to be linear across a wide range of frequency, regardless of temperature changes, parasistic capacitance and inductance, etc. If you "beat" the incoming RF against a Local Oscilllator frequency, thus producing the IF, all you have to tune is the LO. The RF amps ahead of the mixer (beater, whatever) are wide band, the IF filters are all tuned to 1 frequency (usually 455 khz or 10.7 Mhz) and they stay that way. It also makes the detection easier, because the detector in an FM receiver, say, can be built to operate at 10.7 Mhz instead of at 88-108 Mhz, which would complicate the design considerably, not to mention making it more expensive. Alan whinery@hale.ifa.hawaii.edu -- Regards, Alan Whinery whinery@hale.ifa.hawaii.edu