AM reciever with MK484
Posted on Oct 31, 2012 8292
The basic MK484 (Replacement for the ZN414) connected in its minimum configuration as a radio receiver for the A.M. Broadcast band and the upper half of the United States' FCC Part 15 Lowfer (1600-1750 meter) band. Its a circuit straight out of the application note and I have fount it to be useful on the bench. Even more convenient that using the Radio Shack short wave receiver, mainly because the tuning is so broad on this that I don't have to tune precisely to hear the signal.
I put this together to evaluate the MK-484 as a possible remote control/data receiver for the 1600-1750 meter band. The on-off switch is hardly necessary because of the low current draw of the circuit, but one never knows if one is going to add more circuitry later. When listening to the AM (MW) band, there is a lot of EMI to be heard, but went it is switched to the longwave band (LW), the EMI disappears. This agrees with the datasheet showing sensitivity dropping off quite a bit a the LW frequencies compared to the MW frequencies. This chip would certainly be a nice receiver or IF around 1 MHz but seems to come up short in the sensitivity departmentat 180 kHz. Still, it might come in handy for some very short range applications. The cutoff frequency of the output RC is 1.6 kHz. I tested the receiver with the 187 Khz RF Source also mentioned on this site. Indeed, checking out the MK-484 was the first use of the 187 khZ RF Source. I had acquired the radio parts - the ferrite coil, tuning cap, and the KM-484 from Peter Crowcroft's Kitsrus.com web site on the component sales page (http://www.kitsrus.com/bits.html). As for the high impedance earphone, I found that in Bahnmo Plaza, and electronic components market in Bangkok. You are on your own as far as finding one elsewhere.This expression is approximately correct at room temperature, and the gain varies directly with absolute temperature, assuming the collector...