OM MICRO RECEIVER TUNING DIODE VARICAP
SCHEMA OM MICRO RECEIVER TUNING DIODE VARICAP:
This is a great receiver for the range of Medium Wave (500 - 1700 KHz) which is obtained by tuning the potentiometer PI, exploiting the characteristic of the diode DV1.
WARNING!
If using a stereo headset 2 x 32 Ohms, a bridge is realized between the points X. If you use a high standard 8 Ohm speaker, resistor R4 (56 Ohms) is inserted between the points X i1 must be very attentive during the construction of the coil LI to be 60 turns of copper wire enamelled wound on the ferrite bar. The turns must be disposers side by side. It is advisable to start the coil construction by setting the first turn with glue quick setting (cyanoacrylate), then continuing and securing the denier turn with the same type of glue. The coil should be fixed, also with glue a fast setting on the circuit printed respecting a minimum distance of 10 mm between the circuit and the integrated coil. The ends of the terminals will be scraped to remove (email, aulrement it will not be possible to lessoudcrau Circuit prints. For good listening with speaker, the HS 235 can be torque to the HS 140 or another BF amplifier A piece wire a few meters, which serves as an antenna, can be applied at point A. This precaution is generally not necessary thanks to its high sensitivity. The supply voltage must be that of a simple battery 9 V the maximum consumption is 18 mA only.
HOW T'lL:
The emitted AM signals in the range of medium waves are received by the coil LI and PI selected by the potentiometer, the latter role is to apply at the ends of the varactor DV1 according to a specified voltage receiving station. Given that DV1 is a varieap diode, its internal capacity varies with reverse voltage applied, so when the tension is to zero, the capacity is maximum and when the voltage is maximum capacity is the minimum. This amplitude voltage (and therefore of capacity), determined by the potentiometer PI allows the receiver to tune in a range of frequencies between 500 and 1700 KHz. It should be noted that the diode DV1 varieap through C6 and C8 capacitors, is almost in parallel to the coil LI. Zener diode DZ1 provides good voltage stability for control of varieap diode and therefore the responsibility of the syntonic tuning LC group (coil and diode varieap) is represented by the 1'entree system that integrates, thanks to its very high impedance, ensures that Q (quality factor) is high enough canned ensuring good selectivity. The signal then passes through at least three stages of high frequency amplification; Finally. Mid owner detector extracts the signal transistor Low Frequency filter is then applied to the base of a transistor to be amplified.The capacitors C4 and C5 are designed to obtain the maximum discharge of network perturbation signal at 50 Hz. The latter represents the transistor in the circuit structure integrated, whose base is connected to the collector direclement BF amplifier transistor, a a role of impedance adapter of way to ensure a discrete current in the d * listening transducer which should have a 64 ohm impedance is SUPERIOR. That is why when using a headphone 8 Ohms, place in the latter series has a 56 Ohms resistance (56 + 8 = 64). Supply voltage integrated circuit (pins 4 and 6) must be stabilized and DO NOT EXCEED 1.6 Volts. This function is performed by silicon diodes Dl and D2 connected in series and inserted in direct conduction.Their threshold voltage being 700 mV, voltage to their ends (pins 4 and 6 of IC1) can not be superior about 1.4 volts.
LIST OF ELECTRONIC COMPONENTS:
All resistors are 1/4 watt unless otherwise noted. R = 100 Ohms R2 = 1 Kohm R3 = 150 Kohms R4 = 560hms PI = 100 Kohm A. CI = 100 nF ceramic. C2 = 100 nF ceramic . C3 = 100 nF ceramic. C4 = 100 nF ceramic. C5 = 100 nF ceramic. C6 = 10 nF ceramic. C7 = 10 nF ceramic. C8 = 47 nF ceramic. C9 = 180 pF ceramic. Dl = 1N4148 D2 = 1N4148 DVl = BB112Varicap. DZ1 = 7.5 volt zener. IC1 = ZN415E PST = stereo jack socket. lFerrite8X50mm. 1 Support 8-pin.