The receiving frequency can be set with a LC tank or with a crystal. To increase the sensitivity of this circuit I have added a antenna preamplifier. All contribution to this page are most welcome! Background I need a simple solution for receiving narrow band FM signals. I wanted to build a receiver wich can handle all kinds of signals.
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These devices are designed for use in FM dual conversion communication equipment. The MC is designed for the use of parallel LC components, while the MC is designed for use with either a kHz ceramic discriminator, or parallel LC components. These devices also require fewer external parts than earlier products.
The MC and MC are available in dual—in—line and surface mount packaging. Input Limiting Voltage Sensitivity of —3. Devices should not be operated at these values. ESD data available upon request. Motorola, Inc. F Mute k 0. F 0. A 70 60 50 40 30 20 Figure 4. Typical level is mVpp. Typical signal level is mVpp. Note that the signal is somewhat distorted compared to that on Pin 1. Riding on the kHz is the RF carrier component.
The typical level is approximately 60 mVpp. A Supply Voltage —2. VCC is decoupled to ground. The signal is attenuated by the filter. The typical level is approximately 50 mVpp. External 0. F capacitors connected to VCC. Composite not yet demodulated kHz IF signal is present.
The typical level is mVpp. This is a composite FM demodulated output having signal and carrier component. The typical level is 1. Waveform VCC 9 ? The typical signal level is mVpp. See discussion in application text. The chip sources up to 60? A over the linear 60 dB range. This pin may be used many ways, such as: AGC, meter drive and carrier triggered squelch circuit.
Waveform Bias 13 40 k 15 Gnd Gnd 15 Ground. The ground area should be continuous and unbroken. In a two— sided layout, the component side has the ground plane. In a one—sided layout, the ground plane fills around the traces on the circuit side of the board and is not interrupted. A 53 k IF Decoupling. A ? Signal level is typically mVpp. A 9 RA Recovered Audio. This is a composite FM demodulated output having signal and carrier components. A Figure The MC and MC are different in the limiter and quadrature detector circuits.
The MC has a 1. Thus, in the MC, no external components are necessary to match the kHz ceramic filter, while in the MC, external 1. The damping resistor determines the peak separation of the detector and is somewhat critical.
As the resistor is decreased, the separation and the bandwidth is increased but the recovered audio is decreased. Receiver sensitivity is dependent on the value of this resistor and the bandwidth of the kHz ceramic filter. On the chip the composite recovered audio, consisting of carrier component and modulating signal, is passed through a low pass filter amplifier to reduce the carrier component and then is fed to Pin 9 which has an output impedance of ?
The signal still requires further filtering to eliminate the carrier component, deemphasis, volume control, and further amplification before driving a loudspeaker.
The relative level of the composite recovered audio signal at Pin 9 should be considered for proper interaction with an audio post amplifier and a given load element.
The MC is recommended as a low power audio amplifier. The meter output indicates the strength of the IF level and the output current is proportional to the logarithm of the IF input signal amplitude.
A maximum source current of 60? A is available and can be used to drive a meter and to detect a carrier presence. The output at Pin 13 provides a current source. Thus, a resistor to ground yields a voltage proportional to the input carrier signal level. The value of this resistor is estimated by VCC Vdc — 1. A simple inverting op amp has an output at Pin 11 and the inverting input at Pin The noninverting input is connected to 2. The op amp may be used as a noise triggered squelch or as an active noise filter.
The bandpass filter is designed with external impedance elements to discriminate between frequencies. With an external AM detector, the filtered audio signal is checked for a tone signal or for the presence of noise above the normal audio band. This information is applied to Pin Its low voltage design provides low power drain, excellent sensitivity, and good image rejection in narrowband voice and data link applications.
This part combines a mixer, an IF intermediate frequency limiter with a logarithmic response signal strength indicator, a quadrature detector, an active filter and a squelch trigger circuit. Passing through an external bandpass filter, the IF signal is fed into a limiting amplifier and detection circuit where the audio signal is recovered. A conventional quadrature detector is used.
The absence of an input signal is indicated by the presence of noise above the desired audio frequencies. A squelch switch is used to mute the audio when noise or a tone is present. The input signal level is monitored by a meter drive circuit which detects the amount of IF signal in the limiting amplifier. This oscillator can be run under crystal control. For fundamental mode crystals use crystal characterized parallel resonant for 32 pF load.
For higher frequencies, use 3rd overtone series mode type crystals. The mixer is doubly balanced to reduce spurious radiation. This power gain measurement was made under stable conditions using a 50?
The filter impedance closely matches the 1. Since the input impedance at Pin 16 is strongly influenced by a 3. The Smith Chart plot in Figure 17 shows the measured mixer input impedance versus input frequency with the mixer input matched to a 50? In order to assure stable operation under matched conditions, it is necessary to provide a shunt resistor to ground. Figures 11, 12 and 13 show the input networks used to derive the mixer input impedance data.
Following the mixer, a ceramic bandpass filter is recommended for IF filtering i. In this case the meter output can be used directly to trigger the squelch switch when the RF input at the input frequency falls below the desired level.
The level at which this occurs is determined by the resistor placed between the meter drive output Pin 13 and ground Pin An external positive bias to Pin 12 sets up the squelch trigger circuit such that the audio mute Pin 14 is open or connected to ground.
If Pin 12 is pulled down to 0. There is about 57 mV of hyteresis at Pin 12 to prevent jitter. Audio muting is accomplished by connecting Pin 14 to the appropriate point in the audio path between Pin 9 and an audio amplifier. The voltage at Pin 14 should not be lower than —0.
Figure Typical Application for MC at H L2 R11 D1 C1 0. H L2 R13 D1 C1 0. H Coilcraft —07J08 R14 51 k C1 0. H R13 1. Motorola makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does Motorola assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation consequential or incidental damages.
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MC3371 Motorola, MC3371 Datasheet