Building IF amplifiers

Most of the gain and selectivity of a superheterodyne radio receiver are in the intermediate frequency (IF) amplifier. The IF amplifier is, therefore, a high-gain, narrow -bandwidth amplifier. Typically, IF power gams run in the 60- to 120-dB range, depending on the receiver design. It usually has far narrower bandwidth than the RF amplifier For example, 2,8 KHz for an SSB receiver and 500 Hz for a CW receiver. The purpose of the IF amplifier is to provide gain and selectivity to the receiver,...

Cyq

7-11 (A) Untuned (broadband) coupling transformer and (B) winding the transformer on a toroid. Take special note of those two transformers. These transformers are known generally as wideband transmission-line transformers and can be wound on either toroid or binocular ferrite or powdered iron cores. For the project at hand, because of the low frequencies involved, 1 selected a type BN-43-202 binocular core. The type-43 material used in this core is a good selection for the frequency range...

A hypothetical radio receiver

Figure 9-1 shows the block dis gram of a simple communications receiver. We will use this hypothetical receiver as the basic generic framework for evaluating receiver performance. The design in Fig. 9-1 is called a superheterodyne receiver at d is representative of a large class of radio receivers it covers the vast majority of receivers on the market. Other designs, such as the tuned radio frequency (TRF) and direct-conversion receivers (DCR), are simply not in widespread commercial use today....

Receiver improvement strategies

There are several strategies that can improve the performance of a receiver. Some of them are available for after-market use with existing receivers and others are only practical when designing a new receiver. One method for preventing dynamic effects is to reduce the signal level applied to the input of the receiver at all frequencies. A front-end attenuator will help here. Indeed, many modern receivers have a switchable attenuator built in to the front-end circuitry. This attenuator will...

B

2-24 (A) Parallel-resonant LC circuit (B) and Z vs frequency response. Vnftnm- tj't'i entrant in t Hj'Ui ikn' V'. ruiis 45 Choosing component values for LC-resonant tank circuits In some cases, one . f the two basic ty e of resonant., tank cirruil (either series< r parallel) is clearly preferred over tin1 other. hu in other eases oil her rot lit I ho used if il is used correo ly. Por example, in a trap (.i.e., a circuit that pre ems a particular frequency from passing) a parallel-res* nam...

Lowpass highpass bandpass and notch

FUters are frequency-selective circuits that pass some frequencies and reject others. Fillers are available in several different flavors low-pass, high-pass, bandpass, and notch. All of these filters are classified according to the frequencies that they pass (or reject). The breakpoint between the accept band and the reject band is usually taken to be the frequency at which the passband response falls off -3 dB. The four different types are characterized below. Low-pass filters pass all...

Drift problems

The other frequency changing problem is old-fashioned drift. Unfortunately, most electronic components exhibit some temperature sensitivity. This sensitivity is usually measured in terms of a temperature coefficient, which specifies a certain shift of value in pans per million (ppm) per degree Celsius of temperature shift. The temperature coefficient (TV) can be either positive or negative. A positive temperature coefficient (FT,-) indicates the value increase with increases in temperature. A...

Microwave ovens

Most American homes are equipped with microwave ovens. These devices use a magnetron tube to produce several hundred watts of microwave power on a frequency of approximately 2450 MHz. The high voltage applied to the maggie is typically pulsating dc i.e., it is rectified ac, but not rippie-filtered (as are true dc power supplies)). This pulsating dc causes Tiash in radio receivers. Although better-quality microwave ovens are equipped with EM filters, many are not. However, most manufacturers or...

Units of measure

Input signal levels, when specified as a voltage, are typically stated in either microvolts (pnV) or nanovolts (nV) the volt is simply too large a unit for practical use on radio receivers. Signal input voltage (or sometimes power level) is often used as part of the sensitivity specification or as a test condition for measuring certain other performance parameters. TVvo forms of signal voltage that are used for input voltage specification source voltage (Vemf) and potential difference ( d), as...

The pulse source

Almost any source of square waves in the vicinity of 1 MHz can be used for ihe pulse generator. If you have one of those function generators thai oui pul pulses h> 1 MHz or more, then use it. Be careful, however, il the output impedance is 600 l (as some are). For those a you might want to fashion a GOO- to 50-fl transformer or a simple resistor pad. Alternatively, you can build your own pulse sourre. Many different forms ofTTL oscillators can be used as a pulse source, Figure 24-2A showK the...

Varactor applications

Varactors are electronically variable capacitors. In other words, they exhibit a variable capacitance that is a function of a reverse bias potential. This phenomenon leads to several common applications in wl ch capacitance is a consideration. Figure 3-14 shows a typical varactor-tuned LC tank circuit. The link-coupled inductor (I2) is used to input RF to the tank when the circuit is used for RF amplifiers (etc.), The principal LC tank circuit consists of the main inductor (Li) and a...

Inductor circuit symbols

Figure 2-6 shows various circuit symbols used in schematic diagrams to represent inductors. Figures 2-6A and 2-6B represent alternate, but equivalent, forms of lhe same thing i.e., a fixed value, air-core inductor (coil in the vernacular). The other forms of inductor symbol shown in Fig. 2-6 are based on Fig, 2-6A but are just as valid if the open-loop form of Fig- 2-6B is used instead. The form shown in Fig, 2-6C is a tapped fixed-value air-core inductor. By providing a tap on the coil,...

PIN diodes and their uses

Most modem radio transceivers (i.e., frafisnutter rect'iuer) use relayless switching to go back and forth between the receive and transmit states. In many cases, this switching is done with PIN diodes. Similarly, IF filters or front-end bandpass fillers are selected with a front-panel switch that handles only direct current- How Again, PIN diodes. These interesting little components allow us to do switching at RF, IF, and audio frequencies without routing the signals themselves all over the...

Frequency shift problems

Resonant circuits in modern electronic equipment might be LC-tuned by a combination of inductance and capacitance or tun d by & piezoelectric resonator element (crystal). In either event, the cause of a sudden unwanted shift of operating frequency is usually some form of mechanical srauma somewhere in rhe circuit. In other words, some component is either broken or has an intermittent connection. Figure 25-1 shows a partial circuit of an oscillator. The resonance t f this c-irtmi is...

Considerations for good DCR designs

It probably does not surprise many readers that there are some principles of good design that result In superior DCR performance. Some of these principles were discussed by Campbell10 and others.11 Even relatively simple DCR designs, including those based on the Signetics NE-602 integrated circuit double-balanced modulator12 and the I> opular LM-386 audio amplifier, have proven to be very sensitive and free of hum and jnicrophonics, even though that combination is not without critics....

Radio receivers theory and projects

One of the things that fascinated people about radio from its very earliest days is that signals arrive seemingly by magic through the air from long distances, t was very quickly discovered that radio signals are electromagnetic waves exactly like light and infrared, except for frequency and wavelength. Radiowaves have a much lower frequency than light therefore, the wavelengths are much longer. The wavelengths of radio signals range from around 25,000 m at the low-VLF raivge down to...

R1

Where V is Vj and R is Rt or is V- and R is R depe tiding on which voltage drop Is being measured. We can use the voltage divider concept to find either inductance or capacitance by replacing R with the unknown reactance, Consider first the inductive case. In Fig. 16-2B resistor has been replaced by an inductor (LThe resistor Ri is the inductor series resistance. If we measure the voltage drop across (i.e., in Fig. 16-2B) then we can calculate the inductance from As can be noted in Eq. (16-5)...

Installing coaxial connectors

One of the mysteries faced by newcomers to the radio hobbies is the small matter of installing coaxial connectors. These connectors are used to electrically and mechanically fasten the coaxial cable transmission tine from the antenna to the receiver There are two basic forms of coaxial connector, both of which are shown in Fig. 1 -13 (along with an alligator clip and a banana-tip plug for size comparison)- The larger connector is the PL-259 UHF coimector, which is probably the most-common form...

Signal generator for the AM and shortwave bands

The same general type of circuit can be used for the AM band (530 to 1610 kHz) or for the shortwave bands (1610 kHz to 30 MHz). The version shown in Fig- 10-7 uses a standard transformer that has a 217-(mH inductance in the primary winding, Tliis particular example uses a Toko coil from Digi-Key (Part No. TK-I903) in conjunction with a 365-pF broadcast variable capacitor to cover the AM broadcast band. For other frequencies or if F and L are known but C is unknown or if F and C are known but L...

Bandwidth of RFIF transformers

Figure 2-31A shows a parallel-resouam RF IF transformer and Fig- shows the usual construciion in which the two coils and arc wound at distance d apart on a common cylindrical form. The bandwidth of the KF'IF transformer is the difference between the frequencies where the signal voltage across the otil put winding falls off 6 dB from the value at the resonara frequency (F(i), us shown in Fig. 2-31C- If F arid F> are 6-dB (also called the 3-< iB jiohit when signal power is measured instead of...

Basic theory of operation

The DCR is similar to the superheterodyne in underlying concept The receiver radio frequency (RF) signal is translated in frequency by nonlinear mixing with a local oscillator (LO) signal (heterodyning). Figure 6-J shows the basic block diagram for the front end of both types of receiver. The mixer is a nonlinear element that combines the two signals, Frf andFbo. The output of the mixer contains a number of different frequencies that obey the relationship Frp is the frequency of the received...

MOO iH foe lowband VHF

7-Z JFET active preselector circuit. source bias is supplied by the voltage drop across resistor R*2, and the drain load is supplied by a series combination of a resistor and a radio frequency choke (RFCl), The RFC should be 1000 p,H (1 rnH) at the AM broadcast band and HF (shortwave), and 100 jlH in the low-VHF region (> 30 MHz). At VLF frequencies (below the AM broadcast band), use 2,5 mH for RFCl and increase all 0.01-jlF capacitor values to 0J All capacitors are either disk ceramic or one...

AM envelope detectors

An amplitude modulation (AM) signal consists of a slow audio signal which revolves around an average radio frequency (RF) carrier signal. It is essentially a multiplication or mixing process in which the RF carrier and AF signals are both output, along with the (RF AF) and (RF + AF) signals. Because of the selectivity of the transmitter circuits, only the RF carrier and the sum and difference signals appear in the output. The AF signal is suppressed. The sum signal (RF 4- AF) is known as the...

Special variable capacitors

In the preceding sections, the standard forms of variable capacitor were covered. These capacitors are largely used for tuning radio receivers, oscillators, signal generators, and other variable-frequency LC oscillators. This section covers some special forms of variable capacitor The split-stator capacitor Is one in which two variable capacitors are mounted on the same shaft. The split-stator capacitor normally uses a pair of identical capacitors, each the same value, turned by the same shaft....

Circuit Board

15-13 Computer connector fitted viith ferrite beads. The principal offender with respect to noise from computer systems is the monitor, This is because of two factors. First, the deflection circuits tend to operate in frequency ranges (under 40 kHz) that are below many other systems and they have lots of harmonics- Second, those deflection circuits tend to be high-power. The answer to the probiem is to place shielding around the circuits and a common mode choke in the signal line. EMI...

Common mode and differential currents

Noise currents can flow in two modes differential and common mode. These are defined as follows. 15-i Simple L-section filters (A) internal capacitor input type and (B) external inductor input type. 15'7 Several situation* and the filters to implement tliem. 15'7 Several situation* and the filters to implement tliem.

Discriminator circuits

One of the classic FM discriminator circuits is shown in Fig. 27-21. This circuit uses a special transformer that has two secondary windings. One secondary winding is turied slightly above the IF frequency while the other is tuned the same amount below the IF frequency. The two frequencies are spaced slightly more than the expected transmitter swing. Their outputs are combined in a differentia pair of diodes (Py and The outputs of the diodes are connected to load resistors R and Normally, when...

The Smith chart in lossy circuits

Thus far, you have dealt with situations in which loss is either zero (i.e., ideal transmission tines) or so small as to be negligible. In situations where there is appreciable loss in the circuit or line, however, you see a slightly modified situation. The VSWR circle, in that case, is actually a spiral, rather than a circle- Figure 26-10 shows a typical slttiation, Assume that the transmission line is 0.60A long and is connected to a normalized load impedance of Z 1.2 + j 1.2. An MT UBTKt UM...

Prafll

4-7 (A) Flat mounting (B) on-end mounting (C) secured mounting (use nylon machine screws) (D) mounting high-power or high-voltage toroidal inductors or transformer s (E) suspending toroid inductors on a dowel (F) mounting method for a 'single-turn primary transformer in RF watt-meters or VSWR meters. are passed through holes in the board to solder pads underneath. The method of Fig, 4 7B places the toroid at right angles to the board, but it still uses the leads soldered to copper pads on the...

HFVHF buffer amplifier

A buffer amplifier is used to isolate the output of the oscillator from the load, or circuits that follow. Variations in the load of an oscillator can pull the frequency in* correctly so the buffer is used to prevent that problem. Figure 10-5 shows the circuit for a buffer amplifier that can be used in the low-frequency (LF)f high-frequency (HF), and the lower end of the VHF ranges- The amplifier device w the buffer amplifier is a 40673 dual-gate MOSFET transistor (or NTE-222, which is a...

JFET preselector circuits

Figure 7-2 shows the most basic form of JFET preselector. This circuit will work into the low-VHF region. This circuit is in the common source configuration, so the input signal is applied to the gate and the output signal is taken from the drain. The Figure 7-2 shows the most basic form of JFET preselector. This circuit will work into the low-VHF region. This circuit is in the common source configuration, so the input signal is applied to the gate and the output signal is taken from the drain....

Phaseshifted hybrids

The hybrids discussed thus far split the power half to each adjacent port but the signals at those ports are in-phase with each other. That is, there is a 0 phase shift over the paths from the input to the two output ports. There are, however, two forms of phase-shifted hybrids. The form shown in Fig. 12-6A is a 0-l80 hybrid. The sig- 11-5 Combining two antennas in T R switch, nal ovet the path from port 1 to port 2 is not phase-shifted (0 ) while that between pott 1 and port 3 is phase-shifted...

Cl000 Lowlii fain

A type 7809 three-terminal voltage regulator JC will provide 9-Vdc regulated output from a + 12-V (or higher) dc power supply. The use of a voltage-regulated power supply, as described, will also help one problem with this design. The tuning is a function of applied voltage, so it will necessarily change when the battery voltage drops. The receiver in Figs, 5-27 and 5-28 is a superheterodyne model, meaning that it converts the input RF frequency to a lower intermediate...

D

5-26 IF amplifier project (A) completed project (B) input end (C) output end (D) input amplifier stage and (E) output amplifier circuit. when the ATTN is high (i.e., 2.4 V < V < 5.2 V ), then K is energized and inserts the -20-dB attenuator in the path. The IF amplifier of Figs. 5-25 and 5-26 provides about 80 dB of gain at 455 kHz.

Actual circuit details

The actual RF circuit is shown in Fig. 7-12 it is derived from a similar circuit found in Doug DeMaw's excellent book WIFB's QRP Notebook (ARRL, 225 Main Street, Newington, CT 061U). The active amplifier devices are JFETs that are intended for service from dc to VHF. The device selected can be the ever-popular MPF-102 or its replacement equivalent from the SK, ECG, or NTE lines of devices. Also useful is the 2N4416 device. The particular device that I used was the NTE-45I JFET transistor. This...

Tuned radio frequency TRF receivers

The TRF receiver (Fig. 13-3) uses a cascade chain of tuned RF amplifiers 04 Ai, andji3) to amplify the radio signal. The TRF was the first really sensitive design in the early 1920s and was eclipsed by the superhet in popular commercial receivers, But in the VLF range, the TRF is stilt popular especially among homebrewers. A problem with the TRF receiver is the possibility of unwanted oscillations, wliich are common in tuned triode devices, such as MPN bipolar transistors. Peter Taylor's column...

Ab

1*8 SMelded RF construction (A) dosed box showing dc connections made via coaxial capacitors (B) box opened RF construction (e.g., layout, grounding, and shielding) and found that by following the rules, one can be as successful building RF stuff as at lower frequencies. One problem that has always been something of a hassle, however, is the shielding that is required. You could leam layout and grounding, but shielding usually required a better box than 1 had. Most of the low-cost aluminum...

Dynamic range

Reciprocal Mixing

The dynamic range of a radio receiver in the range from the minimum discernible signal to the maximum allowable signal (measured in decibels, dB). Although this simplistic definition is conceptually easy to understand, in the concrete its a ttJe more complex. SeveraJ definitions of dynamic range are used (Dyer, 1993). One definition of dynamic range is that it is the input signal difference between the sensitivity figure (e.g., 0.5 puV for 10 dB S + N N) and the level that drives the receiver...

Winding your own coils

Inductors and capacitors are the principal components used in RF toning circuits. The resonant frequency of a tank circuit is the frequency to which the inductor-capacitor combination is tuned and is found from or, if either the inductance L or capacitance C is known or preselected then the other can be found by solving Eq. 4-1 for the unknown, or In all three equations, L is in henrys, C is in farads, and F is in hertz dont forget to convert values to microhenry's and picofarads after...

Tuning circuit problems

The principal problem to solve in designing and building VLF receivers is the tuning circuits. The capacitance and inductance values tend to be rather large. If you want to use a standard broadcast variable capacitor, which is typically 10 to 365 pF in capacitance value, then a 20- to 30-kHz receiver needs an inductor in the 88-mH range. The calculated value of capacitance needed to resonate 88 mH at 20 to 30 kHz is 720 pF. The reason why a smaller variable capacitance is used is that the...

Directconversion radio receivers

The direct conversion, or synchrodyne, receiver was invented in the late 1920s, but only with the advent of modern semiconductor technology has it come into its own as a real possibility for good-performance receivers. Although most designs are intended for novices, and lack certain features of high-grade superheterodyne receivers, the modem direct-conversion receiver DCR is capable of very decent performance, A case can be made for the assertion that the modern DOR is capable of performing as...

Balanced demodulators

Envelope Detector Full Bridge

Figure 27-9 shows two examples of balanced or full-wave demodulator circuits. These circuits work generally letter than the hall-wave version shown earlier. Figure 27-9A shows the circuit for a conventional full-wave circuit. It depends on two diodes and a center-tapped transformer 7 . It works like the power-supply circuit of the same type. The center tap on the transformer establishes the zero point, or common, so the polarities of the voltages at the ends of the secondary of T are equal but...

Tuned radiofrequency TRF receivers

Trf Receiver Circuit Design

The tuned radio frequency TRF radio uses one or more radio frequency RF amplifiers to boost the weak signal received from the antenna. The simplest form of TRF radio Fig. 5-8 consists of a single RF amplifier stage, with frequency selection LC tank circuits at the input and output. The signal at the antenna input of the RF amplifier is very weak, but because of the amplification of the tube in the amplifier, it is boosted to a stronger level at the output. The RF amplifier is followed by a...

Radially scaled parameters

There are six scales laid out on five lines CD through G in Fig. 26-40 and in expanded form in Fig. 26-5 at the bottom of the Smith chart. These scales are called the radially seated parameters and they arc both very import ant and often overlooked. With these scales, you can determine such factors as VSWR both as a ratio and in decibels , return loss in decibels, voltage or current reflection coefficient, and the power reflection coefficient. The reflection coefficient D is defined as the...

Detector and audio circuits

Once the IF amplifier builds the signal up to a point where it can be successfully demodulated with good volume, you will want a detector circuit to recover the modulating audio. The simplest AM detector is the envelope detector shown in Fig. 5-22. The envelope detector is a single-diode rectifier at the output of the last IF transformer. The diode should be a germanium type, such as 1N34, IN60, 1N270, ECG-109, or NTE-109 devices. A volume-control potentiometer serves as the load for the diode,...

Vqa

23-11 Notch filters wave traps A1 parallel resonant in series with the signal path and B aeries resonant in parallel with the signal path. The resonant frequency is found from. In the practical sense, this equation is not too terribly useful because the better approach is to select a trial value for oil her inductance or capacitance depending on which is more convenient and thor calculate the required value for the other component. These equations are The parallel- and series-resonani circuits...

Stub matching systems

A properly designed matching system will provide a conjugate match to a complex impedance. Some sort of matching syst em or network is needed any time the load impedance Zi. is not equal to the characteristic impedance J 0 of the transmission line. In a transmission-line system, if is possible to use a shorted stub connected in parallel with the line, at a critical distance back from the mismatched load, to affect a match. The stub is merely a section of transmission line that is shorted at the...

Bq 5o

The split capacitor network shown in Fig. 19-4 is used to transform a source impedance that is less than the load impedance. In addition to matching antennas, t his circuit is also used for interstate impedance matching inside communications equipment. The equations for design are One version of the transmatch is shown in Fig, 19-5. This circuit is basically a combination of the split-capacitor network and an output tuning capacitor C3 . For the HF bands, the capacitors are on the order of 150...

Straightline capacitance vs straightline frequency capacitors

Straight Line Frequency Capacitor

The variable capacitor shown in Fig. 3-5 has the rotor shaft in the geometric center of the rotor plate half-circle. The capacitance of this type of variable capacitor varies directly with the rotor shaft angle. As a result, this type of capacitor is called a straight-line capacitance model. Unfortunately, as you will see in a later section, the frequency of a tuned circuit based on inductors and capacitors is not a linear straight line function of capacitance. If a straight line capacitance...

Enhancing AM band reception

Shortwave Pass Filter

Figure 23-9 shows a bandpass filter for the AM broadcast band. This type of filter can be used between the antenna and anteiina input of an AM broadcast band receiver in order to reduce any out-of-band signals that might interfere with reception or reduce the performance of the receiver. This filter consists of a 2000-kHz low-pass filter cascaded with a SCO-kHa high-pass filter. Figure 23-9 shows a bandpass filter for the AM broadcast band. This type of filter can be used between the antenna...

IF amplifier circuits

Amplifier Circuit

The IF amplifier provides most of the gain in a superhet receiver, and it also supplies the narrowest bandwidth in the signal chain. Thus, the IF amplifier is chiefly responsible for both the sensitivity and selectivity nf the radio receiver. In fancy radio receivers, the IF amplifier can be quite complex, as witnessed by the designs used in modern shortwave and ham radio receivers in the kilobuck range. This one is a con siderably simpler design, but is nonetheless effective. For those who...

Audio circuits

The audio chain in the direct-conversion receiver tends to be very high gain in order to compensate for the low output levels usually found on the mixer circuits. The principal job of the audio amplifier is to increase the signal level by an amount that will create comfortable listening level while also tailoring the bandpass characteristics of the overall receiver to limit noise and other artifacts. Although any num ber of discrete and integrated circuit IC circuits are suitable, most...

Direct conversion

Figure 5-24 shows the NE-602 chip used as a direct-conversion receiver. In this type of circuit, the local oscillator LO operates on the same frequency as the received RF signal. As a result, when the two are zero beat., the difference IF frequency is the audio modulating the incoming carrier. In CW reception, the LO is tuned to a frequency a few hundred hertz from the incoming RF. In that case, the difference frequency will be a beat note that is interpreted as a CW signal. Figure 5-24 shows...

Using the doublebalanced mixer DBM

Dbm Mixer Circuit

In radio-frequency electronics, a mixer is a nonlinear circuit or device that permits frequency conversion by the process of heterodyning. Mixers are used in the front end of the most common form of radio, the superheterodyne regardless of wave band , in certain electronic Instruments and in certain measurement schemes receiver dynamic range, oscillator phase noise, etc, . The block diagram for a basic mixer system is shown in Pig. i this diagram is generic in form, but it also represents the...

Wilkinson Combiner

Wilkinson Divider 100mhz

Combining MMIC amplifiers in parallel Figures 22-35 through 22-37 show several MJC applications involving parallel combinations of MIC devices. Perhaps the simplest of these is the configuration f gt f Fig. 22-35. Although each input must have its own de-blocking capacitor to protect the MSG devices internal bias network, the outputs of two or mure MICs might be connected in parallel and share a common power-supply connection and output coupling capacitor. Several advantages are realized with...

A

Vlf Trf Receiver Schematic

13-4 A Block diagram of the VLF SID hunter's receiver and B schematic diagram of circuit. TRF design used 88-mH telephone toroid inductors. The TRF circuit Fig. 3-5 used the 88-mH inductor paralleled by a 365-pF variable capacitor and isolated it for dc by a pair of 100-pF capacitors C and Cs in F g, 13-5 . A problem with the simple circuit of Fig. 13-5 is that it is not easy to adjust the tuning range i.e., the receiver cannot be aligned . A variant on the theme, shown in Fig- 13-6, adds a...

Superheterodyne receivers

Double Balanced Mixer And Oscillator

The superheterodyne radio receiver Fig. 10 was invented in the early 1920s, but only a very few sources could supply them because of patent restrictions. Later, however, patents were pooled as the radio industry grew and eventually the patents expired. Hie superheterodyne design was so superior that within a decade it took over all but a very few radios and is still today the basic design of all AM and FM radio receivers. The block diagram to a superheterodyne receiver is shown in Fig. 5-10....

Ferrite and powderediron rods

Build Ferrite Rod Antenna For Vlf

FetTite rods Fig. 4-12A are used in the low-frequency medium wave, AM broadcast band, and LF VLF receivers to form loopstick antennas. These antennas are often used in radio-direction finders because they possess a 'Tigure-8 reception pattern that counterposes two deep nulls with a pair of main lobes. Another application of ferrite rods is to make balun transformers Fig. 4-12B or filament transformers in vacuum-tube high-power RF amplifiers. Ferrite rod inductors are also used in any...

Variable capacitors in RF circuits

Cylinder Parallel Plate Capacitor

Like all capacitors, variable capacitors are made by placing two wets of meial plates parallel to each other Fig. 3-1 A separated by a diele lt I l ie lt 1 air, mica, ceramic. or a vacuum The difference between variable and fixed capacitors is hat, in variable capacitors, the plates are construcied in such a way Thai the capacitance can be changed. There are two principal ways to vary ihe capacitance either the spacing between the plates is varied or the cross-sectional area of the plaies that...

Inductance of a single straight wire

Although it is commonly assumed that inductors are coils, and therefore consist of at least one, usually more, turns of wire around a cylindrical form, it is also tru lt gt rhai single, straight piece of wire possesses inductance. This inductance of a wire in which the length is at least 1000 times Us diameter lt i ts given by the following 0.005086 y - 0.76 2-4 The inductance values of representative small wires is very small in absolute numbers but at higher frequencies becomes a very...

Converters

A subclass of superheterodyne receivers is the converter technique Fig. 13-2 , in which the VLF band is frequency translated to the high-frequency HF bands. The typical converter circuit is rather simple. An input filter either bandpass or 13-1 Block diagram of a superheterodyne receiver. 13-1 Block diagram of a superheterodyne receiver. t uned to a specific frequency feeds an optional RF amplifier and then a mixer A fixed-frequency crystal oscillator mixes with the RF signal to produce an...

Smith chart components

Impedance Admittance Coordinates

The modern Smith chart is shown in Fig. 26-1 and consists of a series of overlapping orthogonal circles i.e., circles that intersect each other at right angles . This chapter will dissect the Smith chart so that the origin and use of these circles is apparent. The set of orthogonal circles makes up the basic structure of the Smith chart. A baseline is highlighted in rig. 26-2 and it bisects the Smith chart miter circle. This line is called the pure resistance fine, and it forms the reference...

RF directional couplers

Build Directional Coupler

Directional coy piers are devices that will pass signal across one path while passijig a much smaller signal along another path. One of the most common uses of the directional coupler is to sample a RF power signal either for controlling transmitter output power level or for measurement. An example of the latter use is to connect a digital frequency counter to the low-level port and the transmitter and antenna to the straight-through high-power ports. The circuit symbol for a directional...

PIN diode applications

PIN diodes t an be used as either a variable resistor or as an elect ronic switch for RP signals. In the latter case, the diode is basitally a two-valued resistor wilh one value being very high and the other being my low. These characteristics open several possible applications. When used as a switch, PIN diodes can be used to switch devices, such as attenuators, filters, and amplifiers in and out of the circuit. It has become standard prac tice in modern radio equipment to switch dc voltages...

Introduction to negative resistance 1 devices

Gunn Diode Bias Circuit

Onant oscillator circuits use no tuning. They depend on the device dimensions and the average charge carrier velocity through the bulk material to determine operating frequency. Some NDR devices, such as the Gunn diode later in this chapter , will operate in either resonant or unresonant oscillatory modes. Transferred electron devices Gunn diodes Gunn diodes are named after John B. Gunn of IBM, who, in 1963, discovered a phenomenon since then called the Gunn Effect Experimenting with compound...

Broadband RF amplifier 500 input and output

Amplifier Circuit

This project is a highly useful RF amplifier that can be used in a variety of ways. It can be used as a preamplifier for receivers operating in the 3- to 30-MHz shortwave band. It can also be used as a postamplifier following filters, mixers, and other devices that have an attenuation factor. It is common, for example, to find that, mixers and crystal filters have a signal loss of 5 to 8 dB this is called insertion loss . An amplifier following these devices will overcome that loss. The...

Foster Seeley discriminator circuits

Foster Seeley Discriminator

The Foster-Seeley discriminator circuit is shown in Fig. 27-22, while the waveforms are shown in Fig, 27-23. This circuit requires only two tuned circuits rather than the three required by the previous circuit. The output voltage is the algebraic sum of the voltages developed across the R, and R load resistances. Figure 27-23A shows the relationship of the output voltage and the frequency. The primary tuned circuit is in series with both halves of the secondary winding. When the signal is...

Building and using the RF noise bridge

This chapter explores a device that has applications in general RF electronics as well as in antenna work the RF noise bridge. It is one of the most useful, low-cost, and over-looked test instruments in the servicer's armamentarium. Several companies have produced low cost noise bridges Omega-T, PaJoxnar En gineers, and the now out-of-the-kit-business Heath Company. The Omega-T device Fig, 17-1 A is a small cube with minimal dials and a pair of BNC coax connectors marked antenna and receii gt...

RF amplifier and preselector circuits

Mosfet 40673

Low-priced shortwave receivers often suffer from performance problems that are a direct result of the trade-offs that the manufacturers make to produce a low-cost model. In addition, older receivers often suffer the same problems, as do many homebrew radio receiver designs. Chief problems are sensitivity, selectivity, and image response. Sensitivity is a measure of the receiver's abibty to pick-up weak signals. Part of the cause of poor sensitivity is low-gain in the front end of the radio...

Doublesideband DSBSC and singlesideband SSBSC suppressed carrier demodulators

Modulator Ssbsc

Gent content of the speech waveform is fully ecu lamed wilhin one side hand, so the other sideband and can ier are superfluous Figure 27-10 shows a single-sidehand suppressed carrier SSBSC, usually shortened to SSB transmit lt t. The heart of the circuit is a Ut la n eed mod da tor circuit . This circuit is balanced to produce an RF output from the crystal oscillator only when the audio frequency AF signal is present, As a result, the carrier is suppressed in the double-sideband out pur. 27-10...

IF processing ICs

There are several forms of IC used for IF processing. The CA3189E Fig. 8-11 is one of several that are used in broadcast and communications receivers. The input circuitry consists of a fdter, although LC-tuned circuits could be used as well. In this version, the filter circuit is coupled via a pair of capacitors C and CV to the CA3189E. The input impedance is set by resistor Rt and should reflect the needs of the filter rather than the IC filters don't produce the same response when mismatched...

VLF preamplifier

Vlf Preamplifier

The VLF bands run from amp or 10 to 500 kHz or just about everything below the AM broadcast band. The frequencies above about 300 kHz can be accommodated by circuitiy not unlike 455-kHz IF amplifiers. But as frequency decreases, it becomes more of a problem to build a good preamplifier This project is a preamplifier designed for use from 5 to 100 kHz. This band contains a Jot of Navy communications, as well as the most accurate time and frequency station, operated by the National Institute of...

Circuit symbols for capacitors

The circu symbols used to des nale fixed-value capacitors are shown m Fig. 2-13A. Both types of symbols are common. In certain ivpes of capacitors, the curved plateshown on the left in Fig. 2 I' A is usually the outer plate i.e., the one closest to the outside package of the capacitor . This eiui of the capacitor is often indicated by a colored band next to the lead attached to that plate. The symbol for the variable oapaeiior is shown in Fig. 1M3R. The symbol for variable capacitor is the...

Making your own toroidcore inductors and RF transformers

240 Inductor

A lot of construction projects intended for electronic hobbyists and amateur radio operators call for inductors or radio-frequency RF transformers wound on toroidal cores, A toroid is a doughnut-shaped object, i.e., a short cylinder often with rounded edges that has a hole in the center see Fig. 4-4 . The toroidal shape is desirable for inductors because it permits a relatively high inductance value with few turns of wire, and, perhaps most important, the geometry of the core makes it...

9

5-19 Another view of the NE-602 integrated circuit. Figure 5-20 shows a simple superheterodyne converter circuit based on the NE-602IC- The input circuit is broadbanded by using an RF transformer built on a toroid powdered-iron form. The turns ratio LjLi is typically 10 1 to 12 1 i.e., there are 10 to 12 turns on L2 for every turn on Lv Experiments and published data show good starting numbers are 20 to 24 turns on L gt t with 2 to 3 turns in Lt for frequencies in the upper shortwave region. As...

Mechanicalfilter IF amplifier

Selectivity is one of the 'holy grails of receiver designers and in many instances is more important than sensitivity or certain other specifications. The selectivity of the receiver is a measure of its ability to reject unwanted signals. The selectivity of a receiver is usually specified as the bandwidth between the points on the bandpass characteristic, where the gain falls ofT -6 dB voltage from the midband response. Also important is the skirt factor, which is a measure of the shape of the...

Building simple VLF radio receivers

The very tow frequencies VLF are located between a few kilo hertz and around 300 kHz, depending on whose definition is used. For purposes of this chapter VLF represents the 5- to 100-kHz region. The reason for this seemingly arbitrary designation is that many ham-band and SWL communications receivers operate down to 100 kHz and only a few operate below that limit. A lot of radio stations are active in the region below 100 kHz, Perhaps the best-known station is WWVB on 00 kHz. This station is...

J

Feedback oscillator circuits A Armstrong, B Colpitts, and C Hartley. 1 - to ' 0-MHz crystui oscillator 245 The resonator of the oscillator could bo either an inductor-capacitor LC tuned circuit, as shown in the examples of Fig. 10 2, or a piezoelectric crystal resonator. The latter are single-channel resonators, but are more stable than LC-tuned circuits, Figure 10-3 shows a simple, nearly universal signal generator that cart accommodate crystal frequencies between 1 and 20 MHz. This oscillator...

MOSFET preselector circuits

Preselector Circuit

7-6 MOSFET active preselector circuit. 7-6 MOSFET active preselector circuit. The inductors are of the same sort as described. It is permissible to put and Ls in close proximity to each other, but these should be separated from L4 in order to prevent unwanted oscillation because of feedback arising from coil coupling. The circuit in Fig. 7-7 is a little different. In addition to using only input tuning which lessens the potential for oscillation , it also uses voltage tuning. The hard-to-find...

Op Amp Vlf Converter Sales

Vlf Sid Receiver

Tuning circuit using one fixed and one variable inductor. 13-7 Mutual reactance coupling Ay capacitance and B inductance. In Fig. 13-7A, a small capacitance 33 to 120 pF is used to couple the two LC resonant circuits Li CiA and L Cib . In Fig. 13-7B, a common inductor Lf is used for the same purpose. Experiments show that a value of 150 to 700 iH is needed for The ARRL Handbook for Radio Amateurs all recent editions provides details on selecting values for the components in these circuits. A...

E

Oscillatore Hartley Ne602

5-17 Local oscillator circuits for the KE-603. If the capacitor values are Incorrect, the oscillator will either fail to run or will operate intermittently. Generally, an increase in the capacitances will suffice to make A problem with the circuit of Fig, 5-17A is that the crystal frequency i not controllable. The actual operating frequency of any crystal depends, in part, on the circuit capacitance seen by the crystal. The calibrated frequency is typically valid when the load capacitance is 20...

How To Make A 4-1 Balun On A Single Core

Impedance Matching Transformer

4-1S Inductive-loop dilution-finding antenna, where A is the length of each side in centimeters cm B is the width of the coil in centimeters cm N is the number of turns in the coil close wound ft and AT are 0.008, 1.4142, 0.37942, and 0.33113 respectively. Whenever conductors are placed side by side, as in the case of the loop-wound coil, there is a capacitance between the conductors even if formed by a single loop of wire, as in a coil . This capacitance can be significant when dealing with...

Filter switching in IF amplifiers

Switching filters is necessary to accommodate different modes of transmission. AM requires 4 or 6 KHz on shortwave and 8 KHz on the AM broadcast band BCB . Single-sideband requires 2,8 KHz, RTTY RATT requires 1,8 KHz, and CW requires either 270 or 500 Hz. Similarly, FM might require 150 KHz for the FM BCB and as lit-t e as 5 KHz on landmobile communications equipment. These various modes of transmission require different filters, and those filters have to be switched in and out of the circuit....

References and notes

The Sky Chorus, Popular Electronics, July, p. 46. Mideke, M. 1992 . Listening to Nature's Radio Science Probe , July, p. 87, Pine, B. High School Support for Space Physics Research. Unpublished paper sent to participants in Project INSPIRE. T amp ylor, P,F and Stokes, A. 1991 . ''Recording Solar Flares Indirectly. Ccmimunica- tions Qttanerly, Summer, p. 29, Taylor, P. 1993 . The Solar Spectrum Update on the VLF Receiver. Communications Quarterly, Spring, p. 51,

Universal IF amplifier

Antenna Inductance

The IF amplifier in Fig. 8-5 is based on the popular MC- 1350P integrated circuit. This chip is easily available through any of the major mail order parts houses and many small ones. It is basically a variation on the LM-1490 and LM-159G type of circuit but is a little easier to apply. If you have difficulty locating MC-1350P devices, the exact same chip is available in the service replacement lines such as ECG and NTE. These parts lines are sold at 8-5 IF amplifier with crystal filter. local...

Shortwave receiver project

This section shows a simple radio n tviver kit that will provide startlingly good performance for a very low cost. It is not the equal of a 1000 conimunications re-ceiver, btit it provides reasonably good performance in the HF shortwave band for only a few dollars. Perhaps most important is the fact that it serves as a good building block to add on, other circuits. Construction projects have long been part of the radio hobby today, it is easier than ever before. A number of companies make small...

Desensitization

Passive Preselector Design

The desensitization problem is a severely reduced receiver sensitivity caused by the presence of a strong local signal. Desensitization can occur across a wide frequency spectrum, not only in the band where the offending signal is located. The strong offending signal jnight not be heard, except when the receiver is tuned to or near its frequency. It the signal is strong enough to drive the RF amplifier of the receiver into non-linearity then it might generate harmonics integer multiples of the...

Amidon Associates coil system

It was once difficult to obtain coil forms to make your own project inductors. Amidon Associates Inc. makes a series of slug-tuned inductor forms that can be used to make any-value coil that you are likely to need. Figure 4-2A shows an Amidon form, and Fig. 4-2B shows an exploded view. Prorata maximum eleciralatk shielding CUP CORE Same material as tuning slug. Provides maximum magnet shietfng Mater l icfectwj foe opcfaitkt twjwency. - BOBBIN Supports winding SIX PIN BASE r 4-2 Shielded...

455kHz AM IFamplifier testandalignment oscillator

455khz Generator

The modern superheterodyne AM radio uses a 455-kHz IF amplifier 262,5 kHz is used on AM car radios . Figure 10-6 shows a simple signal-generator circuit, that can be used to test, troubleshoot, or align the AM IF stage Ln common radios- The active element is a MPF-102 or NTE-312 JFET. As you can see by comparing Fig. 10-6 to Fig, 10-2, this circuit is of the basic Hartley oscillator class because it uses a tapped inductor 7 in the feedback network. The transformer used for this purpose is a...

The basis of TDR

Time-domain reflectometry works on the principle that waves on a nonmatched transmission line reflect. The waveform sern at any given point alnrig Ihe line is the algebraic sum of the forward and reflected waveforms. In TDR measurements, we look at the waveform at the input end of The transmission lino system. Figure 24-1 shows the basic set-up for our impromptu T R. A pulse generator, or other source of 1-MHz square waves, is applied simultaneously to the vertical input of an oscilloscope and...

Broadband RF preamplifier for Vlf Lf and AM BCB

100khz 30mhz Preamp

In many situations, a broadband as opposed to tuned RF amplifier is needed. Typical applications include boosting the output of RF signal generators which tend to be normally quite low level , antenna preamphfication, loop antenna amplifier, and in the front ends of receivers. A number of different, circuits published, including some by me, but one failing that I've noted on most of them is that they often lack response at the low end of the frequency range. Many designs offer 3 dB frequency...

Ratio detector circuits

The ratio detector circuit is shown in Fig. 27-24, This circuit uses a special transformer in which there is a small capacitor between the center tap on the primary winding and the center tap on the secondary winding. Note that the diodes an1 27-24 Waveforms for FM demodulation. connected to aid each other rather than buck each other, as was the ease in the Foster-Seeley discriminator circuit. When the signal is unmodulated, the voltage appearing across R is one-half the AGO automatic gain...

Broadband or tuned RFIF amplifier using the MC1350P

The MC- 1350P is a variant of the MC-1590 device, but unlike the 159 1, it is available in the popular and easy-to-use eight-pin mini-DIP package. It has gain sufficient to make a 30-dB amplifier, although it is a bit finicky and tends to oscillate if the circuit is not built correctly. Layout, in other words, can be a very critical factor because of the gain. If you cannot find the MC-1350P, use the NTE -746 or ECG-746. These devices are MC-1360Ps, but are sold in the service and maintenance...

Some practical design approaches

Double Balanced Antenna

The literature on DCRs has several different popular approaches, anil each has its own place. Some of the simpler designs are based on the combination of a Signetics NE-602 device and a LM-386 IC audio section. Others are based on different 10 Rick Campbell, KK7B, -LHigh Performance Direct-C-onversion Receivers, QST. August i992 up 19-28. 11 ost August 1980, pp. 14-19 PaulG DauJton, K5WMS, The Explorer HF Receiver for 40 and Si Meters. 73 Amateur Radio 7bday, August 1992, pp 30-rt4 John Dillon,...

Introduction to RF electronics

Radio-frequency RF electronics differ from other electronics because the higher frequencies make some circuit operation a little hard to understand. Stray capacitance and stray inductance afflict these circuits. Stray capacitance is the capacitance that exists between conductors of the circuit, between conductors or components and ground, or between components. Stray inductance is the normal inductance of the conductors that connect components, as well as internal component inductances- These...

The electromagnetic spectrum

When an RF electrical signal radiates, it becomes an electromagnetic wave that includes not only radio signals, but also infrared, visible light, ultraviolet light, X rays, gamma rays, and others. Before proceeding with RF electronic circuits, therefore, take a look at the electromagnetic spectrum. The electromagnetic spectrum Fig. 1-1 is broken into bands for the sake of convenience and identification. The spectrum extends from the very lowest ae frequencies and continues well past visible...