Superheterodyne receiver project

superheterodyne receiver project

Some had 1. The 1. While I own a few antique radios, I have nothing in my collection that uses any of these tubes. So, I decided to come up with some project that would put them to good use. My intention was to build a battery powered radio, and to find a way to use the 2 volt filament tubes powered from readily available batteries.

I decided that the simplest approach would be to use tubes with identical filament current ratings and then connect them with the filaments in series. With this in mind, I chose tubes with 60 mA filaments, and limited the design to a three tube circuit. My intention was to use the 1D7 in its standard application to mix the incoming RF signal down to the intermediate frequency of kHz, then use the 1D5 as a regenerative detector, providing both IF gain and selectivity, as well as audio detection.

The 1H4 would then be used as a final audio amplification stage. Receiver designs like this were fairly common many years ago, and gave reasonable performance with relatively few parts. Two such examples are the Philco models 80 and 84 though these were AC powered and therefore included a fourth tube as rectifier. There were others as well. I have redrawn that circuit, and it is shown here:.

It should be pointed out that this circuit was not intended for a battery supply and uses tubes which draw a lot of heater current. But I hoped that it would be adaptable to battery tubes. The circuit is quite simple, and does not require any hard to find coils. Except for the 2.

This circuit has received many good reviews over the years, and as such, seemed to be a good basis for the present project. Filament Wiring. My first concern, was that my chosen tubes were never designed for series filament operation, and there was no guarantee that the filaments would heat evenly.

This is wasteful of battery power, and so I decided to do some measurements with several tubes to see how the filament voltage varied from tube to tube, with the hope that equalizing resistors would not be required. I connected the filaments of three tubes in series to a variable power supply and brought the voltage up slowly until the highest voltage across any filament reached 2. Tube Set 1. Not too promising. So, I swapped out the 1H4 for a different one and then got this result:.

superheterodyne receiver project

Tube Set 2. Nor did I want to resort to a power wasting resistor network. As an alternative, I decided to try a series chain of rectifier diodes.

Using a string of nine 1N diodes, I connected three across each filament. The diode forward voltage being 0. This worked very well. The voltage balance across the filaments improved dramatically, and there was surprisingly little overall increase in current due to the diodes.

Superhet / Superheterodyne Radio Receiver Basics

The results are as follows:.One Tube Direct Conversion Receiver. This project makes interesting use of the unique characteristics of a 6JH8 beam deflection tube. I used this in the Summer Homebrew DX contest and logged stations with it. More info …. One Tube 2xReflexed Superheterodyne Receiver. Based on a 6ME8. Not a multi-section tube, but just a single active device that can drive a speaker on DX.

Two Tube Superheterodyne Receiver. This was my first Superhet project. Screen modulation with carrier control. Uses a 6M11 Compactron 3-section tube. Many of the projects described on these pages operate at voltages which are high enough to injure or kill.

Do not attempt to build or operate any of these projects unless you are properly trained to work with these voltages. Uses a 6CQ8 2-section tube. Mystery Crystal Set. An ever popular design. Other Projects:. FM Crystal Radio. A true frequency discriminator circuit. Two chips and a few passive components. Yes, it really is possible!

No IC's; no transistors; just three tubes. Uses two 6CQ8's and one 6HA5. Tube Audio Amplifier. A low power amplifier to drive desktop speakers. Vintage Style 3-Tube Superheterodyne Receiver. Direct frequency entry to 1 Hz resolution, and a sweep function. Proceed at your own risk! Screen modulation with carrier control Uses a 6CQ8 2-section tube.In superheterodyne radio receivers, the incoming radio signals arc intercepted by the antenna arid converted into the corresponding currents and voltages.

In the receiver, the incoming signal frequency is mixed with a locally generated frequency.

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The output of the mixer consists of the sum and difference of the two frequencies. The mixing of the two frequencies is termed heterodyning. Out of the two resultant components of the mixer, the sum component is rejected and the difference component is selected. The value of the difference frequency component varies with the incoming frequencies, if the frequency of the local oscillator is kept constant. It is possible to keep the frequency of the difference components constant by varying the frequency of the local oscillator according to the incoming signal frequency.

In this case, the process is called Superheterodyne and the receiver is known as a superheterodyne radio receiver. In Figure the receiving antenna intercepts the radio signals and feeds the RF amplifier, The RF amplifier selects the desired signal frequency and amplifies its voltage, The RF' amplifier is a small-signal voltage amplifier that operates in the RF range. This amplifier is tuned to the desired signal frequency by using capacitive tuning.

After suitable amplification of the RF signal it is fed to the mixer. The mixer takes another input from a local oscillator, which generates a frequency according to the frequency of the selected signal so that the difference equals. The mixer consists of a non-linear device, such as a transistor. Due to the non-linearity, the mixer output consists of a number of frequency components.

It provides sum and difference frequency components along with their higher harmonics. A tuned circuit at the output of the mixer selects only the difference component while rejecting all other components.

The difference component is called the intermediate frequency or IF the value of IF frequency is always constant and is equal to KHz. For a constant IF frequency for all incoming signals, the frequency of the local oscillator is adjusted using capacitive tuning. The incoming signal is also selected using capacitive tuning. The two capacitors used to select the incoming signal and the oscillator frequency is ganged together so that the tuning of both the RF amplifier and the local oscillator circuits is done simultaneously.

This arrangement ensures that the local oscillator has the correct frequency to generate constant IF frequencies.

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The mixer stage is also tuned to IF frequency using capacitive tuning. The tuning capacitor is also ganged with the RF amplifier and the local oscillator. Thus all the three stages are tuned at the same time to the required frequency through the ganged Capacitor, which consists of the three tuning capacitors. The IF signal is fed to an IF amplifier with two amplifier stages.The Supersonic Heterodyne receiver, or Superheterodyne receiver uses frequency mixing to convert a received signal to a fixed intermediate frequency IF which can be more conveniently processed than the original carrier frequency.

At the cost of an extra frequency converter stage, the superheterodyne receiver provides superior selectivity and sensitivity compared with simpler designs. Superheterodyne receivers have better performance because the components can be optimized to work a single intermediate frequency, and can take advantage of arithmetic selectivity.

So, the incoming radio signal is mixed with a local oscillator to produce sum and difference frequency components. The lower frequency difference component called the intermediate frequency IFis separated from the other components by fixed tuned amplifier stages set to the intermediate frequency. The tuning of the local oscillator is mechanically ganged to the tuning of the signal circuit or radio frequency RF stages so that the difference intermediate frequency is always the same fixed value.

The superheterodyne design is nearly or may already be depending on when you are reading this years old. Although it has been around a long time, the design is still the most widely used today. New semiconductor technology and high levels of integration have kept the superheterodyne architecture vitalized and in popular use both in the transmit and receive application.

The antenna collects the radio signal. The tuned RF stage with optional RF amplifier provides some initial selectivity and prevent strong out-of-passband signals from saturating the initial amplifier.

superheterodyne receiver project

A local oscillator provides the mixing frequency. The oscillator is typically a variable frequency oscillator which is used to tune the receiver to different stations.

The frequency mixer then changes the incoming radio frequency signal to a higher or lower, fixed, intermediate frequency IF. The IF band-pass filter and amplifier supply most of the gain and the narrowband filtering for the radio. The demodulator extracts the audio or other modulation from the IF radio frequency. Finally, the extracted signal is then amplified by the audio amplifier. Heterodyning is the mixing of two frequencies together so as to produce a beat frequency.

With AM Amplitude Modulation the information signal is mixed with the carrier to produce the side-bands. The side-bands occur at precisely the sum and difference frequencies of the carrier and information. Superheterodyning is creating a beat frequency that is lower than the original signal. The lower side band and the difference between the other of the mixed frequencies is superheterodyning.It is useful to have an understanding of the different signal blocks, their functions, and the overall signal flow, not only for the RF circuit design, but also from an operational viewpoint.

It is possible to get the best performance by understanding its internal RF design and function. There are several different circuit blocks that make up the overall receiver, each one has its own function. Whilst the superheterodyne receiver block diagram below is the most basic format, it serves to illustrate the operation. More complicated receivers with more complicated block diagrams are often seen as these radios are able to offer better performance and more facilities.

There are some key circuit blocks within the RF design of the basic superheterodyne receiver. Although more complicated receivers can be made, the basic RF circuit design is widely used — further blocks can add improved performance or additional functionality and their operation within the whole receiver is normally easy to determine once the basic block diagram is understood.

It also provides some amplification. There are many different approaches used within the RF circuit design for this block dependent its application. The RF circuit design presents some challenges. Low cost broadcast radios may have an amplifying mixer circuit that gives some RF amplification. HF radios may not want too much RF gain because some of the very strong signals received could overload later stages. The RF design may incorporate some amplification as well as RF attenuation to overcome this issue.

Radios for VHF and above will tend to use more gain to have a sufficiently low noise figure to receive the signal. If noise performance for the receiver is important, then this stage will be designed for optimum noise performance. This RF amplifier circuit block will also increase the signal level so that the noise introduced by later stages is at a lower level in comparison to the wanted signal.

Early receivers used free running local oscillators. There was a considerable degree of RF circuit design expertise used with these oscillators in high performance superhet radios to ensure the lowest possible drift.

High Q coils, low drift circuit configurations, heat management because heat causes driftetc. Today most receivers use one or more of a variety of forms frequency synthesizers. The most common approach in the RF circuit design is to use a phase locked loop approach. Single and multi-loop synthesizers are used. Direct digital synthesizers are also being used increasingly.

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Whatever form of synthesizer is used in the RF design, they provide much greater levels of stability and enable frequencies to be programmed digitally in a variety of ways, normally using some form of microcontroller or microprocessor system.

Ensuring that the mixer performance matches that of the rest of the radio is particularly important. Both the local oscillator and incoming signal enter this block within the superheterodyne receiver. The wanted signal is converted to the intermediate frequency.Virtually all broadcast radio receivers, as well as televisions, short wave receivers and commercial radios have used the superheterodyne principle as the basis of their operation. Invented in to overcome the issues of lack of selectivity, superhet designs have been at the centre of radio communications technology for nearly years, and only recently are other topologies taking over.

Despite this the superheterodyne radio is still used in many applications and the RF design techniques used are still applicable in many radio communications applications. The superheterodyne radio receiver, although the RF circuit design is more complicated than some other forms of radio set, offers many advantages in terms of performance, particularly its selectivity.

superheterodyne receiver project

The superhet radio converts signals to a fixed frequency intermediate frequency, and this enables it to remove unwanted signals more effectively than other forms like the TRF Tuned Radio Frequency sets or even regenerative radios that were used particularly in the early days of radio. The superhet radio used to be the undoubted radio receiver technique of choice. It was almost universally used. However, nowadays with software defined radios taking over the superhet is used less widely.

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The superhet was used in every form of radio from domestic broadcast radios to walkie talkies, television sets, through to hi-fi tuners and professional communications radios, satellite base stations and much more. The story of the development and RF circuit design technology of the superheterodyne radio receiver can be traced back to the earliest days of radio.

Reginald Fessenden noticed that signals on adjacent wavelengths created a beat note together. Later in during the First World War the benefits of using radio technology started to be realised and the need to radios that were selective and provided sufficient gain and sensitivity were needed. Several engineers tackled the problem: Lucien Levy in France, Walter Schottky in Germany and finally the man to whom the superheterodyne technique is credited, Edwin Armstrong who built the first working superhet radio.

The superheterodyne radio was invented in an age when radio technology was very basic and radio receiver performance lacked what we would take for granted today. Read more about the fascinating story of the invention of the superheterodyne radio receiver. This enables signals to be translated from one frequency to another.

The input frequency is often referred to as the RF input, whilst the locally generated oscillator signal is referred to as the local oscillator, and the output frequency is called the intermediate frequency as it is between the RF and the audio frequencies.

This enables an incoming frequency to be translated down to a fixed frequency where it can be effectively filtered. Varying the frequency of the local oscillator enables the receiver to be tuned to different frequencies.

It is possible for signals on two different frequencies to enter the intermediate frequency stages. RF tuning removes one and accepts the other. When image signals are present they can cause unwanted interference, masking out wanted signals if both appear at the same place within the intermediate frequency section. Often in low cost radios, harmonics of the local oscillator can track at different frequencies giving rise to varying heterodynes as the receiver is tuned.

Good image rejection is one of the keys to a high performance radio receiver.

AM Superheterodyne receiver

The basic block diagram of the superheterodyne receiver enables the overall operation of the radio to be understood. In more sophisticated radios, there will be additional blocks added to the basic block diagram.

There may be additional blocks for additional demodulators, or there can be additional circuit blocks within the local oscillator, dependent upon the level of details required. In addition to this some superheterodyne radios may have two or more conversions to provide enhanced performance in a variety of respects. As a result of its advantages the superheterodyne receiver has remained as one of the foremost techniques used in radio technology.

Although today, other techniques are coming to the fore increasingly, nevertheless the superhet receiver is still very widely used in view of the benefits it is able to offer. Using fixed frequency filters it is able to provide excellent adjacent channel rejection. By using a fixed frequency intermediate stage, fixed frequency filters can be used.Introduction: Building a receiver such as the 6x2 receiver is a formidable project and should not be entered into lightly.

Building a tube superheterodyne receiver or SSB transmitter is perhaps the most difficult project a builder can ever undertake.

As manufacturers in the s and s quickly found, robust construction is necessary, particularly when it comes to the local oscillator and BFO components.

These components must be mounted very securely to avoid drift and microphonics. Fortunately for us, these requirements are somewhat easier in the 6x2 receiver because, except when receiving WWV, the local oscillator always operates on the same frequency. The number of sensitive components in the local oscillator is much less than the number required in a general coverage or five band receiver, and this makes construction much easier.

For example, there is only one local oscillator coil rather than five or six, and this greatly simplifies construction. Tube gear utilizes components that are larger and heavier than solid state gear, and this means the chassis must be stronger to handle the extra weight.

Heavy components, such as transformers and chokes, must be mounted as close to the sides and other support structures as possible. This minimizes flexing of the chassis, which can lead to frequency instability and microphonics. The main tuning capacitor must be mounted in a very stiff area where any movement is impossible, and the alignment between the vernier dial and the main tuning capacitor must be adjustable so that any biniding can be eliminated.

The movement of the main tuning capacitor and vernier dial must be absolutely smooth if good tuning characteristics are to be achieved. Approximate Dimensions: The main chassis of the 6x2 receiver is a box constructed of aluminum sheet and bar stock. A thick front panel made of aluminum sheet is then securely fastened to the box.

The main chassis dimensions are approximately 12" wide, 9" deep, and 3" high. If you zoom in on this super detailed side view you will get a good idea of how the chassis and front panel are structured. Main Chassis Construction: The main chassis of the 6x2 receiver is a box constructed of aluminum sheet and bar stock.

This is the same construction that I used in my Amplifier and my Wingfoot Amplifier. Rigid construction, so neccessary for stability, is even more important in a receiver than it is in an amplifier. Note that the front panel does not form the front side of the chassis. It also provides strength and support to the front side of the top panelwhich is very important. Do not omit it!

This extra panel is more easily seen in the photo below. If you zoom in on this super detailed rear view you will get a good idea of how the main chassis and front panel are put together. If you carefully look at the back panel at the rear of the photo you will also two see small "L" brackets that are attached to the middle of the back panel. One is behind the white ceramic resistor at the rear of the photo.


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