Ham Radio Exam – Block Diagrams

Placement of Component in an HF Station (B-003-001)

How it works

The above diagram represents a typically setup in a well-designed and equipped amateur radio station. It is not necessary to have all of the components listed above but for the sake of completeness we will discuss all of them.

Two necessary components are a Transceiver and an antenna. In fact, in mobile operations such as using an HT on 2 M that is all the components you would have.

In a station where you want to run multiple frequencies you will typically have more than one antenna. You can choose which antenna to use by using the Antenna Switch.

If you are operating below 14 MHz you will typically want to use an Antenna Tuner because variations in your operating frequency can have big effects on how well your antenna is matched to your Transceiver. This is the case with Most Antennas When Operating below 14 MHz. You can measure the amount of mis-match between your Transceiver and the antenna by using the SWR Bridge.

Most Antennas When Operating above 14 MHz do not require tuning after their initial construction in order to work.

While tuning up the radio it is very bad practice to tune up into an antenna. Your radio signals could be broadcast all around the world and affect other people. Thus while tuning up, you would use a Dummy Load. This behaves like an antenna as far as the radio is concerned but doesn't broadcast around the world. (Note: There will still be some radiation of signal so you should treat the tune-up portion just like you were on the air.)

In some cases a ham operator may decide his radio does not put out a strong enough signal. There are several options available. Probably the best is to look at an improved antenna design that radiates a better signal. Another option is to boost the signals using a Linear Amplifier.

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Before the signal from the radio is sent to that antenna it is passed through a Low-Pass Filter Especially with older tube-type radios the radio signal going to the antenna could contain higher frequency overtones in addition to the intended signal. These overtones could interfere with broadcast T.V. reception. The Low-Pass Filter removes these overtones.

Single Sideband Transmitter (B-003-006)

How it works

This SSB transmitter uses a two stage conversion process to create the final signal. You speak into the Microphone and the output of the microphone is amplified by the Speech Amplifier. The result is feed into a Balanced Modulator along with a radio frequency signal generated by the Radio Frequency Oscillator.

A Balanced Modulator is a special device that takes a voice signal and a carrier, combines them, and passes on only the upper and lower sidebands. Since this radio is a SINGLE Side Band radio one of the side bands must be suppressed. This is done by the Filter.

The remaining sideband is fed into the Mixer along with a radio frequency signal generated by the Variable Frequency Oscillator. The Variable Frequency Oscillator provides a means of tuning the radio to the desired transmission frequency. The output frequency will actually be a combination of the frequencies of the Radio Frequency Oscillator and the Variable Frequency Oscillator. This needs to be taken into account then by the radio's designer(s).

The output signal from the Mixer will still be quite weak so it is fed into the Linear Amplifier. It is very important that the amplifier does not introduce any distortion because the effects would be noticeable at the receiving end. Finally the signal is fed to the Antenna.

Single Sideband and CW Receiver (B-003-005)

How it works

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A Single Sideband and CW receiver works much the same way as an AM receiver works. In fact, some textbooks begin with the AM receiver and then treat the single sideband receiver as a modification. We will not follow this practice but will begin with a discussion of the AM receiver in general and then describe the sideband receiver in detail.

Typically, an AM signal consists of a carrier and two side bands, one on each side of the carrier. It would be sufficient to send only one of the sidebands and still recover the AM signal but traditionally both sidebands were sent.

In contrast, a Single Sideband transmitter only sends ONE sideband. The minimum necessary to decode the signal is one sideband and a carrier. The Single Sideband receiver provides its own carrier in the form of a Beat Frequency Oscillator. Let's look at the stages in detail.

Radio signals enter the Antenna. These signals are amplified by the Radio Frequency Amplifier During these two stages some elimination of undesired signals takes place but not very much.

The resulting signals are combined with the signal from the High Frequency Oscillator in the Mixer and the result is passed through a Filter. The result is the original sideband but at a much lower frequency. This signal is amplified by the Intermediate Frequency Amplifier.

If this were an AM receiver the resulting sideband would also be accompanied by a carrier and this would be sent to a detector to obtain the AM audio signal. But since this is a Single Sideband receiver an appropriate carrier is re-inserted by the Beat Frequency Oscillator and the two signals are combined in the Product Detector. The output is an audio signal. This signal is sent to an Audio Frequency Amplifier and then converted to sound by the Speaker and/or Headphones.

Frequency Modulation Transmitter (B-003-002)

How it works

The signal from the Microphone is amplified by the Speech Amplifier to make them stronger. The result is passed through the Modulator. The modulator controls the Oscillator and varies the frequency based on the signal from the microphone.

The output of the oscillator is passed through the Frequency Multiplier which changes the signal into one at the appropriate frequency for sending. This signal is then amplified in the Power Amplifier and sent to the Antenna.

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Frequency Modulation Receiver (B-003-003)

How it works

The Antenna receives the radio signals and passes them to the Radio Frequency Amplifier to make them stronger. The result is combined in a Mixer with the output of the High Frequency Oscillator. The result is a radio signal of a much lower frequency range. This range is fixed and determined during the design of the radio. This signal is passed through a Filter.

The output of the Filter is then amplified by the Intermediate Frequency Amplifier and sent on to the Limiter.

When the signal leaves the Intermediate Frequency Amplifier it may have a varying amplitude as well as a varying frequency. The job of the Limiter is to remove the A.M. components of the signal.

Now comes the part where we get the information out of the signal. Remember the information is encoded as changes in the frequency of the signal. The Frequency Discriminator takes the variations in frequency and changes them into variations of amplitude. The result is an audio signal.

This audio signal is amplified in the Audio Frequency Amplifier and the result is sent to the Speaker and/or Headphones.

The Digital System (B-003-007)

How it works

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This diagram is somewhat different form the others in that the information flows two ways. The end user gets data from the Computer or inputs data into the computer in the Input/Output stage. This input could be from the keyboard as in PSK31 or Packet Radio and the output is typically to the video monitor. The input/output could be from the internet as in IRLP.

Typically one cannot just plug a computer directly into a transceiver so the data is first passed through a Modem as is the case in Packet Radio. With PSK31 and IRLP the computer's sound card as well as some special circuitry attached typically to the serial port of the computer is used in place of the modem.

The Transceiver either converts the output of the modem into radio waves (while transmitting) or converts the radio waves into a form that the modem can accept (while receiving).

Finally, the Transceiver is connected to an Antenna which propagates/detects radio waves.

The Yagi-Uda Three-Element Directional Antenna (003-009)

Reflector Driven Element Director

How it works

A Yagi-Uda Directional Antenna works something like a spot light. With a spot-light you have a filament which generates the light. Typically there is a lens in front of the light to focus the beam, and a mirror behind the light to reflect light that was originally going backwards.

In the Yagi-Uda antenna, the filament of the bulb is replaced by the Driven Element It is the only element actually attached to the radio. Behind the Driven Element is a parasitic element called the Reflector which acts like the mirror in the spot light. In front of the Driven Element is another parasitic element called the Director. This acts like the lens part of the spot light.

In order to make the whole thing easy to rotate, each of the elements is mounted on a Boom.

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Boom

The Regulated Power Supply (B-003-008)

How it works

A Power Supply is a power transformer. The power supply takes electricity that is in the wrong form and converts it into the right form.

For example, suppose you wanted to run a 12V D.C. radio from the electricity in your house. The Input electricity would be 120 V A.C. The Output that you want is 12 V D.C. So first the input voltage is sent through a Transformer to change it to 12 V A.C. Now the voltage is correct but it is still A.C. and we want D.C. The next step is to send the electricity through a Rectifier to change from A.C. to D.C.

We are almost done but there are still a few problems. The electricity we have at this stage is 12 V D.C. but there will be ripples. If you were to plug your radio into this supply you would typically hear a "hum". This hum is caused by the electricity not being at a constant voltage but having ripples. These ripples are removed by means of a Filter.

Also, one of the real world problems (as opposed to this theoretical discussion) is that the voltage may not always be 12 V. Typically if the power supply is under low load (like before you turn the radio on) the voltage will actually be higher than 12 V. If there is a heavy load the voltage will drop. A good power supply tries to keep the voltage constant under a wide variety of conditions. It does this by using a Regulator.

The Bipolar Transistor

How it works

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There are two types of semi-conducting material in a transistor: N-Type and P-Type and they are arranged like a sandwich. The possible combinations of this sandwich are PNP (where a very thin N-Type layer is surrounded by P-Type layers) or NPN (where the very thin layer in the middle is P-Type).

Typically the majority of the current flow is in one end and out the other, with the middle section acting like a control on the current flow. One of the ends is called the EMITTER and the other end is called the COLLECTOR The middle part which controls the current is called the BASE.

The Field Effect Transistor (FET)

How it works

A FET consists of a piece of semi-conducting material (either P-Type or N-Type) which has a section in the middle which is of the other type. The section in the middle does not actually go completely through the material and in some cases is even insulated from the main piece of material (as in a MOSFET).

The effect of this middle piece (called the GATE) is much like stepping on a garden hose. The water flows through the hose (in the case of the FET the electricity flows from the SOURCE to the DRAIN) and you can control how much current flows by how hard you step on the hose. In the FET the current is regulated by controlling the bias on the GATE and using the field-effects caused by the depletion layer around the FET to determine how much current can flow through the material. The big piece of semi-conducting material is called a channel.

The Vacuum Tube

How it works

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Around the turn of the 20th century inventors discovered that if a piece of metal were heated it was possible to dislodge some of the electrons from the metal. In fact, if you were to set up a voltage difference (say by using a battery) between a heated metal plate and another plate near by that an electrical current would flow between the heated plate and the one nearby.

This type of device was one of the first things used to change A.C. voltage into D.C. But there is more!

If a charged wire mesh is inserted between the two plates, the current flowing between the plates can be controlled. This setup became the basis for the Vacuum Tube.

In a Vacuum Tube a piece of metal, called the CATHODE is heated by the FILAMENT. Electrons dislodged from the CATHODE flow towards the PLATE. A wire mesh used to control the amount of current allowed to flow is placed between the CATHODE and the PLATE. This is called the GRID

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