Lesson 9: Base Stations Preparation for Amateur Radio Technician Class Exam Copyright © Winters2 2004 Version 1.0 Topics ¾Home Stations ¾Basic Station Layout ¾RTTY and Data Communications ¾Station Accessories ¾Wavelengths ¾Feed Lines ¾Impedance-matching & balancing ¾Exam Questions for this section Copyright © Winters2 2004 Lesson 2: How Radio Works - 1 Version 1.0 Reading ¾Chapter 8 – 8.1-8.19 Copyright © Winters2 2004 Lesson 2: How Radio Works - 2 Version 1.0 Home Station – Your Shack ¾Traditionally, the place where we set up our radio station is the “shack” If you just have an HT, your “shack” might be where you charge your radio! You might also have a larger antenna at home to get better range from your HT. Copyright © Winters2 2004 Lesson 2: How Radio Works - 3 Version 1.0 Home Station – Your Shack ¾Your shack should enable you to lock up your gear to prevent unlicensed people from using it when you are not present Many hams have their HTs with them at all times, so don’t have to worry about locking them! If your shack is in an area where the radio sounds might bother others, you can get a headset with microphone to use with your radio Copyright © Winters2 2004 Lesson 2: How Radio Works - 4 Version 1.0 Base Station Layout ¾Any ham radio operator with any license can build and operate their own radio station. In this section we look at the parts of a station that you need to operate Most of these components are built into your HT radios Copyright © Winters2 2004 Lesson 2: How Radio Works - 5 Version 1.0 Base Station Layout Antenna Feed Line Transmitter TR Switch Receiver Power Supply Copyright © Winters2 2004 Lesson 2: How Radio Works - 6 Version 1.0 Transmitters ¾A transmitter produces RF signals ¾The signal from a transmitter is called an RF carrier ¾Transmitters have two stages: Oscillator Power amplifier Copyright © Winters2 2004 Lesson 2: How Radio Works - 7 Version 1.0 Transmitters - CW ¾ To transmit Morse Code the RF signal from a transmitter is turned on and off in a pattern This is a kind of modulation of the RF signal ¾ The frequency you transmit on can be set in two different ways Crystal oscillator Variable-frequency oscillator (VFO) ¾ To prevent AC hum from interfering by modulating the CW transmission, be sure the power supply is filtered Copyright © Winters2 2004 Lesson 2: How Radio Works - 8 Version 1.0 Transmitters - CW Box 1 in the diagram below represents the oscillator, either crystal or VFO Copyright © Winters2 2004 Lesson 2: How Radio Works - 9 Version 1.0 Transmitters - FM ¾ To transmit voice, the RF signal from a transmitter is modified when a circuit called a modulator is used to add voice content to the RF carrier ¾ FM transmission is popular because it is less affected by interference from static-type electrical noise than the AM modes ¾ The signal can be modulated by either frequency or phase These are so closely related, that practically they will appear to be the same – only the circuitry varies Copyright © Winters2 2004 Lesson 2: How Radio Works - 10 Version 1.0 Transmitters - FM ¾The frequency from the oscillator is modulated by a circuit called a reactance modulator, which reacts to the rise and fall of your voice to raise and lower the frequency that is transmitted Copyright © Winters2 2004 Lesson 2: How Radio Works - 11 Version 1.0 Transmitters - FM Box 1 in the diagram below represents the reactance modulator Copyright © Winters2 2004 Lesson 2: How Radio Works - 12 Version 1.0 Transmitters - FM ¾ The voice signal from the microphone is rather weak, so it is boosted by the audio amplifier If the audio amplifier isn’t working, the signal from the microphone will be too weak to modulate the signal ¾ The clipper/filter sets the amplitude of the signal If the clipper/filter is not doing its job correctly, the signal can be over deviated and interfere with transmissions on nearby channels If someone tells you that your radio is over-deviating, try talking software or holding the microphone further away Copyright © Winters2 2004 Lesson 2: How Radio Works - 13 Version 1.0 Receivers ¾A receiver converts RF energy into an audio-frequency signal ¾The heart of the receiver is the detector A detector compares an unmodulated model to an incoming signal to get information Detectors are particular to types of modulation, such as AM, FM, or phase Copyright © Winters2 2004 Lesson 2: How Radio Works - 14 Version 1.0 Receivers – direct conversion ¾A tuned radio frequency receiver allows you to select the frequencies you will receive ¾A direct-conversion receiver uses a mixer to combine an incoming RF signal with a signal from a VFO to convert the signal directly to audio Copyright © Winters2 2004 Lesson 2: How Radio Works - 15 Version 1.0 Receivers - Superheterodyne ¾ Like a direct-conversion receiver, the superheterodyne receiver uses a mixer to combine an incoming RF signal with a signal from a VFO But instead of converting the signal directly to audio, the signal is converted instead to an intermediate frequency (IF) This intermediate frequency is amplified and sent to another circuit called a product detector The product detector mixes the signal with another signal from a beat frequency oscillator to produce an audio signal Some radio receivers have several IF filters of different bandwidths because some emission types need a wider bandwidth than others to be received properly Copyright © Winters2 2004 Lesson 2: How Radio Works - 16 Version 1.0 Receivers - Superheterodyne Box 1 in the diagram below represents the product detector. This receiver will work with SSB and CW. Copyright © Winters2 2004 Lesson 2: How Radio Works - 17 Version 1.0 Receivers - Superheterodyne ¾ To avoid the incoming sound from getting too loud and hurting your ears, most commercial receivers include automatic gain control ¾ You can use an S meter connected across the automatic gain control line to show relative signal strength ¾ To determine if your radio is properly calibrated for frequency, you can tune it in to the NIST frequency standard stations WWV or WWVH Copyright © Winters2 2004 Lesson 2: How Radio Works - 18 Version 1.0 Receivers - FM ¾An FM superheterodyne repeater adds more stages It has a different kind of detector called a frequency discriminator • With no frequency discriminator, you will have no audio output It also will usually include squelch circuitry • This mutes the noise when an FM carrier signal is not present • Tune the squelch just until noise is silenced, but you can still hear transmissions Copyright © Winters2 2004 Lesson 2: How Radio Works - 19 Version 1.0 Receivers - FM Box 1 in the diagram below represents the Frequency Discriminator. Copyright © Winters2 2004 Lesson 2: How Radio Works - 20 Version 1.0 Receivers - FM This FM receiver might be called a single-conversion superheterodyne receiver – it has one pass of IF filtering. The mixer can add or subtract the oscillator and IF frequencies – so this receiver can receive 168.4 MHz or 147.0 MHz. Copyright © Winters2 2004 Lesson 2: How Radio Works - 21 Version 1.0 Transceivers ¾A transceiver is a transmitter and a receiver put together in one box ¾A mobile transceiver is typically used in the car and is designed to run on 12V DC To use it at home either connect it to a 12V battery, or connect it to a power supply that converts 120V AC to 12V DC Copyright © Winters2 2004 Lesson 2: How Radio Works - 22 Version 1.0 Trouble-shooting ¾Your radio works fine in the car but not in the house: Check the power supply • Connect a voltmeter at the 12 V plug on the chassis of the radio when transmitting to see what current it is drawing • If there is no voltage, check the fuses ¾You hear a whine or clicks when running the radio using DC Filter the power lines for DC as well as RF Copyright © Winters2 2004 Lesson 2: How Radio Works - 23 Version 1.0 RTTY & Data Communications ¾These are forms of digital communications, often involving direct transfer of information between computers Copyright © Winters2 2004 Lesson 2: How Radio Works - 24 Version 1.0 RTTY ¾Radioteletype You connect the transceiver to a modem that is connected to either a computer or teleprinter Data received through the transceiver is output on the teleprinter or computer In the VHF/UHF bands, a common method of transmitting RTTY is to modulate a conventional FM transmitter with a modem Copyright © Winters2 2004 Lesson 2: How Radio Works - 25 Version 1.0 Packet ¾ Packet uses a terminal node controller (TNC) in place of a modem The sending TNC breaks the data into chunks, called packets, to send information to another TNC A receiving TNC recombines the packets into a signal ¾ The transceiver is often a VHF or UHF FM transceiver with the squelch control set low enough to receive packets, but high enough to filter out noise that might be mistaken for data Copyright © Winters2 2004 Lesson 2: How Radio Works - 26 Version 1.0 Station Accessories ¾Antenna Switch ¾SWR Meter ¾Antenna Tuner ¾Telegraph Key (paddle or bug) ¾Microphone ¾Duplexer ¾Power amplifier Copyright © Winters2 2004 Lesson 2: How Radio Works - 27 Version 1.0 Antenna Switch ¾This connects one transceiver (or transmitter/receiver pair) to several antennas ¾The switch determines which antenna the radio is currently using ¾Many hams have a switch between an antenna and a dummy antenna Copyright © Winters2 2004 Lesson 2: How Radio Works - 28 Version 1.0 Antenna Switch Antenna Antenna Dummy Transceiver Switch Antenna Copyright © Winters2 2004 Lesson 2: How Radio Works - 29 Version 1.0 SWR Meter ¾This measures