WEBVTT NOTE Connecting a Station 1 00:00:00.000 --> 00:00:02.322 Sizing the power supply. 2 00:00:02.322 --> 00:00:12.082 Question. Which of the following is an appropriate power supply rating for a typical 50-watt output mobile FM transceiver? 3 00:00:12.982 --> 00:00:18.102 Answer. 13.8 volts at 12 amperes. 4 00:00:18.702 --> 00:00:36.122 Not 50 W of supply. A radio putting out 50 W of RF at maybe 40% efficiency draws well over 100 W from the supply, and 13.8 V times 12 A = 166 W. That headroom is the point. 5 00:00:36.122 --> 00:00:48.984 The general recipe, from the power law: estimate the DC input as roughly twice the RF output, divide by 13.8 V, and add margin. 6 00:00:48.984 --> 00:01:06.100 Undersize the supply and the voltage sags on transmit, which shows up as distorted audio and reduced output, symptoms people spend weeks chasing in the radio. DC wiring. 7 00:01:06.100 --> 00:01:14.320 Question. Why are short, heavy-gauge wires used for a transceiver's DC power connection? 8 00:01:15.220 --> 00:01:19.867 Answer. To minimize voltage drop when transmitting. 9 00:01:20.467 --> 00:01:37.787 Transmit current is tens of amperes, and every milliohm of wire resistance becomes a voltage drop at exactly the wrong moment. The radio sees less than 13.8 V, folds back its output, and distorts. In a vehicle: 10 00:01:37.787 --> 00:01:45.547 Question. Where should the negative power return of a mobile transceiver be connected in a vehicle? 11 00:01:46.447 --> 00:01:50.889 Answer. At the 12-volt battery chassis ground. 12 00:01:51.489 --> 00:02:07.933 Directly at the battery, not to a convenient bolt under the dashboard. Every intermediate joint adds resistance and noise; the alternator's electrical noise reaches your receiver through exactly those paths. 13 00:02:07.933 --> 00:02:14.288 For bonding at RF, the preferred conductor is flat copper strap. Not round wire. 14 00:02:14.288 --> 00:02:26.680 At radio frequencies, current flows in the surface of a conductor, the skin effect, so what matters is surface area and perimeter, not cross-sectional area. 15 00:02:26.680 --> 00:02:36.769 A flat strap has far more perimeter than a round wire of the same weight, and much lower inductance. Meters, and where they go. 16 00:02:36.769 --> 00:02:41.190 Question. Where should an RF power meter be installed? 17 00:02:42.090 --> 00:02:48.050 Answer. In the feed line, between the transmitter and antenna. 18 00:02:48.650 --> 00:02:59.918 In line, in the path, so it sees what is actually flowing. The same is true for an SWR meter, and for the same reason. 19 00:02:59.918 --> 00:03:07.398 Question. Which of the following should be considered when selecting an accessory SWR meter? 20 00:03:08.298 --> 00:03:14.565 Answer. The frequency and power level at which the measurements will be made. 21 00:03:15.165 --> 00:03:34.445 A meter built for HF at 100 W reads nonsense at 440 MHz, and one built for QRP will be destroyed by a legal-limit amplifier. Both specifications matter and both are printed on the meter. Battery endurance. 22 00:03:34.445 --> 00:03:41.125 Question. How can you determine the length of time that equipment can be powered from a battery? 23 00:03:42.025 --> 00:03:49.035 Answer. Divide the battery ampere-hour rating by the average current draw of the equipment. 24 00:03:49.635 --> 00:04:05.721 A 20 Ah battery running equipment that averages 2 A lasts about 10 hours. Note average, for a radio that is dominated by receive current, because transmit is a small fraction of the time. 25 00:04:05.721 --> 00:04:19.656 Sizing on transmit current alone gives a number several times too pessimistic. Connecting a computer. Digital modes need three signals between computer and radio: 26 00:04:19.656 --> 00:04:27.256 Question. What signals are used in a computer-radio interface for digital mode operation? 27 00:04:28.156 --> 00:04:34.820 Answer. Receive audio, transmit audio, and transmitter keying. 28 00:04:35.420 --> 00:04:40.900 Two audio paths and one control line. Concretely: 29 00:04:40.900 --> 00:04:50.460 Question. How are the audio input and output of a transceiver connected in a station configured to operate using FT8? 30 00:04:51.360 --> 00:04:58.872 Answer. To the audio output and input of a computer running FT8 software. 31 00:04:59.472 --> 00:05:14.142 Crossed over, the radio's output goes to the computer's input: computer "line in" to transceiver speaker connector, and computer line out to the radio's microphone or data input. 32 00:05:14.142 --> 00:05:18.592 The third signal, keying, tells the radio to transmit. 33 00:05:18.592 --> 00:05:24.540 Question. What is the function of a transceiver's PTT input? 34 00:05:25.440 --> 00:05:32.480 Answer. Switches transceiver from receive to transmit when grounded. 35 00:05:33.080 --> 00:05:44.450 Grounded, not powered. That is the convention on almost every radio, and it is why a simple transistor or relay in the interface is enough. 36 00:05:44.450 --> 00:06:00.400 Modern radios often carry all three over a single USB connection, with the sound card and serial port inside the radio. The signals are the same; the wiring is simply hidden. Hotspots and keyers. 37 00:06:00.400 --> 00:06:07.334 Question. What function does a digital mode hotspot perform for nearby transceivers? 38 00:06:08.234 --> 00:06:13.576 Answer. Communication with a digital voice or data network. 39 00:06:14.176 --> 00:06:32.136 A very low power transceiver plus an internet connection, giving a handheld access to a DMR, D-STAR, or similar network without a local repeater. A hotspot on a desk covers a house and connects it to the world. 40 00:06:32.136 --> 00:06:36.360 Question. What is an electronic keyer? 41 00:06:37.260 --> 00:06:43.523 Answer. A device that assists in manual sending of Morse code. 42 00:06:44.123 --> 00:06:58.984 It generates properly timed dits and dahs from a paddle, so the operator supplies the rhythm of the characters and the electronics supply the timing. Check yourself. 43 00:06:58.984 --> 00:07:13.936 Your radio's output drops and audio distorts, but only on transmit and only in the car. What do you check first? Why flat strap rather than round wire for RF bonding? 44 00:07:13.936 --> 00:07:23.483 A 12 Ah battery, a radio drawing 0.8 A on receive and 9 A on transmit, mostly listening. Roughly how long? 45 00:07:29.483 --> 00:07:42.497 The DC connection, short, heavy-gauge wire with the negative return at the battery chassis ground. Voltage drop under transmit current is the classic cause. 46 00:07:42.497 --> 00:08:00.184 RF flows in the surface of a conductor, so perimeter and surface area matter more than cross-section, and strap has far lower inductance. Average current is close to receive current, so roughly 12 / 1 ≈ 12 hours. 47 00:08:00.184 --> 00:08:08.443 Sizing on the 9 A transmit figure would suggest 1.3 hours, which is wrong by an order of magnitude.