WEBVTT NOTE Mobile, Portable, and Off-Grid Power 1 00:00:00.000 --> 00:00:03.440 Powering a mobile HF radio. 2 00:00:03.440 --> 00:00:13.920 Question. Which of the following direct, fused power connections would be the best for a 100-watt HF mobile installation? 3 00:00:14.820 --> 00:00:19.565 Answer. To the battery using heavy-gauge wire. 4 00:00:20.165 --> 00:00:30.409 Question. Why should DC power for a 100-watt HF transceiver not be supplied by a vehicle's auxiliary power socket? 5 00:00:31.309 --> 00:00:37.561 Answer. The socket's wiring may be inadequate for the current drawn by the transceiver. 6 00:00:38.161 --> 00:00:42.507 A 100 W HF radio draws around 20 amperes on transmit. 7 00:00:42.507 --> 00:00:57.594 An accessory socket is typically wired for 10 to 15 A through thin wire and a long path, so at transmit current the voltage sags (distorted audio, reduced output) and the wiring heats. 8 00:00:57.594 --> 00:01:12.681 Direct to the battery, heavy gauge, fused close to the positive terminal. The fuse is not optional: an unfused heavy wire from a battery is a welding cable. The mobile antenna problem. 9 00:01:12.681 --> 00:01:18.921 Question. Which of the following most limits an HF mobile installation? 10 00:01:19.821 --> 00:01:24.863 Answer. Efficiency of the electrically short antenna. 11 00:01:25.463 --> 00:01:34.569 Not the radio, not the power, not the noise. A quarter wave on 40 metres is 33 feet; a mobile whip is 8. 12 00:01:34.569 --> 00:01:47.703 Loading it to resonance works, and the radiation resistance drops to a few ohms while the losses do not, so most of your power warms the loading coil. 13 00:01:47.703 --> 00:01:56.623 Question. What is one disadvantage of using a shortened mobile antenna as opposed to a full-size antenna? 14 00:01:57.523 --> 00:02:02.323 Answer. Operating bandwidth may be very limited. 15 00:02:02.923 --> 00:02:15.796 The second consequence of the same physics: a heavily loaded antenna is a high-Q circuit, so it is resonant over a narrow range and needs retuning after a small frequency change. 16 00:02:15.796 --> 00:02:25.849 This is exactly what the screwdriver antenna from the antennas module exists to solve. Two accessories address the length problem directly: 17 00:02:25.849 --> 00:02:32.169 Question. What is the purpose of a capacitance hat on a mobile antenna? 18 00:02:33.069 --> 00:02:38.286 Answer. To electrically lengthen a physically short antenna. 19 00:02:38.886 --> 00:02:56.030 A disc or set of spokes at the top adds capacitance to the antenna's far end, which shifts resonance down as if the antenna were longer, so less loading inductance is needed, and less power is lost in it. 20 00:02:56.030 --> 00:03:02.754 Question. What is the purpose of a corona ball on an HF mobile antenna? 21 00:03:03.654 --> 00:03:10.055 Answer. To reduce RF voltage discharge from the tip of the antenna while transmitting. 22 00:03:10.655 --> 00:03:20.980 The voltage at the tip of a loaded antenna is very high, that is where the current is minimum and the voltage maximum. 23 00:03:20.980 --> 00:03:38.217 A sharp point concentrates the field enough to ionise air, producing corona: a visible glow, an audible hiss, RF noise, and lost power. A rounded ball spreads the field and stops it. Vehicle noise. 24 00:03:38.217 --> 00:03:57.430 Question. Which of the following may cause receive interference to an HF transceiver installed in a vehicle? A. The battery charging system. B. The fuel delivery system. C. The control computers. D. 25 00:03:57.430 --> 00:04:00.341 All these choices are correct. 26 00:04:01.241 --> 00:04:04.761 Answer. All these choices are correct. 27 00:04:05.361 --> 00:04:09.598 Modern vehicles are full of switching electronics. 28 00:04:09.598 --> 00:04:24.260 Fixes, in order of usual effectiveness: get the antenna away from the noise sources and off the body, ferrite chokes on the offending harnesses, and filtering at the source. 29 00:04:24.260 --> 00:04:31.294 The noise blanker helps with the pulsed sources and not with the rest. Solar power. 30 00:04:31.294 --> 00:04:38.873 Question. In what configuration are the individual cells in a solar panel connected together? 31 00:04:39.773 --> 00:04:42.893 Answer. Series-parallel. 32 00:04:43.493 --> 00:04:51.967 Question. What is the approximate open-circuit voltage from a fully illuminated silicon photovoltaic cell? 33 00:04:52.867 --> 00:04:57.307 Answer. 0.5 VDC. 34 00:04:57.907 --> 00:05:11.547 Half a volt per cell, so a nominal 12 V panel is around 36 cells in series, and parallel strings for current. That is why panel voltages come in the values they do. 35 00:05:11.547 --> 00:05:21.787 Question. Why should a series diode be connected between a solar panel and a storage battery that is being charged by the panel? 36 00:05:22.687 --> 00:05:31.751 Answer. To prevent discharge of the battery through the panel during times of low or no illumination. 37 00:05:32.351 --> 00:05:47.551 A dark panel is a load, not a source. The blocking diode makes the connection one-way. Note that it costs you its forward drop, a reason to use a Schottky, from the semiconductors lesson. 38 00:05:47.551 --> 00:05:55.820 Question. What precaution should be taken when connecting a solar panel to a lithium iron phosphate battery? 39 00:05:56.720 --> 00:06:01.734 Answer. The solar panel must have a charge controller. 40 00:06:02.334 --> 00:06:14.360 Not optional and not a refinement. Lithium chemistries need charge terminated correctly, and a panel connected directly will overcharge the cells. 41 00:06:14.360 --> 00:06:30.918 LiFePO 4 is the safest of the lithium chemistries and still needs a controller, and a modern MPPT controller also extracts substantially more energy from the same panel. The portable-station checklist. 42 00:06:30.918 --> 00:06:47.969 [ ] Power direct to the battery, heavy gauge, fused at the positive terminal. [ ] Antenna as tall and as clear of the body as you can manage. [ ] Capacitance hat or a screwdriver antenna if you change bands. 43 00:06:47.969 --> 00:07:01.478 [ ] Corona ball on the tip. [ ] Ferrites on any harness that turns out to be noisy. [ ] Solar: blocking diode and, for lithium, a charge controller. Check yourself. 44 00:07:01.478 --> 00:07:18.694 Why not run a 100 W HF radio from the cigarette-lighter socket? Your mobile whip tunes perfectly at 7.150 MHz and badly at 7.250. Fault? You connect a 100 W panel straight to a LiFePO 4 battery. What is wrong? 45 00:07:24.694 --> 00:07:37.329 The socket's wiring is inadequate for the roughly 20 A the radio draws. Voltage sags and the wiring heats. Run direct to the battery with heavy fused wire. 46 00:07:37.329 --> 00:07:54.122 Not a fault, a shortened, heavily loaded antenna has very limited bandwidth. Retune it, or fit a remotely tunable antenna. It needs a charge controller. A panel connected directly will overcharge the cells.