WEBVTT NOTE What Each Box in the Station Does 1 00:00:00.000 --> 00:00:03.760 Two receiver qualities that are not the same. 2 00:00:03.760 --> 00:00:11.760 Question. Which term describes the ability of a receiver to detect the presence of a signal? 3 00:00:12.660 --> 00:00:15.500 Answer. Sensitivity. 4 00:00:16.100 --> 00:00:24.380 Question. Which term describes the ability of a receiver to discriminate between multiple signals? 5 00:00:25.280 --> 00:00:27.908 Answer. Selectivity. 6 00:00:28.508 --> 00:00:43.593 Sensitivity is how weak a signal it can hear at all. Selectivity is how well it separates that signal from its neighbours. They are independent, and a receiver can be excellent at one and poor at the other. 7 00:00:43.593 --> 00:01:00.508 A very sensitive receiver with poor selectivity hears everything at once, which is the actual failure mode of cheap wideband receivers, and why adding a preamplifier to a crowded band often makes reception worse rather than better. 8 00:01:00.508 --> 00:01:12.059 The blocks inside. Block, Transceiver; Function, combines a receiver and transmitter. Block, Oscillator; Function, generates a signal at a specific frequency. 9 00:01:12.059 --> 00:01:21.929 Block, VFO; Function, sets the receive and transmit frequency. Block, Mixer; Function, converts a signal from one frequency to another. 10 00:01:21.929 --> 00:01:34.138 Block, Modulator; Function, combines speech with an RF carrier, the process is modulation. Block, RF power amplifier; Function, increases the transmitted output power. 11 00:01:34.138 --> 00:01:44.227 Block, Transverter; Function, converts the RF input and output of a transceiver to another band. The mixer is the one worth understanding. 12 00:01:44.227 --> 00:02:02.650 Every superheterodyne receiver works by mixing the incoming signal with a local oscillator to shift it to a fixed intermediate frequency, where the filtering and amplification happen at one convenient frequency instead of across the whole tuning range. 13 00:02:02.650 --> 00:02:08.572 It is the trick that made tunable radio practical, and it is a hundred years old. 14 00:02:08.572 --> 00:02:19.684 A transverter is the same trick applied to a whole station: feed it a signal on a band your radio covers, and it converts to a band your radio does not. 15 00:02:19.684 --> 00:02:27.068 It is how a 2 metre radio operates on 23 centimetres or on 6 metres. Controls with specific meanings. 16 00:02:27.068 --> 00:02:33.016 Question. What is the function of a transceiver's PTT input? 17 00:02:33.916 --> 00:02:40.956 Answer. Switches transceiver from receive to transmit when grounded. 18 00:02:41.556 --> 00:02:48.212 Grounded, not powered, the convention across essentially all amateur equipment. 19 00:02:48.212 --> 00:02:58.994 Question. What is the function of the switch which selects either SSB or CW-FM on some VHF power amplifiers? 20 00:02:59.894 --> 00:03:06.054 Answer. Set the amplifier for proper operation in the selected mode. 21 00:03:06.654 --> 00:03:26.468 The two mode families make very different demands. SSB is intermittent with high peaks; CW and FM are continuous carrier. The switch adjusts bias and, on many amplifiers, the transmit-receive switching delay to match. 22 00:03:26.468 --> 00:03:28.294 Adding an amplifier. 23 00:03:28.294 --> 00:03:35.922 Question. What can be added to the output of a transceiver to increase the transmitted output power? 24 00:03:36.822 --> 00:03:40.820 Answer. An RF power amplifier. 25 00:03:41.420 --> 00:03:56.204 Worth pairing with the decibel arithmetic from the foundations track: going from 50 W to 500 W is 10 dB, a genuine improvement, and about one and a half S-units at the far end. 26 00:03:56.204 --> 00:04:14.600 Fixing a lossy feed line and putting up a better antenna often buys more, and unlike an amplifier it helps on receive too. Check yourself. Your receiver hears a weak station but a strong nearby signal makes it unusable. 27 00:04:14.600 --> 00:04:26.780 Which quality is lacking? What does a mixer do, and why does a receiver need one? You want to operate 6 metres with a 2 metre radio. What device? 28 00:04:32.780 --> 00:04:41.342 Selectivity, the ability to discriminate between multiple signals. Sensitivity is fine; it heard the weak one. 29 00:04:41.342 --> 00:04:55.820 It converts a signal from one frequency to another, so filtering and amplification can happen at one fixed intermediate frequency instead of across the whole tuning range. A transverter.