WEBVTT NOTE Speech Processors, S Meters, and Band Edges 1 00:00:00.000 --> 00:00:02.000 Speech processing. 2 00:00:02.000 --> 00:00:07.640 Question. What is the purpose of a speech processor in a transceiver? 3 00:00:08.540 --> 00:00:14.420 Answer. Increase the apparent loudness of transmitted voice signals. 4 00:00:15.020 --> 00:00:21.739 Question. How does a speech processor affect a single sideband phone signal? 5 00:00:22.639 --> 00:00:26.516 Answer. It increases average power. 6 00:00:27.116 --> 00:00:38.583 Speech has a high peak-to-average ratio: the peaks set your PEP while the average power, which determines how far you get, is much lower. 7 00:00:38.583 --> 00:00:52.560 A speech processor compresses that ratio, raising average power without raising the peaks. Note apparent loudness. Your PEP is unchanged, which is what the FCC limits. 8 00:00:52.560 --> 00:00:56.996 What changes is how much of the time you are near it. 9 00:00:56.996 --> 00:01:17.055 Question. What is the effect of an incorrectly adjusted speech processor? A. Distorted speech. B. Excess intermodulation products. C. Excessive background noise. D. All these choices are correct. 10 00:01:17.955 --> 00:01:21.475 Answer. All these choices are correct. 11 00:01:22.075 --> 00:01:37.835 Overdo it and you get all three: the compression distorts, the extra gain brings up room noise, and the raised average level pushes the transmitter beyond linear. Reading an S meter. 12 00:01:37.835 --> 00:01:41.776 Question. What does an S meter measure? 13 00:01:42.676 --> 00:01:46.236 Answer. Received signal strength. 14 00:01:46.836 --> 00:01:51.956 The scale is logarithmic, and the exam wants the numbers. 15 00:01:51.956 --> 00:01:59.522 Question. How much change in signal strength is typically represented by one S unit? 16 00:02:00.422 --> 00:02:03.622 Answer. 6 dB. 17 00:02:04.222 --> 00:02:10.422 Six decibels per S unit, a factor of four in power. So: 18 00:02:10.422 --> 00:02:23.062 Question. How much must the power output of a transmitter be raised to change the S meter reading on a distant receiver from S8 to S9? 19 00:02:23.962 --> 00:02:27.762 Answer. Approximately 4 times. 20 00:02:28.362 --> 00:02:40.988 Four times the power for one S unit. That is a sobering exchange rate, and it is the strongest argument for spending money on antennas rather than amplifiers. 21 00:02:40.988 --> 00:02:53.948 Question. How does a signal that reads 20 dB over S9 compare to one that reads S9 on a receiver, assuming a properly calibrated S meter? 22 00:02:54.848 --> 00:02:59.108 Answer. It is 100 times more powerful. 23 00:02:59.708 --> 00:03:05.540 Twenty decibels is a factor of 100, straight from the decibel anchors. 24 00:03:05.540 --> 00:03:20.786 Note that "20 over" is a decibel figure, not S units, above S9 the scale switches from S units to decibels over S9, because there are only nine S units. Where your signal actually is. 25 00:03:20.786 --> 00:03:32.117 This is the practical band-edge material, and it is worth working through slowly because the exam asks it twice with opposite sidebands. 26 00:03:32.117 --> 00:03:49.030 An SSB signal occupies about 3 kHz, and the displayed carrier frequency is one edge of it, not the middle. Which edge depends on the sideband: USB: the signal extends upward from the displayed frequency. 27 00:03:49.030 --> 00:03:54.195 LSB: the signal extends downward from the displayed frequency. 28 00:03:54.195 --> 00:04:08.595 Question. What frequency range is occupied by a 3 kHz LSB signal when the displayed carrier frequency is set to 7.178 MHz? 29 00:04:09.495 --> 00:04:17.550 Answer. 7.175 MHz to 7.178 MHz. 30 00:04:18.150 --> 00:04:23.814 Lower sideband, so 3 kHz below the displayed frequency. 31 00:04:23.814 --> 00:04:36.428 Question. What frequency range is occupied by a 3 kHz USB signal with the displayed carrier frequency set to 14.347 MHz? 32 00:04:37.328 --> 00:04:45.448 Answer. 14.347 MHz to 14.350 MHz. 33 00:04:46.048 --> 00:05:04.768 Upper sideband, so 3 kHz above. And notice that this one lands exactly on 14.350, the top edge of the 20 metre band. One kilohertz higher on the dial and you are transmitting outside it. The 3 kHz rule. 34 00:05:04.768 --> 00:05:16.448 Question. How close to the lower edge of a band's phone segment should your displayed carrier frequency be when using 3 kHz wide LSB? 35 00:05:17.348 --> 00:05:23.228 Answer. At least 3 kHz above the edge of the segment. 36 00:05:23.828 --> 00:05:35.228 Question. How close to the upper edge of a band's phone segment should your displayed carrier frequency be when using 3 kHz wide USB? 37 00:05:36.128 --> 00:05:41.541 Answer. At least 3 kHz below the edge of the band. 38 00:05:42.141 --> 00:05:59.861 At least 3 kHz from either edge, whichever sideband you are using. The rule is symmetric even though the reason is not: near the lower edge it is LSB that gets you into trouble, and near the upper edge it is USB. 39 00:05:59.861 --> 00:06:16.244 Setting 3 kHz clear of both edges means you are legal regardless of which sideband is in use, which is why it is the rule worth carrying rather than the reasoning. Check yourself. A station is S7. 40 00:06:16.244 --> 00:06:30.035 What power increase would make them S9 at the same receiver? You are on 40 metre LSB with the dial at 7.176 MHz. Where is your signal, and is it legal for a General? 41 00:06:30.035 --> 00:06:35.301 What does "10 dB over S9" mean in power terms compared with S9? 42 00:06:41.301 --> 00:07:06.661 Two S units is 12 dB, a factor of about 16 times the power. (Four times per S unit, twice.). 7.173 to 7.176 MHz, which is below 7.175, inside the Extra-only segment. Not legal for a General. Move up. Ten times the power.