HamSandwich

Repeaters, simplex, and questionable antenna choices.

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G4D

AMATEUR RADIO PRACTICES

- Speech processors; S meters; sideband operation near band edges

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G4D011 of 11

What is the purpose of a speech processor in a transceiver?

Why SSB output power is limited by peak envelope power, but intelligibility depends on average power. A speech processor compresses or clips the audio so quieter syllables are brought up closer to the peaks, raising the average-to-peak ratio and putting more talk power on the air. The result is a signal that sounds louder and punches through noise better at the receiving end, without exceeding the transmitter's PEP limit.
Watch out The choice about preventing distortion has it backwards: processing deliberately adds some distortion (clipping/compression), and overdoing it makes a signal splattery and hard to copy. Boosting bass actually hurts SSB intelligibility, since communication audio favors the mid and higher voice frequencies.
Processor = more average power under the same PEP roof: louder talk power, not cleaner audio.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
G4D022 of 11

How does a speech processor affect a single sideband phone signal?

Why An SSB transmitter's peak envelope power is fixed by the PA and legal limit, so the only way to get more "talk power" is to raise the average power relative to that peak. A speech processor compresses or clips the audio, reducing the peak-to-average ratio of speech so more of the time the transmitter runs near full output. That raises average power and improves readability at the far end, especially for voices with a low natural average-to-peak ratio.
Watch out The choice about increasing peak power is tempting, but PEP stays the same, set by the transmitter and the 1500 W limit; only the average rises. Overdriving a processor actually adds distortion and splatter rather than reducing harmonic or intermodulation distortion.
Peak is capped, so processing fills in the valleys: same PEP, higher average = more talk power.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
G4D033 of 11

What is the effect of an incorrectly adjusted speech processor?

Why A speech processor raises average talk power by compressing or clipping the audio, but overdoing it hurts all three ways at once. Too much compression flattens and clips the waveform, which is audible distortion; that clipping generates harmonics and intermodulation products in the audio that translate into splatter and wide, adjacent-channel signals; and because compression raises the gain during pauses, it also pulls up shack noise, fans, and background sounds that would otherwise be inaudible. The goal is a few dB of compression with ALC just barely moving, not maximum processing.
Watch out Each single-effect choice is true but incomplete, so picking only distorted speech or only intermodulation misses the other real consequences of over-processing.
Over-processing: distorted, splattery, and noisy. If one processor symptom is listed, expect all of them to be.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
G4D044 of 11

What does an S meter measure?

Why An S meter is a receiver indicator calibrated to show the relative strength of the incoming signal, normally driven from the receiver's AGC voltage. The scale runs S1 through S9, and above S9 it is marked in decibels over S9. By convention on HF, S9 corresponds to 50 microvolts at the antenna terminals into 50 ohms, and one S unit is nominally 6 dB, so a change of one S unit means about a four-fold change in received power.
Watch out Transmitter power output is read on a wattmeter or power meter, not an S meter, which is a receiving-side instrument; impedance needs an antenna analyzer or bridge, and carrier suppression is a transmitter SSB spec measured on a spectrum analyzer.
S is for Signal strength, on the receive side. S9 = 50 microvolts, 1 S unit = 6 dB.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
G4D055 of 11

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?

Why S meter readings above S9 are given in decibels, and 20 dB is a power ratio of 10^(20/10) = 10^2 = 100. So a signal 20 dB over S9 delivers 100 times the power of an S9 signal (it is also 10 times the voltage, since voltage ratio is 10^(20/20)).
Watch out The choice saying 20 times more powerful confuses the decibel number with the power ratio itself; decibels are logarithmic, so 20 dB is not 20 times. Ten times power would be 10 dB, not 20 dB.
Every 10 dB multiplies power by 10: 10 dB = 10x, 20 dB = 100x, 30 dB = 1000x.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
G4D066 of 11

How much change in signal strength is typically represented by one S unit?

Why By convention an S meter is calibrated so that each S unit represents a 6 dB change in received signal strength, which is a factor of about 2 in voltage or 4 in power. The reference point is S9, defined on HF as 50 microvolts at the receiver's 50 ohm input; above S9 the scale is marked in dB over S9 rather than S units. So a report going from S5 to S7 means the signal came up roughly 12 dB.
Watch out The 12 dB choice is what two S units represent, not one, and the larger figures do not correspond to any standard S meter step.
One S unit = 6 dB = double the voltage. S9 = 50 microvolts.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
G4D077 of 11

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?

Why By convention one S unit equals 6 dB of signal strength change. In power terms, 6 dB is a factor of about 4 (3 dB doubles power, another 3 dB doubles it again), so going from S8 to S9 on the far end requires roughly four times the transmitter output.
Watch out Doubling power is only a 3 dB increase, which is just half an S unit, so the choice that says approximately 2 times falls short; eight times would be about 9 dB, or a unit and a half.
1 S unit = 6 dB = 4x power. Two S units would take 16x.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
G4D088 of 11

What frequency range is occupied by a 3 kHz LSB signal when the displayed carrier frequency is set to 7.178 MHz?

Why On lower sideband the transmitted energy sits entirely below the suppressed carrier frequency shown on the display. A 3 kHz wide signal therefore extends from 7.178 MHz minus 3 kHz up to the displayed frequency, so it occupies 7.175 to 7.178 MHz. This matters near band edges: on LSB you must stay at least 3 kHz above the lower edge, and on USB at least 3 kHz below the upper edge.
Watch out The range running up to 7.181 MHz is what a USB signal on the same dial reading would occupy, since upper sideband puts the energy above the carrier frequency.
LSB goes down, USB goes up. Subtract or add 3 kHz to the dial reading.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
G4D099 of 11

What frequency range is occupied by a 3 kHz USB signal with the displayed carrier frequency set to 14.347 MHz?

Why In upper sideband the transmitter suppresses the carrier and transmits only the sideband above the displayed carrier (dial) frequency. A 3 kHz wide audio passband therefore puts energy from the dial frequency up to 3 kHz higher: 14.347 MHz + 0.003 MHz = 14.350 MHz. That happens to land exactly on the top edge of the 20 meter band, so 14.347 MHz is the highest dial setting you can legally use for a 3 kHz USB signal there.
Watch out The range running 3 kHz below the dial frequency describes an LSB signal, where the emitted energy falls under the displayed carrier frequency instead of above it.
USB goes Up, LSB goes Lower. Dial + 3 kHz on USB, dial - 3 kHz on LSB; keep the far edge inside the band.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
G4D1010 of 11

How close to the lower edge of a band's phone segment should your displayed carrier frequency be when using 3 kHz wide LSB?

Why With lower sideband, all your transmitted energy sits below the displayed carrier (suppressed carrier) frequency, spreading down about 3 kHz for a typical voice signal. To keep every part of that signal inside the band or segment, the displayed frequency must be at least 3 kHz above the lower edge. Remember that FCC rules hold you responsible for your entire emitted bandwidth, not just the dial reading.
Watch out Setting the dial below the edge, or only 1 kHz above it, puts part or all of the LSB energy outside the authorized segment, which is a violation even though the displayed number looks close to legal.
LSB talks downward: stay 3 kHz up from the bottom edge. USB talks upward: stay 3 kHz down from the top edge.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
G4D1111 of 11

How close to the upper edge of a band's phone segment should your displayed carrier frequency be when using 3 kHz wide USB?

Why With upper sideband, your transmitted energy sits above the displayed carrier frequency, so a 3 kHz wide USB signal occupies roughly carrier to carrier+3 kHz. To keep every bit of that occupied bandwidth inside the phone segment, the displayed carrier must sit at least 3 kHz below the upper edge. You are responsible for the whole emission, not just the dial reading, under the band edge requirements of Part 97.
Watch out Putting the carrier 1 kHz below the edge only works for a signal 1 kHz wide, so a normal 3 kHz voice signal would spill 2 kHz outside the segment; placing the carrier above the edge puts the whole signal out of band.
USB builds upward: back off the dial by your full bandwidth, 3 kHz wide means 3 kHz below the top edge.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
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