G4: Amateur Radio Practices

Your radio's front panel is covered in knobs and buttons, and each one is a tool for a specific job. This group teaches you which tool fixes which problem on the receive side, and how to safely set up a transmitter that drives an external power amplifier.

Cleaning up what you hear: the receiver tools

When you tune across a band, you rarely hear just the one signal you want. There are whistles, hiss, crashes, and other voices crowding in. Modern radios give you several controls to dig your signal out of that mess. The trick is matching the right control to the right problem.

• Notch filter. Imagine a single annoying whistle, a steady tone, sitting on top of the voice you are trying to hear. A notch filter punches a narrow "notch" (a tiny gap) into the receiver right at that tone's pitch and removes it, leaving the voice. Its purpose is to reduce interference from carriers in the receiver passband. (A "carrier" is a steady unchanging tone; the "passband" is the slice of frequencies your receiver is currently letting through. So a carrier in the passband is exactly that steady whistle landing on your signal.)
• Noise blanker. Some noise comes in sharp, repeated pulses, think of the tick-tick-tick of a car ignition or an electric fence. A noise blanker deals with this by reducing receiver gain during a noise pulse. ("Gain" means how much the receiver amplifies; the blanker briefly turns the volume down for the split second each pulse arrives, so you hear a tiny gap instead of a loud tick.)
• Noise reduction. This is a different, software-style control that tries to smooth out general hiss. The catch: turn it up too far and it starts chewing on the wanted signal too. As you increase the noise-reduction level, received signals may become distorted. So use just enough, and back off if voices start sounding underwater.
• Receive attenuator. "Attenuate" means to weaken. Sometimes an incoming signal is so strong it overwhelms the receiver and everything turns to mush, this is called overload. A receive attenuator turns down the signal before it enters the radio, and its purpose is to prevent receiver overload from strong incoming signals. Counterintuitive but true: deliberately making a signal weaker can make it sound much cleaner.
• Reverse sideband on CW. When you copy Morse code (CW), you can usually flip which side of the signal you listen to. Doing so changes which nearby interfering signals land on top of you, so using the opposite or "reverse" sideband when receiving CW means it may be possible to reduce or eliminate interference from other signals. It is a free second try at a clearer copy.
• Dual VFO. A VFO ("variable frequency oscillator") is just the circuit that sets your operating frequency, basically the tuning dial. Having two of them lets you do a common and very useful trick: transmit on one frequency and listen on another. This is called "split" operation, handy when a rare station is listening a little away from where they transmit.

Driving an external amplifier safely

Many hams add an external power amplifier (often just called a "linear" or "amp"), a separate box that boosts your radio's output to a higher power. Several controls exist to make the radio and amp cooperate without damage or distortion.

• ALC (automatic level control). This is a feedback system that keeps you from feeding the amplifier too much. Its job is to prevent excessive drive. ("Drive" is the amount of signal your radio pushes into the amp; too much drive distorts the signal or harms the amp, so ALC automatically holds it back.)
• ALC and digital modes. There is one important exception. When you send AFSK data signals (a way of sending digital data as audio tones, "audio frequency-shift keying"), you should turn ALC off, because the ALC action distorts the signal. ALC is built to ride along with voice, and it mangles the steady tones that digital modes rely on. Set your audio level by hand instead.
• RF output delay (keying delay). When your radio tells an external amp "we are about to transmit," the amp needs a heartbeat to throw its internal relays. So the radio delays its RF output for a moment. The purpose is to allow time for the amplifier to switch the antenna between the transceiver and the amplifier output. Skip this delay and the relay switches while power is flowing, which arcs and wears out the contacts ("hot switching").

Tuning a vacuum-tube amplifier (TUNE and LOAD)

Some older or higher-power amplifiers use vacuum tubes and have two big knobs, usually marked TUNE and LOAD (LOAD is sometimes called COUPLING). You adjust them by watching the amplifier's plate current meter. (The "plate" is the main output element inside a tube; plate current is how much current the tube is drawing, shown on a meter.) Two facts the test wants:

• The correct setting of the TUNE control shows up as a pronounced dip in plate current. You rotate TUNE and watch the meter swing down to a clear low point, that dip is the sweet spot.
• The correct setting of the LOAD (COUPLING) control is the one that gives you the desired power output without exceeding the maximum allowable plate current. In plain words: load it up for good output, but never push the plate current past the limit in the manual.

One more handy control

• Electronic keyer. If you send Morse code, an electronic keyer does the automatic generation of dots and dashes for CW operation. You tap a paddle and the keyer produces perfectly timed, even dots and dashes for you.
• Antenna tuner. We will meet this again in G4B, but the purpose of an antenna tuner is to increase power transfer from the transmitter to the feed line. It does not actually "tune" the antenna out on the mast; it makes the radio see a load it likes, so more of your power flows out instead of bouncing back.

Every workbench needs the right instruments. This group is about knowing which tool measures what, so you reach for the correct one. We will cover the oscilloscope, the multimeter (analog and digital), the directional wattmeter, and the antenna analyzer.

The oscilloscope: seeing a signal's shape

An oscilloscope (or "scope") draws a picture of a signal's voltage over time on a screen, so you can literally see its shape. A few facts to know:

• An oscilloscope contains horizontal and vertical channel amplifiers. (These move the trace left-right and up-down to draw the waveform.) If a question describes an instrument with those two amplifiers, it is a scope.
• Its big advantage over a simple digital voltmeter is that complex waveforms can be measured. A voltmeter gives you a single number; a scope shows the whole wiggling shape, so you can spot distortion, ringing, or odd patterns.
• It is the best instrument for checking the keying waveform of a CW transmitter, you can see whether your Morse dots and dashes have nice clean edges or ugly spikes that cause "key clicks."
• When you use a scope to look at the RF envelope pattern of your transmitted signal (the overall shape of your output), you feed its vertical input with the attenuated RF output of the transmitter. ("Attenuated" means weakened first, you never connect full transmit power straight into the scope; you knock it down to a safe level.)

Multimeters: analog versus digital

A multimeter measures voltage, current, and resistance. It comes in two flavors. An analog one has a needle that swings across a printed scale; a digital one (a DMM) shows numbers on a display.

• A digital multimeter's advantage over an analog one is higher precision, it gives you exact numbers with no guessing where the needle points.
• But an analog multimeter is preferred when adjusting circuits for maximum or minimum values. Why? A swinging needle makes it easy to watch a reading climb to a peak or fall to a valley as you turn a knob. Watching numbers flicker on a digital screen is much harder for "peak it up" or "null it out" work.
• Why do voltmeters have high input impedance? Because it decreases the loading on the circuit being measured. ("Loading" means the meter accidentally drawing current and changing the very thing you are trying to read. A high-impedance meter sips almost no current, so it reads the true voltage without disturbing the circuit.)

The two-tone test: checking a transmitter's cleanliness

To check whether an SSB transmitter is producing a clean signal, hams use a two-tone test. You feed in two audio tones and look at the output on a scope.

• The signals used are two non-harmonically related audio signals. ("Non-harmonically related" means the two tones are not simple multiples of each other, like 700 Hz and 1900 Hz, so they do not hide each other's distortion.)
• The performance parameter it analyzes is linearity, that is, whether the transmitter amplifies faithfully without adding distortion. A non-linear transmitter splatters onto neighboring frequencies; the two-tone test reveals it.

The directional wattmeter

A directional wattmeter sits in your feed line and measures power flowing in both directions, the forward power heading out to the antenna and the reflected power bouncing back. From those two numbers it can show you standing wave ratio (SWR), a measure of how well your antenna and feed line are matched. (Lots of reflected power means a poor match and a high SWR.)

The antenna analyzer

An antenna analyzer is a small battery-powered instrument that generates its own tiny test signal so it can measure your antenna system directly, without needing your transmitter.

• To measure SWR with it, you must connect it to the antenna and feed line. (It needs the whole system attached to see the real match.)
• It can also measure the impedance of coaxial cable. (Impedance is a measure of opposition to AC signals, measured in ohms; coax is commonly 50 ohms.) So it does more than SWR.
• Watch out for strong signals from nearby transmitters, that received power can interfere with SWR readings, because the analyzer's own tiny signal gets swamped. If your readings look crazy, suspect a strong nearby station and try again later.

This group has two intertwined themes. First, RFI (radio-frequency interference), keeping your transmitter's energy out of audio gear, and figuring out what is causing a buzz. Second, grounding and bonding, the wiring that keeps you safe and your station quiet. They overlap because good grounding prevents a lot of interference.

Identifying interference by its sound

You can often guess what is interfering just by how it sounds in an audio device (a stereo, telephone, or speaker):

• RFI from a single-sideband (SSB) phone transmitter sounds like distorted speech, you hear garbled, unintelligible voice.
• RFI from a CW (Morse) transmitter sounds like on-and-off humming or clicking, matching the rhythm of the dots and dashes.

Tracking down and curing RFI

• Interference covering a wide range of frequencies (it is everywhere, not just one spot) is often caused by arcing at a poor electrical connection. A loose, corroded connection sparks, and a spark is a tiny broadband transmitter. Tighten or repair it.
• To reduce RFI getting into audio-frequency circuits, a bypass capacitor can help. (It gives the unwanted high-frequency RF a short, easy path to ground, shunting it away before it reaches the audio.)
• To reduce RFI caused by common-mode current on an audio cable, place a ferrite choke on the cable. ("Common-mode current" is unwanted RF riding along the outside of a cable; a ferrite choke, a clip-on ring of magnetic material, blocks it while letting the real signal pass.)

Grounding done right: bonding

The single most important word here is bonding, connecting all your equipment cases together with short, heavy conductors so they sit at the same electrical potential. Several questions all point back to this idea:

• To minimize the effects of ground loops, bond equipment enclosures together. (A ground loop is when two pieces of gear reach ground by different-length paths, creating a loop that picks up hum. Bonding the cases together removes the difference.)
• To minimize RF "hot spots" in a station (spots where you might get an RF burn), the technique is again bonding all equipment enclosures together.
• A symptom of a ground loop in your audio connections is that you receive reports of "hum" on your transmitted signal. If people say you sound like you have a buzz, suspect a ground loop.

When grounding goes wrong: RF burns and resonant grounds

• A possible cause of high voltages that produce RF burns is that the ground wire has high impedance on that frequency. (A ground wire that is a poor path for RF lets voltage build up at the equipment, and touching the case can sting you.)
• A possible effect of a resonant ground connection (where the ground wire happens to be a length that resonates at your operating frequency) is high RF voltages on the enclosures of station equipment. Same problem, different cause: keep ground leads short so they are not resonant.

Safety grounding and lightning

• Why must all metal enclosures of station equipment be grounded? It ensures that hazardous voltages cannot appear on the chassis. ("Chassis" means the metal frame or case.) If a fault inside a piece of gear puts dangerous voltage on the case, a good ground carries it safely away instead of into you. This is purely a safety rule.
• Why should you not use soldered joints in lightning-protection ground connections? Because a soldered joint will likely be destroyed by the heat of a lightning strike. Lightning carries enormous current; it melts solder instantly. Use bolted or clamped mechanical connections for lightning grounds.

This group mixes two ideas: a transmit control called the speech processor, and the S meter with the decibel math behind signal strength. There is a little arithmetic here, but it is all built on one friendly unit, so let's start there.

The speech processor

A speech processor is a transmit control that squeezes the loud and soft parts of your voice closer together. Its purpose is to increase the apparent loudness of transmitted voice signals, you sound "punchier" and easier to copy in a pileup or weak conditions. Two more facts:

• It works by increasing the average power of an SSB signal. (SSB power normally jumps around with your voice; the processor keeps it high more of the time, so the average goes up without raising the peak.)
• If you set it incorrectly, the result is "all these choices are correct": distorted speech, excessive background noise, AND excess intermodulation products. (Intermodulation products are unwanted extra signals that splatter onto nearby frequencies.) So use a speech processor with restraint, a little helps, too much makes you sound terrible and interferes with others.

The S meter and the decibel

The S meter on your receiver measures received signal strength, how strong the incoming signal is, on a scale of S1 (very weak) up to S9, and beyond S9 in decibels. To understand the scale you need the decibel (dB), which is simply a compact way to express how many times stronger one signal is than another.

Here is the only decibel fact you must hold onto for this group:

• Every 10 dB means 10 times the power. So 20 dB means 10 × 10 = 100 times the power, and 30 dB would mean 1000 times. Each "10 dB" multiplies by another 10.

Now apply it to the S meter:

• One S unit represents about 6 dB of change in signal strength. (So jumping from S7 to S8 is roughly a 6 dB increase.)
• A signal reading "20 dB over S9" is 100 times more powerful than one reading S9. (Because 20 dB = 10 × 10 = 100 times, exactly as above.)
• To raise a distant receiver's reading from S8 to S9 (one S unit, about 6 dB), you must raise your transmitter power by approximately 4 times. (Doubling power is 3 dB, so two doublings, 4× total, gives about 6 dB, one full S unit.)

Memory trick: one S unit = 6 dB = about 4 times the power. And every extra 10 dB over S9 means another ×10.

Keeping a sideband signal inside the band

An SSB voice signal is about 3 kHz wide, and that width sits on one side of your displayed carrier frequency. Which side depends on the mode:

• LSB (lower sideband) puts your signal below the displayed frequency. So a 3 kHz LSB signal with the dial set to 7.178 MHz actually occupies 7.175 MHz to 7.178 MHz (it spreads downward by 3 kHz).
• USB (upper sideband) puts your signal above the displayed frequency. So a 3 kHz USB signal with the dial set to 14.347 MHz occupies 14.347 MHz to 14.350 MHz (it spreads upward by 3 kHz).

Because your signal spreads out from the dial reading, you must keep the dial back from the band or segment edge so the whole signal stays legal:

• Near the lower edge of a phone segment using LSB, your displayed carrier should be at least 3 kHz above the edge of the segment (since LSB spreads downward, you leave 3 kHz of room below).
• Near the upper edge of a band using USB, your displayed carrier should be at least 3 kHz below the edge of the band (since USB spreads upward, you leave 3 kHz of room above).

Memory trick: the dial is at one end of your signal, and the signal stretches 3 kHz toward the band edge, so always leave a 3 kHz cushion on whichever side your sideband spreads.

This final group is about operating away from the comfortable home shack, in a vehicle (mobile) or off batteries and solar panels (portable). The themes are short antennas, clean power, and safe battery charging.

Short antennas on a moving vehicle

A full-size HF antenna can be tens of feet long, far too big for a car. So mobile antennas are physically short and use tricks to work anyway. Two parts you should know:

• A capacitance hat (a small disc or spokes near the top of a whip antenna) serves to electrically lengthen a physically short antenna. It fools the antenna into behaving like a longer one without actually being longer.
• A corona ball (a smooth metal ball on the very tip) is there to reduce RF voltage discharge from the tip of the antenna while transmitting. ("Corona" is the faint glow and hiss of electricity leaking off a sharp point; the smooth ball stops that loss.)

Short antennas come with downsides. The main one to remember:

• A disadvantage of a shortened mobile antenna versus a full-size one is that the operating bandwidth may be very limited. ("Bandwidth" here means how wide a range of frequencies it works over before you must re-tune; a short antenna covers only a narrow sliver.)
• The thing that most limits an HF mobile installation is the efficiency of the electrically short antenna. The short antenna, not the radio, is the weak link, much of your power is lost rather than radiated.

Powering a mobile radio

A 100-watt HF transceiver draws a lot of current, around 20 amps on transmit, so it needs a heavy, direct power feed.

• The best fused power connection for a 100-watt HF mobile install runs to the battery using heavy-gauge wire. (Going straight to the battery with thick wire gives the cleanest, strongest power.)
• You should not power a 100-watt radio from the vehicle's auxiliary power socket (the cigarette-lighter-style socket) because the socket's wiring may be inadequate for the current drawn by the transceiver. That thin wiring and small fuse cannot handle 20 amps.

Interference in a vehicle

What in a modern car can cause receive interference to an HF radio? The answer is "all these choices are correct": the battery charging system (the alternator), the fuel delivery system (electric fuel pumps and injectors), AND the control computers. A modern vehicle is full of electronics that all generate noise, so any of them can be the culprit.

Solar power and battery charging

For portable and off-grid operating, hams often charge a battery from a solar panel (also called a photovoltaic, or PV, panel). A panel is built from many small cells wired together.

• The individual cells in a solar panel are connected in a series-parallel configuration. (Putting cells in series adds up their voltages; putting strings in parallel adds up their current. Series-parallel gives both the voltage and the current you need.)
• A fully illuminated silicon photovoltaic cell produces an open-circuit voltage of about 0.5 VDC. (That is why many cells must be stacked in series to reach a useful voltage.)

Charging a battery safely needs two protective parts:

• A series diode between the panel and the battery is there to prevent discharge of the battery through the panel during times of low or no illumination. (A diode is a one-way valve for current. At night, without it, your battery would quietly drain backward into the dark panel; the diode blocks that reverse flow.)
• When charging a lithium iron phosphate (LiFePO4) battery, the precaution is that the solar panel must have a charge controller. (A charge controller regulates the voltage and current going into the battery; lithium chemistries especially need this to avoid overcharging and damage.)