G-4
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SUBELEMENT G4 – AMATEUR RADIO PRACTICES
[5 Exam Questions – 5 groups]
G4A – Station Operation and set up
The transceiver is set to different transmit and receive frequencies when operating a transceiver in “split” mode. To reduce interference from carriers in the receiver passband is the purpose of the “notch filter” found on many HF transceivers. To avoid interference from stations very close to the receive frequency is a use for the IF shift control on a receiver. Common use for the dual VFO feature on a transceiver to permit monitoring of two different frequencies. Use the attenuator function on HF transceivers is to reduce signal overload due to strong incoming signals
To reduce distortion due to excessive drive use Automatic Level Control (ALC) with an RF power amplifier. A pronounced dip reading on the plate current meter of a vacuum tube RF power amplifier indicates correct adjustment of the plate tuning control. Maximum power output without exceeding maximum allowable plate current is the correct adjustment for the load or coupling control of a vacuum tube RF power amplifier.
Excessive drive power can lead to permanent damage to a solid-state RF power amplifier.
Advantage of selecting the opposite or “reverse” sideband when receiving CW signals on a typical HF transceiver is it may be possible to reduce or eliminate interference from other signals. A time delay sometimes included in a transmitter keying circuit to allow time for transmit-receive changeover operations to complete properly before RF output is allowed. Automatic generation of strings of dots and dashes for CW operation is the purpose of an electronic keyer.
SWR Bridge is often used to match transmitter output impedance to an impedance not equal to 50 ohms.
Improper action of ALC distorts the signal and can cause spurious emissions when transmitting AFSK signals with the radio using single sideband mode.
VOX circuit does not un-key the transmitter, transmitter signal is distorted and frequent connection timeouts are a symptom of transmitted RF being picked up by an audio cable carrying AFSK data signals between a computer and a transceiver.
G4B – Test and monitoring equipment; two-tone test
Oscilloscope is a piece of test equipment that contains horizontal and vertical channel amplifiers. An advantage of an oscilloscope versus a digital voltmeter is that complex waveforms can be measured. An oscilloscope is the best instrument to use when checking the keying waveform of a CW transmitter. The attenuated RF output of the transmitter is connected to the vertical input of an oscilloscope when checking the RF envelope pattern of a transmitted signal. Two non-harmonically related audio signals are used to conduct a two-tone test. Linearity transmitter performance is analyzed by a two-tone test.
High input impedance is desirable for a voltmeter because it decreases the loading of circuits being measured. Better precision for most uses is an advantage of a digital voltmeter as compared to an analog voltmeter. When adjusting tuned circuits is an instance in which the use of an instrument with analog readout may be preferred over an instrument with a digital readout.
A field strength meter may be used to monitor relative RF output when making antenna and transmitter adjustments. The radiation pattern of an antenna can be determined with a field strength meter. Standing wave ratio can be determined with a directional wattmeter.
Antenna and feed line must be connected to an antenna analyzer when it is being used for SWR measurements. Strong signals from nearby transmitters can affect the accuracy of measurements when making measurements on an antenna system with an antenna analyzer. Determining the impedance of an unknown or unmarked coaxial cable is a use for an antenna analyzer other than measuring the SWR of an antenna system.
G4C – Interference with consumer electronics; grounding; DSP
Bypass capacitor might be useful in reducing RF interference to audio frequency devices. Distorted speech is heard from an audio device or telephone if there is interference from a nearby single sideband phone transmitter. On-and-off humming or clicking is the effect on an audio device or telephone system if there is interference from a nearby CW transmitter. Placing a ferrite choke around the cable would reduce RF interference caused by common-mode current on an audio cable. Arcing of a poor electrical connection could be a cause of interference covering a wide range of frequencies.
High RF voltages on the enclosures of station equipment can be caused by a resonant ground connection. The ground wire has high impedance on that frequency if you receive an RF burn when touching your equipment while transmitting on an HF band, assuming the equipment is connected to a ground rod. Connect all equipment grounds together is one good way to avoid unwanted effects of stray RF energy in an amateur station. Ground loop can be avoided by connecting all ground conductors to a single point. You receive reports of “hum” on your station’s transmitted signal is a symptom of a ground loop somewhere in your station.
A Digital Signal Processor (DSP) filter can perform automatic notching of interfering carriers. A function of a digital signal processor to remove noise from received signals. A wide range of filter bandwidths and shapes can be created is an advantage of a receiver DSP IF filter as compared to an analog filter
G4D – Speech processors; S meters; sideband operation near band edges
Increase the intelligibility of transmitted phone signals during poor conditions is the purpose of a speech processor as used in a modern transceiver. A speech processor affects a transmitted single sideband phone signal by increasing average power. Distorted speech, splatter and excessive background pickup are the result of an incorrectly adjusted speech processor. An S meter is found in a receiver. An S meter measures received signal strength.
A signal that reads 20 dB over S9 compare to one that reads S9 on a receiver is 100 times more powerful, assuming a properly calibrated S meter. Power output of a transmitter must be raised approximately 4 times to change the S meter reading on a distant receiver from S8 to S9.
At least 3 kHz above the edge of the lower edge of the 40-meter General Class phone segment when your displayed carrier frequency is using 3 kHz wide LSB. At least 3 kHz below the edge of the band when using the 20-meter General Class band and when your displayed carrier frequency is using 3 kHz wide USB. 7.175 to 7.178 MHz frequency range is occupied by a 3 kHz LSB signal when the displayed carrier frequency is set to 7.178 MHz. 14.347 to 14.350 MHz frequency range is occupied by a 3 kHz USB signal with the displayed carrier frequency set to 14.347 MHz.
G4E – HF mobile radio installations; emergency and battery powered operation
To electrically lengthen a physically short antenna is the purpose of a capacitance hat on a mobile antenna. To reduce high voltage discharge from the tip of the antenna is the purpose of a corona ball on a HF mobile antenna. Operating bandwidth may be very limited is one disadvantage of using a shortened mobile antenna as opposed to a full size antenna. The antenna system is what most limits the effectiveness of an HF mobile transceiver operating in the 75-meter band.
Direct to the battery using heavy gauge wire with a fused power connections would be the best for a 100 watt HF mobile installation. It is best NOT to draw the DC power for a 100 watt HF transceiver from a vehicle’s auxiliary power socket because wiring may be inadequate for the current drawn by the transceiver. The battery charging system, fuel delivery system and vehicle control computer may cause interference to be heard in the receiver of an HF radio installed in a recent model vehicle
Photovoltaic conversion is the name of the process by which sunlight is changed directly into electricity. 0.5 VDC is the approximate open-circuit voltage from a fully illuminated silicon photovoltaic cell. A series diode is connected between a solar panel and a storage battery that is being charged by the panel to prevent self-discharge of the battery though the panel during times of low or no illumination. A large energy storage system is needed to supply power when the wind is not blowing is a disadvantage of using wind as the primary source of power for an emergency station.
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