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This covers some aspects of the correct set-up of station equipment, and equipment used to aid this set-up.
As mentioned in my Technician notes, combinations of capacitors, inductors, resistors, and sometimes operational amplifiers can be combined to form filters. In some cases these can be tuned for frequency, slope or notch-width, and amount of cut or boost. Notch filters are mentioned in the questions, and these can be used to remove things like annoying carriers, digital signals, and the like, although if there are digital signals it may be worth checking whether you really should be operating voice there!
DSP stands for Digital Signal Processing, and often uses a fairly powerful specialised processor.
It is possible to purchase external devices which connect between the radio's audio output and the speaker or headphones. BHi is one example, and Timewave devices are available used. BHi also make a speaker with inbuilt DSP.
Many modern radios contain DSP ICs, which on intermediate grade radios is applied to the audio frequencies, and in more expensive radios, in the IF (intermediate frequency) stage, and in many, the conversion to audio is also done by DSP. Radios which do this are sold as "Software Defined Radios".
DSP can work as simple filters, cutting out low and high audio frequencies, automatically "notch out" carriers and other tones (including Morse); and also reduce noise in the audio passband. The amount of DSP can be adjusted, as at its most aggressive, it can make the voice sound metallic or robotic. It can also kill music. Some DSP may have mode settings, so it does not kill Morse.
DSP is not all-powerful, so a good quality filter, such as the Collins / Inrad mechanical filter provides the DSP with the best possible signal to work with.
At one point I played with some PC software (free download) which performed waterfall and DSP filtering.
A range of devices, from the low cost "Soft-rock" and similar devices, which down-convert a section of the band down to a band of audio frequencies, which can then be processed by a PC, using its sound-card as the input; to very expensive radios, either as a box controlled by a PC, or with traditional front panels. It is also possible to simply amplify the RF signal and feed it into a card for recording composite video. Small USB connected (European / Australian) DVB-T TV receiver dongles can be used to receive VHF and UHF radio signals, with suitable software.
In days of old, the typical HF Ham transmitter or transceiver included at least a valve final stage. Now 100 watts PEP output can be achieved from 160 to 6 metres (or even 4 metres) using one device. However, valves or tubes remain popular for HF linear amplifiers, and can be quite affordable, especially if using Soviet, Russian, or Chinese devices. It is also possible to generate around 600 watts using Motorola transistors mounted on a copper heat spreader, then a heatsink. While voltages are less likely to be dangerous, it is easy enough to stuff-up, and destroy these devices.
The questions relating to the operation of tube amplifiers also relates to setting up tube final transceivers, and to tube based ex-broadcast transmitters, although the latter tend to only need periodic adjustment.
An example of a rig with a tube final is the Kenwood TS-820S, dating from 1979, which features both a mechanical dial, and a digital frequency display. This has a Drive control for the drive valve circuit, and Load and Plate controls for the final valve amplifier circuit. If you wish to see the manual, it is on the Kenwood site: TS-820S Manual (PDF).
The FT-101 series from Yaesu was a competing product line.
There are a range of devices used to test the SWR and for finding the resonant frequency of an antenna.
The SWR Meter has either a single meter movement and a switch for forward or backwards, or a crossed needle meter with two movements on one dial, allowing more direct reading. Some modern transceivers have a built in SWR metering function.
Directional RF watt-meters, especially the Bird 43, with changeable metre "slugs" or elements, each for a specific power level and frequency range are probably the most accurate.
Both of these devices above use energy from a transmitter to make the readings. Something like finding the resonant frequency of a helically wound mobile antenna for 80 metres requires multiple readings at many frequencies across, and sometimes beyond, the band.
Working without a transmitter, using an internal oscillator, the Antenna Analyser can perform a range of tests on an antenna to reveal its complex impedance, including whether it is inductive or capacitive (such as 42+27J Ω), and can show resonant frequency. The exam indicates that they can be used to determine the characteristic impedance of coaxial cable. Some will show a frequency vs SWR plot on an LCD screen.
Most recently, the NanoVNA product has become available, at prices below most analysers, and likely more useful. These are based on the very expensive Vector Network Analyser.
A bit off topic, a spectrum analyser and tracking oscillator can be used to analyse antenna system components such as filters, including the cavity filters used it repeaters. VNAs and NanoVNAs also perform this task.
These are usually quite simple circuits, containing just a short antenna (around 10 cm), a germanium or point-contact diode, a ceramic capacitor, and a meter movement, and perhaps a potentiometer to vary the sensitivity. This is very similar to a microwave oven leakage detector. A few include an op-amp.
Most just have a simple 0 to 10 scale, allowing only for relative signal readings. They can be used to compare field strength, for things like evaluating the pattern of antennas, or the relative forward gain of two devices. Devices which give absolute readings are much more complex, and require careful calibration.
Many SWR meters include a basic FS meter.
They certainly cannot assess the quality of a signal, such as distortion of any kind.
A multimeter combined several functions, most often volts and ohms, plus milliamps and/or amps, sometimes given the name V-O-M meter. Simpson Electric sell their $500+ "Made in USA" analogue meters as "VOM multimeters".
There are two primary types, digital and analogue. Digital meters use LCD, OLED, LED, or fluorescent digits. These give a good resolution, with displays going up to 1999, 2999, 3199, 3999, 5999, or 19999, as examples. As 0 is one of the values which can be displayed, meters are sold as 2000 count, 6000 count, etc.
Analogue meters use the sweep of a needle across a calibrated scale to indicate values. For voltage and current tests, most meters are operated only by the energy of the circuit under test. Up-market analogue meters include a valve amplifier (a VTVM, Vacuum Tune Volt Meter) or a FET (field effect transistor) amplifier. These increase the input impedance of the meter.
High input impedance means that the meter puts a lower load on the circuit under test. In many cases this is unimportant, but if the circuit has high impedance, then this avoids excessive loading on the circuit, which drags the voltage down, giving a false reading.
If one were to form a voltage divider from a 560 kΩ resistor, and a 910 kΩ resistor we would have 61.9%* of the supply voltage at the junction, which we can place on one input of a comparator (LP311). Were we to measure this with a 10 mega-ohm input digital meter, or a VTVM (vacuum-tube voltmeter) the loading will be small. That said there would still be an error. However, a 20 kΩ per volt analogue meter on the 5 volt range would place a load of 100k on this circuit, totally swamping it, and giving a reading of a fraction of what it should be. There are some digital meters with significantly higher input impedance, such as Keithley's "Electrometer" products.
I listed some useful meters on my Technician Operations page, along with further comments, and photos.
* The 61.9% figure above was selected, as using this as the reference ratio for a comparator IC allows a simple timer to be made using a simple Resistor-Capacitor combination, with the period being one time constant, or R × C.
While analogue meters only read positive DC voltages or currents, digital meters simply display the value with a minus sign (-). A few metres even change mode automatically on voltage readings, displaying AC or DC based on which is the prominent value, although this can be over-ridden.
Some meters incorporate a clamp which can measure current without cutting the wire. There are also external current measuring clamps available. Many use a current transformer. In a CT the lead carrying current is the single turn primary of a transformer, outputting a smaller current. It appears that external clamp meters include a shunt resistor, which converts the current to a voltage, so the output is 1 millivolt per amp; and to prevent hazardous voltages appearing on the terminals. Some use a hall effect device instead. The most important thing to note is that the current carrying conductors mist be separated, otherwise there will be no differential current flow through the transformer, so no output.
A CT or other sensitive clamp tester can be used with both power wires, or with power and earth wires all going through the clamp, to detect leakage currents to earth, either going back through the ground wire, or through an alternative earth path (telecom or radio earth, for example). Looking for an imbalance in the power wires is how GFCI / RCD / ELCBR safety switches work.
Some large 3-phase pole transformers in rural NSW include a CT on each phase, feeding three analogue meters, large enough to be visible from the ground. Presumably these assist in balancing loads across the phases, when a new customer is added, etc.
The original 'scopes was the "Cathode Ray Oscilloscope", consisting of a CRT with a grid in front of the phosphor face. Typically, even in non-metric countries, this is in centimetres, with a central lines marked with 2mm increments. The vertical know selects the number of millivolts or volts per centimetre, or per division, 10 cm being the typical total height. If the signal is a sinewave, then trace is set to the centre of the scale, such that positive and negative excursions can be displayed. The horizontal knob is for micro-, milli-, or whole seconds per division. Again, 10 to 12 cm is typical.
The main input is also called the X-input, as a voltage on it deflects the beam up or down, the X-axis.
The typical CRO has 1 MΩ input impedance. A 10x probe can be used which divides the reading by 10, but increases the input impedance by 10 as well.
Before digital meters, CROs were sometimes used as meters on high-Z circuits.
The horizontal knob has a position which allows the Y-input, which deflects the beam left or right. If signals of the same frequency are presented to the X and Y inputs, a circle will be displayed. If one is double, then the signal will be an 8 or an infinity symbol, ∞. If one is three times, you get the ABC (Australia) logo! Yes, this lisojenious curve was the origin of the logo.
TV and older computer monitor screens use magnetic fields to deflect the beams. CROs use electrostatic deflection, which can operate at higher frequencies. The CRO thus includes both horizontal and vertical amplifiers to drive the deflection plates.
Some CROs have two or more (vertical) channels. These can display things like a TV field one one line, and just a single, selected line on the other. There are also fancy analogue storage units, which are very complex devices.
There are also digital storage oscilloscopes (DSOs) which in many cases use LCD displays.
If a modulated signal is put into the X or vertical input, with the normal timebase running, then an envelope will be displayed. For an audio sinewave feeding an AM transmitter this will be a sinewave in the upper of the display, and a mirrored one at the bottom, the space between filled with a dim trace. A well modulated signal will have maybe a 90% reduction in level, and a 90% increase. With good processing a signal may have 95% downward modulation, and 125% upward modulation, this called asymmetrical modulation; although this is normally done in broadcasting, rather than ham radio. That said, the 160 metre broadcast from ARNSW uses asymmetrical AM, as they have a broadcast transmitter.
For a Morse signal the envelope should not be a square-wave, but should have a rounding at the top, and also as it drops away. This avoids key-clicks being heard outside the signal's normal bandwidth.
Even an old Tekronix or Australian made BWD CRO is most useful for understanding the behaviour of many circuits.
These are actual questions from the General exam pool.
What is the purpose of the "notch filter" found on many HF transceivers?
A. To restrict the transmitter voice bandwidth
B. To reduce interference from carriers in the receiver passband
C. To eliminate receiver interference from impulse noise sources
D. To enhance the reception of a specific frequency on a crowded band
If a carrier or other signal is in the receiver passband, it will be heard as a tone, whine, or whistle. A notch filter removes or reduces this tone, answer B.
These can be manually set analogue device, or part of a DSP (digital signal processing) function, internal or external to the radio, in which case the notching may be done automatically.
What is one advantage of selecting the opposite or "reverse" sideband when receiving CW signals on a typical HF transceiver?
A. Interference from impulse noise will be eliminated
B. More stations can be accommodated within a given signal passband
C. It may be possible to reduce or eliminate interference from other signals
D. Accidental out of band operation can be prevented
Radios such as the '857D have a range of modes such as AM, FM, DIG, USB, LSB, CW, and CW-R. Selecting CW-R helps reduce interference which would otherwise be heard using CW, answer C.
What is normally meant by operating a transceiver in "split" mode?
A. The radio is operating at half power
B. The transceiver is operating from an external power source
C. The transceiver is set to different transmit and receive frequencies
D. The transmitter is emitting an SSB signal, as opposed to DSB operation
When working pile-ups for a rare DX station, you must transmit away from his or her frequency, usually around 5 or so kHz up, but this varies. It is using different frequencies that is called "split" operation, answer C.
Many radios allow you to select between VFO A or VFO B, or SPLIT. Larger radios may have separate dials for this, in smaller radios a regular or "soft" button (on the FT-857D these are the buttons below the display which have multiple functions, depending on the selection using knob on the lower left) select which one the dial is tuning.
The A and B VFOs can be handy for switching between 2 metres SSB around 144.150 MHZ, and 2 metres FM around 146.500 or 146.520 MHz. Set this up for 6 m and 70 cm too. This is useful during some VHF contest where there are both SSB and FM stations.
What reading on the plate current meter of a vacuum tube RF power amplifier indicates correct adjustment of the plate tuning control?
A. A pronounced peak
B. A pronounced dip
C. No change will be observed
D. A slow, rhythmic oscillation
A dip in the current, answer B, means correct tuning of this control, and the best efficiency, answer B.
What is a reason to use Automatic Level Control (ALC) with an RF power amplifier?
A. To balance the transmitter audio frequency response
B. To reduce harmonic radiation
C. To reduce distortion due to excessive drive
D. To increase overall efficiency
The ALC us used to prevent excessive drive into the amplifier causing distortion, answer C.
What type of device is often used to match transmitter output impedance to an impedance not equal to 50 ohms?
A. Balanced modulator
B. SWR Bridge
C. Antenna coupler or antenna tuner
D. Q Multiplier
An antenna coupler, or an antenna tuner, answer C, can match a transmitter to an antenna either which is being used on a frequency at which it is not resonant, or where it is resonant, but has a different impedance, such as a delta loop.
What condition can lead to permanent damage to a solid-state RF power amplifier?
A. Insufficient drive power
B. Low input SWR
C. Shorting the input signal to ground
D. Excessive drive power
Errors in using a solid-state RF power amplifiers can damage the output devices (LD-MOS or other transistors), requiring often expensive replacements, and excessive drive power is an example of this, answer D.
What is the correct adjustment for the load or coupling control of a vacuum tube RF power amplifier?
A. Minimum SWR on the antenna
B. Minimum plate current without exceeding maximum allowable grid current
C. Highest plate voltage while minimizing grid current
D. Maximum power output without exceeding maximum allowable plate current
This knob should be adjusted for maximum power without excessive plate current, answer D.
Why is a time delay sometimes included in a transmitter keying circuit?
A. To prevent stations from interfering with one another
B. To allow the transmitter power regulators to charge properly
C. To allow time for transmit-receive changeover operations to complete properly before RF output is allowed
D. To allow time for a warning signal to be sent to other stations
In stations which include things like transverters, pre-amplifiers, and/or power amplifiers, it is necessary to ensure the various devices are powered up, and ready for the signal, answer C, or switched out of the signal path, as required.
What is the purpose of an electronic keyer?
A. Automatic transmit/receive switching
B. Automatic generation of strings of dots and dashes for CW operation
C. VOX operation
D. Computer interface for PSK and RTTY operation
These are an electronic circuit which generate Morse dits and dahs using simple switch contacts as the input, rather than a complex mechanical device with a pendulum, answer B.
Which of the following is a use for the IF shift control on a receiver?
A. To avoid interference from stations very close to the receive frequency
B. To change frequency rapidly
C. To permit listening on a different frequency from that on which you are transmitting
D. To tune in stations that are slightly off frequency without changing your transmit frequency
These alter the receiver characteristics to help avoid interference from signals very close to the desired frequency, answer A.
Which of the following is a common use for the dual VFO feature on a transceiver?
A. To allow transmitting on two frequencies at once
B. To permit full duplex operation, that is transmitting and receiving at the same time
C. To permit monitoring of two different frequencies
D. To facilitate computer interface
Transceivers which include two VFOs can monitor two frequencies at once, answer C.
What is one reason to use the attenuator function that is present on many HF transceivers?
A. To reduce signal overload due to strong incoming signals
B. To reduce the transmitter power when driving a linear amplifier
C. To reduce power consumption when operating from batteries
D. To slow down received CW signals for better copy
The attenuator can reduce the level of strong, typically local, signals to prevent overload of the receiver, answer A.
What is likely to happen if a transceiver’s ALC system is not set properly when transmitting AFSK signals with the radio using single sideband mode?
A. ALC will invert the modulation of the AFSK mode
B. Improper action of ALC distorts the signal and can cause spurious emissions
C. When using digital modes, too much ALC activity can cause the transmitter to overheat
D. All of these choices are correct
AFSK signals (data and RTTY) result in the transmitter operating at full power while the signal is being transmitted, and if the automatic level control is set wrongly, this can result in a distorted signal, and the emission of spurious emissions, which can cause interference to other stations, answer B.
Which of the following can be a symptom of transmitted RF being picked up by an audio cable carrying AFSK data signals between a computer and a transceiver?
A. The VOX circuit does not un-key the transmitter
B. The transmitter signal is distorted
C. Frequent connection timeouts
D. All of these choices are correct
RF getting back into the audio leads can lock-up the transmission which uses VOX, it results in the transmission of distorted signals, and it can make the connection drop-out, so all, answer D.
How does a noise blanker work?
A. By temporarily increasing received bandwidth
B. By redirecting noise pulses into a filter capacitor
C. By reducing receiver gain during a noise pulse
D. By clipping noise peaks
Noise blankers reduce the impact of impulse noise by reducing gain during these pulses, answer C.
What happens as the noise reduction control level in a receiver is increased?
A. Received signals may become distorted
B. Received frequency may become unstable
C. CW signals may become severely attenuated
D. Received frequency may shift several kHz
Cranking up the DSP can cause the voice to become metallic and distorted, answer A.
What item of test equipment contains horizontal and vertical channel amplifiers?
A. An ohmmeter
B. A signal generator
C. An ammeter
D. An oscilloscope
This is the oscilloscope, which displays signals on a screen, answer D.
While for many uses, the internal ramp generator provides the horizontal component, there are tasks, such as frequency comparison, where both X and Y inputs are used.
Which of the following is an advantage of an oscilloscope versus a digital voltmeter?
A. An oscilloscope uses less power
B. Complex impedances can be easily measured
C. Input impedance is much lower
D. Complex waveforms can be measured
A 'scope allows measurement and visualisation of complex waveforms, and determination of peak or peak-to-peak voltages on these, answer D.
Budget digital meters do not give accurate RMS readings for waveforms other than sine-waves, and thus peak values cannot be accurately calculated. Also, thingsd like clipping and gross distortion can be observed, and likewise the duration of pulses.
Which of the following is the best instrument to use when checking the keying waveform of a CW transmitter?
A. An oscilloscope
B. A field strength meter
C. A sidetone monitor
D. A wavemeter
Again, this is the CRO, or oscilloscope, answer A.
A variation on this is the "station monitor" or similar product, usually available as an accessory for the flagship valve based home station rigs.
What signal source is connected to the vertical input of an oscilloscope when checking the RF envelope pattern of a transmitted signal?
A. The local oscillator of the transmitter
B. An external RF oscillator
C. The transmitter balanced mixer output
D. The attenuated RF output of the transmitter
An ATTENUATED sample of the RF output of the transmitter, answer D, is connected to the vertical input of the "silly-scope".
Why is high input impedance desirable for a voltmeter?
A. It improves the frequency response
B. It decreases battery consumption in the meter
C. It improves the resolution of the readings
D. It decreases the loading on circuits being measured
A high input impedance means that it places less load on the circuit being tested, answer D.
This is important to provide accurate readings in high impedance circuits, and even to not affect the operation of the circuit under test due to loading.
What is an advantage of a digital voltmeter as compared to an analog voltmeter?
A. Better for measuring computer circuits
B. Better for RF measurements
C. Better precision for most uses
D. Faster response
These generally have greater precision, answer C.
A digital meter can directly display a voltage, such as 13.47 volts, while on the 25 volt range of an analogue meter, you will only have marks for each half volt, and can really only guestimate to a quarter volt. An example is here: Tech Operations.
What signals are used to conduct a two-tone test?
A. Two audio signals of the same frequency shifted 90 degrees
B. Two non-harmonically related audio signals
C. Two swept frequency tones
D. Two audio frequency range square wave signals of equal amplitude
Two fixed signals which are not harmonically related are used for this test, answer B.
Which of the following instruments may be used to monitor relative RF output when making antenna and transmitter adjustments?
A. A field strength meter
B. An antenna noise bridge
C. A multimeter
D. A Q meter
A field strength meter displays allows you to compare field strength, usually only displaying a nominal value, answer A.
Which of the following can be determined with a field strength meter?
A. The radiation resistance of an antenna
B. The radiation pattern of an antenna
C. The presence and amount of phase distortion of a transmitter
D. The presence and amount of amplitude distortion of a transmitter
By taking multiple readings around an antenna, at some distance, the radiation pattern can be determined, answer B.
Which of the following can be determined with a directional wattmeter?
A. Standing wave ratio
B. Antenna front-to-back ratio
C. RF interference
D. Radio wave propagation
By taking forward and reflected power readings, and performing calculations, the SWR can be determined, answer A.
Which of the following must be connected to an antenna analyzer when it is being used for SWR measurements?
C. Antenna and feed line
D. All of these choices are correct
The antenna feedline and antenna are connected to the analyser, answer C.
There is no need for other equipment, as the analyser contains an RF oscillator.
What problem can occur when making measurements on an antenna system with an antenna analyzer?
A. Permanent damage to the analyzer may occur if it is operated into a high SWR
B. Strong signals from nearby transmitters can affect the accuracy of measurements
C. The analyzer can be damaged if measurements outside the ham bands are attempted
D. Connecting the analyzer to an antenna can cause it to absorb harmonics
You cannot damage the analyser by connecting it to an un-powered antenna on a stand-alone site, no matter how bad SWR, but high power signal coming back down the feedline from nearby transmitters, can, at the very least affect the measurements, answer B, and could damage the device if very high.
Also, be careful using these devices on multiplexed sites, say adding a 70 cm repeater into an antenna system with other UHF services. Is the last distractor referring to harmonics of a 2 metre signal affecting readings on 70 cm? Perhaps, but that is not caused by the analyser, and it would also covered in B.
What is a use for an antenna analyzer other than measuring the SWR of an antenna system?
A. Measuring the front to back ratio of an antenna
B. Measuring the turns ratio of a power transformer
C. Determining the impedance of an unknown or unmarked coaxial cable
D. Determining the gain of a directional antenna
These analysers can measure impedance, so this can be applied to determining if a cable is 50 ohm, 75 ohm, or something else, answer C. Certainly, dodgy coax, or deteriorated coax can vary in its impedance.
Good quality coax may be available as short ends off reels at hamfests.
What is an instance in which the use of an instrument with analog readout may be preferred over an instrument with digital readout?
A. When testing logic circuits
B. When high precision is desired
C. When measuring the frequency of an oscillator
D. When adjusting tuned circuits
When adjusting tuned circuits we are often looking for a maximum or minimum in the signal, not an exact level. This is often easier to spot when we are watching a needle, rather than looking for trends in a bunch of digits.
What type of transmitter performance does a two-tone test analyze?
B. Percentage of suppression of carrier and undesired sideband for SSB
C. Percentage of frequency modulation
D. Percentage of carrier phase shift
This allows the linearity of the transmitter to be analysed, answer A.
On to: Amateur Practices 2 - Interference, DSP, Speech processors, and S-meters
You can find links to lots more on the Learning Material page.
Written by Julian Sortland, VK2YJS & AG6LE, March 2022.
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