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Microphones convert audio into electrical signals. There are a few types, such as dynamic, which is a speaker working in reverse; the electret condenser microphone, which often include a tiny pre-amplifier, requiring a few volts at low current to power it.
It is important to note that while microphones may use the same connector, they may be wired differently, and PPT lines may vary between connecting to ground, or the line to a positive voltage. Some connectors include a voltage for powering amplifiers in the microphone, etc. Some with number pads include DTMF chips, others communicate with the radio's processor. Some radios also have a low level received audio output. Others have UP, DOWN, and FAST buttons, to allow tuning from the mike.
The desk-top radios for the Japanese makers use an 8 pin version of the screw-locked round microphone connector used in better CBs, but each uses a different wiring scheme. These have pins on the panel-mounted connector, and socket on the "plug". Mobile radios often use an 8 pin RJ-45 one, as used in PC networking.
Hand-helds use a range of connectors, one being the 3.5mm and 2.5mm pair, the larger for headphones or a speaker, the smaller for the microphone. These can be used for speaker-microphones, which can be clipped to an epaulette or jacket, or to a headset with a boom microphone. While there are moulded combination plugs, older Bakelite or hard plastic cased plugs will fit, allowing packet modems to be connected. Some use 4 contact 3.5 mm plugs, with a waterproofing screw-down cover, the Yaesu VX-7R* being an example. Adapters are also available to allow 2-pin microphones and modems / TNCs to be connected. The microphone connector has a voltage on it, both to power the electret microphone, and to sense when this is drawing current, when the microphone is put into circuit by the PTT switch. To key them with a TNC a resister to ground is switching into this line, while audio is fed via a capacitor, which provides DC isolation.
* Note that the similar looking Vertex-Standard VXA-700 Spirit comes with an adapter for aviation headsets, 6.5 mm (0.25") headphones, and 5.3mm (0.206 "). With standard settings these send the microphone audio to the headphones, so won't work with the handheld speaker-mikes use with the '7R.
For home or mobile radios, RF from the antenna system can sometimes get back into the microphone cable, causing distortion, or other radio misbehaviour. Clipping on a ferrite core may help.
Some radios have microphone gain controls, and if this is set too high for the connected microphone, the signal may become distorted. The same applies with sending packet, RTTY, or other digital modes.
I have used an old green Pye carbon microphone, as seen in "Party under Parliament House", with a HT, but have no idea how it sounded, other than that it worked. Carbon microphones are used in old telephones.
The power connection to the radio must be made using heavy copper cable. This must be fused. A topic of debate is the connection of the negative or return line. This should not be fused, or if it is, a value higher than the positive line. The point should be either the battery negative, or the body at or near the battery strap. The exam also says the engine grounding strap, which may not actually be ideal.
Regulated supplies maintain a near constant voltage output from low or zero current to the rated current, and thus prevent voltage fluctuations potentially affecting the electronics of the radio. The output of unregulated supplies can float to a high level when the radio is drawing little current due to being in receive mode and squelched. High mains voltages can translate to a higher than usual voltage on the secondary of the transformer, and thus on the output of an unregulated supply, or increase the heat disipated by a "linear" regulated supply.
The cable from the cable from the supply to the radio should be as short and as "chunky" possible. The lowest American Wire Gauge (AWG) or highest number of square millimetres has the lowest resistance. Replacement cables, and parts to make them, can be obtained from Powerwerx. Given fitting the heavier cables into "Powerpoles" is fiddly, pre-made ones may be easier.
Radios can be tuned in one or more ways.
Radios with SSB and/or CW often have a dial. On old radios this tuned a variable capacitor gang, or some other analogue tuning system. In modern radios it operates a "rotary encoder", which increments the frequency in small steps, such as 0.1 or 0.01 kHz, simulating a real dial.
FM radios may also have a dial, which steps through in steps set in the menu, such as 5, maybe 6.25, 10, 12.5, 15, 25, 30, and 50 kHz; and through memories in memory mode. A button may select larger steps, such as MHz.
Some radios also have a keypad, for "direct entry" of frequencies. The buttons may have multiple functions, so for some you press something like: Enter 14.220. On HTs they may assume frequency entry, so just type 147000 for 147 MHz. If you are transmitting the keypad becomes a DTMF keypad. Holding a numeral key, pressing F and a number, holding F for a moment, then a number may all initiate different settings, such as turning on or off CTCSS, or selecting the subtone; setting the step; or selecting +Repeater, -Repeater, or Simplex.
Outside the exam, older radios, especially HTs have thumb-wheels. An example for 2m might have three wheels. We must assume the first 14, for 140 MHz. The wheels then select MHz, hundreds of kHz, and 10s of kHz. A switch marked +5 adds the final 5kHz. Thus 665 means 146.650 MHz. 712+5 is 147.125 MHz, a WICEN channel. Duplex/Simplex and +/- switches, or +/0/- positions control repeater offset, fixed at 600 kHz. Some radios of this type will only transmit on the Ham bands, some require care not to transmit out of band. The Icom IC-2E and IC-2AT are examples, and these have been exactly copied.
Memories are a great way to store repeater channels, tones, and offsets; net frequencies; call channels; ARNSW / WIA news frequencies; and emergency communications group channels.
Many radios have some form of scanning function, where the radio steps through many channels per second, looking for a frequency where there is a signal. This is initiated either by holding an up or down button (including on a microphone), or pressing a "SCAN" button. Most radios allow both scanning in "VFO" mode, and through memories. It can be used to zip from one end of the band to the other, and tapping the PTT will stop scanning. The exam however tells you to use a memory for a favourite channel.
Beyond the exam, old PMR (commercial or government two-way radios) may have no frequency control, as the use a single receive / transmit crystal pair to operate on one channel, or one repeater; or they may have a dial to select from a small number of such crystal controlled channels or repeaters. Some may have a have a two digit LED display to select repeaters stored in a fixed EPROM or EEPROM memory, programmed on a PC and PROM programmer. More modern PMR radios can be programmed with a PC and cable. The Tait T500 series, such as the T535, are two channel radios which uses a matrix of diodes for programming, with these selected by bridging a pads with solder. While the multi-channel ones can be a cheap way to get on air, the low channel count ones are a good way of having a radio monitoring the local repeater, while using the main shack radio on other bands.
Some modes, such as AM and FM tolerate a moderate amount of frequency error in the transmit frequency, or in tuning of the receiver. In the case of SSB, with no carrier to reference the signal too, if there is a difference between the suppressed carrier frequency, and the tuning of the receiver, the audio will be unnaturally high, or unnaturally low. A knob, called the RIT, or Receiver Incremental Tuning, which tweaks the receiver. In some radios there is a switch for the RIT, allowing it to be stitched in, if one member of a group is off-frequency. 23 cm FM transceivers may also have a RIT, as getting to this frequency means many multiplication steps from the actual VFO frequency, and an error of a few 10s of Hertz can mean an error of several kilohertz, rather than a fraction of a kilohertz on a 2m radio. In SSB CB land this is called the Clarifier, a term used in the exam.
When a radio is tuned to a frequency on which there is no transmission, there speaker will emit noise or hash, which can be rather tiring. To silence the radio, most have a squelch feature. The sensitivity may be set by a knob or by a menu item. Squelch which does not use CTCSS, DCS or tone-burst is called "carrier squelch". It may be called "mute" on some radios. Noise can increase depending on the weather.
Automatic Gain Controlis used in most radios to limit the level of signals within the receiver. This includes keeping the audio level reasonably constant, despite variation in the received signal strength. Some radios have options to change the speed of AGC response to signal variation.
The Noise Blanker at least partially eliminates impulse interference, such as that caused by automotive ignition systems.
You will hopefully have noticed that we have discussed the bandwidth of different modes, such as CW, SSB, AM, and FM.
Depending on the mode, radios have different filters in the IF stage. Better multi-mode radios have several filters which can be switched in, depending on the mode.
For CW (Morse code) the signal's bandwidth is low, but not zero, as the keying on an off causes some bandwidth. The exam indicates the the IF bandwidth should be 500 Hz.
For SSB this is 2.2 to 3 kHz, with the exam listing 2.4 kHz. For AM around 6 kHz is used, and for FM, it is around 16 kHz, or 10.1 kHz in some cases.
It is possible to purchase extra filters (around US$140) to plug into radios, beside, or replacing existing filters. A prime example is the Collins Mechanical Filters, which were by Rockwell Collins, but they have ceased production, with remaining stock sold to Inrad, and running low. The standard filter in the FT-857D is a ceramic filter, listed as 2.2 kHz. This may not be as sharp as the 2.3 kHz Collins / Inrad one, which is considered an upgrade.
There is a Collins / Inrad 500 Hz one for CW, including for the 857D. Adding the CW filter is valuable, as while DSP can provide narrow filtering, of there are strong signals within the 2.2 kHz or whatever SSB channel width, the receiver's gain will be reduced by the AGC, and the weak signal of the station you are trying to hear will also be reduced. If the 500 Hz filter is fitted, and the strong local signal is outside this, the signal should be more easily received, and the DSP has the best possible signal to work with. If you are listening to a broadcast station, and the signal is good, a wide setting may sound more natural, especially if there is music.
Outside the exam, but when a strong signal near the frequency you are listening to reduces the sensitivity of the receiver, it is said to be "desensitised". This might happen when packet data is being sent from your checkpoint at fairly high power, while your are listening to weak voice stations on the same band.
PCs, running Windows or various Linux versions, can be used for a range of tasks. Those on the exam are: Logging contacts and contact information, sending and/or receiving CW, and generating and decoding digital signals. Logging can involve manually adding all data, or it can be read from the radio via a "CAT", meaning Computer Aided Transceiver interface; serial; or USB. These can also be used to control the radio; and for programming memories.
The radio and PC can be connected via the soundcard, which generates tones to go to the radio's microphone, and converts audio to digital form, where it can be further processed, or converted to text or images if a data or image mode is being received. An alternative is a USB soundcard; or via modems or TNCs. PCs can read the dits and dahs of Morse code; with accuracy depending partly on the sender's "fist", and These multiple uses trigger the "All of the above" option in the relevant question.
Removed from the exam in favour of more questions on using sound-card connections, the Terminal Node Controller is a device with includes a processor which assembles text into "packets", and a modem which converts these to audio tones, and keys the radio. It also demodulates the tones to packets, and so to text. Some contain message storage, and other smart functions. They connect to PCs (or Commodores, or MicroBees) via RS-323C; or to modern PCs via a USB adapter.
Likewise, from the days of DOS PCs, is the Baycom modem and software, where a small PCB contained a modem chip, but packet assembly and decoding was done in software.
SWR meters (and directional wattmeters) are placed in series with feedline, between transmitter and antenna.
Actual exam questions, from the published NCVEC Technician pool.
What must be considered to determine the minimum current capacity needed for a transceiver power supply?
A. Efficiency of the transmitter at full power output
B. Receiver and control circuit power
C. Power supply regulation and heat dissipation
D. All of these choices are correct
If a transmitter has a 100 watt output, but is only 50% efficient, then it needs 200 watts, which at 12 volts converts to 16.7 amps, add in an amp or so for the processor, any stand-by current used by the receiver and DSP, and additional losses and variations in current draw dur to variations in the supply output due to mains variation must also be taken into account, meaning all choices add up, answer D.
How might a computer be used as part of an amateur radio station?
A. For logging contacts and contact information
B. For sending and/or receiving CW
C. For generating and decoding digital signals
D. All of these choices are correct
PCs have all these uses, so answer D.
Why should wiring between the power source and radio be heavy-gauge wire and kept as short as possible?
A. To avoid voltage falling below that needed for proper operation
B. To provide a good counterpoise for the antenna
C. To avoid RF interference
D. All of these choices are correct
When the radio draws high current, such as an FT-857D running FM on 10 metres, the current draw in significant, and this causes an increased voltage drop, which could mean the supply drops below that needed for the radio to operate correctly, answer A. Thinking back to Ohm's law, heavy, short cable reduces these drops. Replacing the cable, either by making one yourself, or with a bought one, can be an option.
Which computer sound card port is connected to a transceiver’s headphone or speaker output for operating digital modes?
A. Headphone output
C. Microphone or line input
D. PCI or SDI
The audio output of the radio is connected to the input of the sound-card or on the laptop, marked line-in or microphone, answer C.
What is the proper location for an external SWR meter?
A. In series with the feed line, between the transmitter and antenna
B. In series with the station's ground
C. In parallel with the push-to-talk line and the antenna
D. In series with the power supply cable, as close as possible to the radio
It goes between the transmitter and antenna, in the feed-line, answer A.
Which of the following connections might be used between a voice transceiver and a computer for digital operation?
A. Receive and transmit mode, status, and location
B. Antenna and RF power
C. Receive audio, transmit audio, and push-to-talk (PTT)
D. NMEA GPS location and DC power
The two audio connections, and the PTT line are connected between the radio and the computer, answer C.
How is a computer’s sound card used when conducting digital communications using a computer?
A. The sound card communicates between the computer CPU and the video display
B. The sound card records the audio frequency for video display
C. The sound card provides audio to the microphone input and converts received audio to digital form
D. All of these choices are correct
The sound card sends audio to the radio, and converts received audio to digital form, for decoding to text, etc, answer C.
Which of the following conductors provides the lowest impedance to RF signals?
A. Round stranded wire
B. Round copper-clad steel wire
C. Twisted-pair cable
D. Flat strap
Flat strap has both low DC resistance, and a large surface area, so conducts it RF well, answer D. This includes using to connect ground connections on equipment to earth plates, and these to the ground rods.
Which of the following could you use to cure distorted audio caused by RF current flowing on the shield of a microphone cable?
A. Band-pass filter
B. Low-pass filter
D. Ferrite choke
A ferrite core or clip-on ferrite may help, answer D.
What is the source of a high-pitched whine that varies with engine speed in a mobile transceiver’s receive audio?
A. The ignition system
B. The alternator
C. The electric fuel pump
D. Anti-lock braking system controllers
This is from the alternator (the generator which charges the battery and powers the car's electrical systems), answer B. A filter consisting of an inductor and capacitors can help filter this out.
Where should the negative return connection of a mobile transceiver's power cable be connected?
A. At the battery or engine block ground strap
B. At the antenna mount
C. To any metal part of the vehicle
D. Through the transceiver’s mounting bracket
The negative line from the radio should go to the negative of the battery, or the ground point near the battery, answer A.
T4A12, a variation on T4A10, but with the whine on the transmitted audio, jokingly called the "remote tachometer", removed.
What may happen if a transmitter is operated with the microphone gain set too high?
A. The output power might be too high
B. The output signal might become distorted
C. The frequency might vary
D. The SWR might increase
To high a microphone gain setting can cause the transmitted audio to become distorted, answer B. That over-deviation or spattering could put a signal at the band-edge, outside the band; or that excessively asymmetrical modulation could put the envelope of a signal beyond band specific power limits are the grain of truth behind the third and first answers.T4B02=
The keypad or VFO dial, answer A, are generally two ways to enter or select frequency. AFC is an old drift compensation system.
What is the purpose of the squelch control on a transceiver?
A. To set the highest level of volume desired
B. To set the transmitter power level
C. To adjust the automatic gain control
D. To mute receiver output noise when no signal is being received
It mutes the noise and hash the radio emits when there is no signal.
What is a way to enable quick access to a favorite frequency on your transceiver?
A. Enable the CTCSS tones
B. Store the frequency in a memory channel
C. Disable the CTCSS tones
D. Use the scan mode to select the desired frequency
Store the favourite frequency in the radio's memory, answer B.
Which of the following would reduce ignition interference to a receiver?
A. Change frequency slightly
B. Decrease the squelch setting
C. Turn on the noise blanker
D. Use the RIT control
Turning on the noise blanker (NB) reduces impulse noise, like vehicle ignition noise, and perhaps electronic injector related noise, answer C.
Which of the following controls could be used if the voice pitch of a single-sideband signal seems too high or low?
A. The AGC or limiter
B. The bandwidth selection
C. The tone squelch
D. The receiver RIT or clarifier
The RIT or clarifier adjusts only the receiver, without affecting the transmitter, answer D. Some radios allow the RIT to be set for the one station in a net who is off channel, then switched in and out as needed.
What does the term “RIT” mean?
A. Receiver Input Tone
B. Receiver Incremental Tuning
C. Rectifier Inverter Test
D. Remote Input Transmitter
It is B, Receiver Incremental Tuning, for adjusting for apparent errors on the transmit frequency of other stations.
What is the advantage of having multiple receive bandwidth choices on a multimode transceiver?
A. Permits monitoring several modes at once
B. Permits noise or interference reduction by selecting a bandwidth matching the mode
C. Increases the number of frequencies that can be stored in memory
D. Increases the amount of offset between receive and transmit frequencies
It allows appropriate filters to match the mode, and so reduce noise and interference, answer B.
Which of the following is an appropriate receive filter bandwidth for minimizing noise and interference for SSB reception?
A. 500 Hz
B. 1000 Hz
C. 2400 Hz
D. 5000 Hz
2400 Hz (2.4 kHz) is the best option, answer C. Your radio may have slightly different figure, such as 2.3 kHz.
Which of the following is an appropriate receive filter bandwidth bandwidth for minimizing noise and interference for CW reception? A. 500 Hz
B. 1000 Hz
C. 2400 Hz
D. 5000 Hz
CW is narrow, so a filter of 500 kHz us used, answer A. DSP (digital) filters can certainly can be tighter.
What is the function of automatic gain control, or AGC?
A. To keep received audio relatively constant
B. To protect an antenna from lightning
C. To eliminate RF on the station cabling
D. An asymmetric goniometer control used for antenna matching
It keep the receiver audio fairly constant, despite variations in the signal level, answer A.
Which of the following could be used to remove power line noise or ignition noise?
B. Noise blanker
C. Notch filter
D. All of these choices are correct
This is the noise blanker, answer B. These devices reduce impulse noise.
Which of the following is a use for the scanning function of an FM transceiver?
A. To check incoming signal deviation
B. To prevent interference to nearby repeaters
C. To scan through a range of frequencies to check for activity
D. To check for messages left on a digital bulletin board
The scan can cover either a range of frequencies, or a group of repeater or other memories, to find active ones, answer C.
On to: Operating 4
You can find links to lots more on the Learning Material page.
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Written by Julian Sortland, VK2YJS & AG6LE, February 2018.
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