see also:

• hand crank torch radios for disasters and hiking
• bushwalking in Australia
• navigation management for hikers
• getting a weather forecast when camping or off-grid

• there are a variety of radio devices available depending upon needs:
  • receive-only type devices:
    • portable battery operated radios
    • Software Defined Radio using laptop and a USB radio dongle with special software and an antenna
  • receive and transmit (transceiver) radios
    • UHF CB radios (no licence needed)
    • higher power rated transceivers which need radio licences to use
• for those going off-grid or for when the internet / mobile phone system goes down such as extreme weather events (strong winds, floods or bushfires knocking out the local electricity grid) it is nice to have other options such as radio which does not rely upon local infrastructures
• radio may be the ONLY way of communicating to the outside world in a disaster
• effect of solar storms on SW radio:
  • in general, SW reception is best in periods when solar activity cycle is at its peak due to a longer term strengthening of the F layer in the ionosphere which the SW bounces off EXCEPT when there is an actual solar storm hitting earth.
  • solar storm activity increases the density of the ionosphere and whilst this will improve reflectivity from the F layer, but it also increases the density of the D layer through which the shortwaves must pass TWICE hence a solar storm hitting earth will generally cause a short-wave fadeout (SWF) or sudden ionospheric disturbance (SID) especially at lower frequencies (especially 5MHz which may be totally blocked, while a moderate effect may be on the 10MHz region where most international broadcasts occur).
  • These Fadeouts mostly have a rapid onset of a few minutes as solar storm hits and a slower recovery lasting perhaps an hour although this is highly variable. The high frequencies (eg. 20MHz) are the last to be affected and the first to recover.
  • NOTE: the HF circuit is affected ONLY if there is an ionospheric reflection point for the signal in the sunlit hemisphere - it will not occur if that reflection point is in the dark. ¹⁾
    • one can check for current SWFs here: https://www.sws.bom.gov.au/HF_Systems/6/2/1

• AM radio
  • amplitude modulation
  • the amplitude (strength) of the radio carrier wave is varied by the modulation signal
• FM radio
  • frequency modulation
  • the frequency of the radio carrier wave is varied by the modulation signal
• FSK radio
  • frequency shift keying
  • used in wireless digital devices to transmit digital signals
  • the frequency of the carrier wave is shifted periodically between two frequencies that represent the two binary digits, 0 and 1, to transmit a sequence of bits.
• OFDM radio systems
  • orthogonal frequency division multiplexing
  • a family of complicated digital modulation methods very widely used in high bandwidth systems such as WiFi networks, cellphones, digital television broadcasting, and digital audio broadcasting (DAB) to transmit digital data using a minimum of radio spectrum bandwidth.
  • has higher spectral efficiency and more resistance to fading than AM or FM.
• sending images as audio signals to create faxes
  • facsimile involves scanning the image and encoding that information.
  • that encoding is transmitted in the form of audio tones which are within the usual voice frequencies and hence can be readily transmitted with either Frequency Modulation (FM) in VHF or UHF bands or Single Sideband for HF bands
  • a computer connected to the receiver's audio out with appropriate software can then decode the audio into a visual image file - usually a GIF.
  • this is often used for weather maps

• the radio spectrum is divided into 12 bands including

• 100-519kHz
• transmitters require a tall radio mast and carrier frequencies are exact multiples of 9 kHz;
• used for broadcasting only within ITU Region 1 including Europe, Russia, Nth Africa
• long-wave signals can travel very long distances up to 1000s of kms

• 300 – 3000 kHz with wavelength of 1000–100m
• transmitters require a tall radio mast
• in this band the signal to noise ratio is determined by atmospheric noise not receiver antenna size and thus radio receivers can use small ferrite rods for this band
• mostly used for AM radio broadcasting (usually 526.5 kHz to 1606.5 kHz), navigational radio beacons, maritime ship-to-shore communication, and transoceanic air traffic control.

• 3 – 30 MHz with wavelength of 100–10 m
• most transmitters use AM mode and all use UTC time
• best listening is usually at night pending path of the radio waves
• Single Side Band (SSB) is used by hams and many utility stations and for Morse Code (CW)
  • set radio to SSB, LSB (lower), USB (upper) or BFO (beat frequency oscillator) to access these
• radio waves in this band can be reflected back to Earth by the ionosphere layer in the atmosphere – a method known as “skip” or “skywave” propagation – these frequencies are suitable for long-distance communication across intercontinental distances and for mountainous terrains which prevent line-of-sight communications
• maximum usable frequency regularly drops below 10 MHz in darkness during the winter months, while in summer during daylight it can easily surpass 30 MHz.
• when all factors are at their optimum, worldwide communication is possible on HF.
• most common antennas in this band are wire antennas such as wire dipoles and the rhombic antenna, and for receiving, random wire antennas are often used.
• used by:
  • international shortwave broadcasting stations (3.95–25.82 MHz) - see http://www.swling.com, http://www.ShortwaveSchedule.com
    • 120m tropical band 2.3-2.495MHz
    • 90m tropical band 3.2-3.4MHz
    • 75m tropical band 3.9-4.0MHz shared with Nth American amateur HAM radio 80m band
    • 60m tropical band 4.75-5.06MHz
    • 49m main band 5.9-6.2MHz
    • 41m 7.2-7.6MHz shared with amateur HAM radio 41m band
    • 31m most heavily used band 9.4-9.9MHz
    • shorter bands down to 11m (25.6-26.1MHz which may be very occasionally used for local digital radio Mondiale DRM broadcasting)
  • aviation communication
  • government time stations
  • weather stations
  • Global Maritime Distress and Safety System (GMDSS) communication
  • some radio frequency identification (RFID) tags utilize HF
  • amateur HAM radio see http://www.arrl.org
    • USA Amateur radio bands
    • with Australian amateur licences, you can only use these frequency bands: 3.5, 7, 14, 21, 28, 52, 144, 430, 1240, 2400 and 5650 MHz
      • on passing your Foundation exam and getting a licence you will have your own call sign and frequency allocation, and then you pay an annual fee to renew the licence
      • see also: Wireless Institute of Australia
      • most amateurs transmitting outdoors will operate mobile from a motor vehicle on 2 metre and/or 70m cm bands but also often on HF bands where more sophisticated antennas and tuning devices are required. This requires an appropriately powered transceiver (the usual 100W may be too power hungry), an adequate portable power supply for the duration of use, and make sure the antennas meet the conflicting demands of efficiency and portability and must ensure that all spares and support material are provided. Antennas for HF bands are usually dipoles or long wires strung between trees or, if you are in a treeless desert, laid along the ground.
  • citizens band services (generally 26-28 MHz)
• see also: https://en.wikipedia.org/wiki/Shortwave_radio

• 30 – 300 MHz with wavelength of 10–1 m
• VHF is the first band at which wavelengths are small enough that efficient transmitting antennas are short enough to mount on vehicles and handheld devices
• VHF signals propagate under normal conditions (excluding mountainous areas) as a near line-of-sight phenomenon:
  • approximate line-of-sight horizon distance in kilometers = sqrt(12.746 x antenna height in metres)
• used for:
  • Digital Audio Broadcasting (DAB) radio (channel blocks 9A, 9B and 9C)
  • FM radio broadcasting (88.1-108.1MHz)
  • television broadcasting (VHF Band I was used for the transmission of analog television)
  • two-way land mobile radio systems (emergency, business, private use and military)
  • air traffic control (118-137MHz)
  • long range data communication up to several tens of kilometers with radio modems
  • amateur radio (50-54MHz 6m band and 144-146MHz 2m band)
  • Radionavigation 60: 84–86 MHz
  • Fixed Maritime Mobile: 130–135.7 MHz
  • Fixed Aeronautical radio navigation: 160–190 MHz
  • Broadcasting Aeronautical Radionavigation: 255–283.5 MHz
  • Aeronautical Radionavigation AUS 49 / Maritime Radionavigation (radiobeacons) 73: 315–325 MHz

• 300 – 3000 MHz with wavelength of 100–10 cm
• propagate mainly by line of sight
• they are blocked by hills and large buildings although the transmission through building walls is strong enough for indoor reception.
• atmospheric moisture reduces, or attenuates, the strength of UHF signals over long distances, and the attenuation increases with frequency.
• occasionally when conditions are right, UHF radio waves can travel long distances by tropospheric ducting as the atmosphere warms and cools throughout the day.
• radio repeaters are used to retransmit UHF signals when a distance greater than the line of sight is required.
• antennae can be 2.5-25cm long and the short wavelengths also allow high gain antennas to be conveniently small.
• used for television broadcasting, cell phones, satellite communication including GPS, personal radio services including Wi-Fi and Bluetooth, walkie-talkies, cordless phones, CB radios
• UHF radar band are frequencies between 300 MHz and 1 GHz plus the L band between 1 and 2 GHz and the S band between 2 and 4 GHz
• in Australia:
  • UHF citizens band (Land mobile service): 476–477 MHz consisting of 80 channels:
    • all communications on every channel are public - anyone can hear and join in if they are in range
    • legally restricted UHF channels
      • Channel 5 and 35: are the designated emergency channels and are not to be used except in an emergency.
      • Channel 11: is the ‘call channel’ and is only to be used for initiating calls with another person, you should quickly organise another vacant channel to continue your discussion on.
      • Channel 22 and 23: are only to be used for telemetry and telecommand, packet data and voice transmission are not allowed
      • Channel 61, 62 and 63: are reserved for future allocation and transmission on these channels is not allowed.
    • accepted CB radio use
      • Channel 10: 4WD Clubs or Convoys and National Parks.
      • Channel 18: Caravanners and Campers Convoy Channel.
      • Channel 40: Australia Wide road safety channel used primarily by truckies and oversized load pilot vehicles.
      • Channels 9, 12-17, 19-21 24-28, 30, 39, 49-60, 64-70, 79 and 80: General chat channels, simplex use.
  • UHF TV 503 - 694 MHz
  • fixed point-to-point Link 450.4875 - 451.5125 MHz
  • land mobile phone service 457.50625 - 459.9875 MHz
  • mobile satellite service: 406.0000 - 406.1000 MHz
  • Wi-Fi operates at 2412 MHz-2484 MHz
  • Bluetooth 2402-24800 MHz

• 3 and 30 gigahertz (GHz)
• small wavelength allows them to be directed into narrow beams via parabolic dishes hence often used for data links
• propagate solely by line of sight;
• create strong reflections from metal objects the size of automobiles, aircraft, and ships, and other vehicles hence used in radar

• NOT useful for emergency communications due to limited coverage
• generally not worth carrying while hiking, except for group management purposes
• they are popular with 4WD convoys and for groups of hunters
• these generally are rated for line of sight coverage
• CB UHF uses frequencies around 27MHz and now has 80 channels available (used to be only 40), in Australia:
  • channel 8: 27.055MHz highway channel
  • channel 9: 27.065MHz emergency channel
  • channel 11: 27.085MHz AM call channel
  • channel 16: 27.155MHz LSB call local
  • channel 35: 27.355MHz LSB call DX
• 5W is the most powerful you can usually buy and generally will get you up to 17km line of sight but they are bigger, heavier (almost 1kg each), use more battery power than 2W versions
• you can also get UHF radios with GPS capability such as:
  • the Garmin Rino 750 - this can show each party with such a device the location of other party members whilst allowing 5W UHF radio communication up to 32km line of sight, and a longer battery life than most smartphones especially in cold weather, plus it is USB chargeable so a USB power pack will allow extra usage. Note though that topographic maps are an extra cost ($A99-199) and must be purchased separately for EACH device, and map updates are not free!

• similar to CB radio but different bands
• in the USA, GMRS is allotted 30 frequency channels in the vicinity of 462 MHz and 467 MHz. They are divided into 16 main channels and 14 interstitial channels
  • requires GMRS licence but usually no exam is needed (unlike HAM radio licences)
• in Australia, UHF CB radio fulfils this use

• NB. HF requires a different antenna (and potentially, attachment to the AirSpy Spyverter to access frequencies < 35MHz) to VHF/UHF and thus you either need a dongle with dual antenna inputs or you need a manual low-loss coaxial switch.
• use a USB dongle (with analog-digital converter) to connect to a computer and to a dipole antenna
  • AirSpy Mini or Airpsy R2 plus Spyverter
    • see https://www.youtube.com/watch?v=50NdrHLWcNc
  • SDRplay
    • https://www.strictlyham.com.au/browse-by-type/receivers/sdrplay-rsp-1568#.YRkZm98RVhE
  • RTL-SDR Blog V3 R820T2 RTL2832U 1PPM TCXO HF Bias Tee SMA Software Defined Radio with Dipole Antenna Kit
  • see https://www.rtl-sdr.com/review-airspy-vs-sdrplay-rsp-vs-hackrf/
• requires special software such as:
  • Airspy
  • SDRuno
• see Youtube articles:
  • The Coolest Radio You've Probably Never Heard Of

• may be the only communication options if the internet and satellite comms go down as with a major solar storm, major disaster such as bushfires/floods or IT warfare
• for campers out of mobile phone coverage range, in addition to keeping in contact with local and nationwide / global news, you can access weather including weather faxes (wefax) of weather maps (just needs audio cable from radio to your laptop and software to decode the fax)
• avoid cheap models
• good models are:
  • Tecsun H-501
    • stereo speakers which can be used via USB as PC speakers
    • microSD card slot to play music
    • 1kg; two 18650 lithium batteries, with separate charging capability.
    • $AU490
  • Tecsun PL-990 High Performance Shortwave Radio
    • seems it is as for Tecsun PL880 but much lighter (620g) and adds:
      • microSD card slot 128Gb to play music files
      • much improved SSB reception
      • superb FM reproduction
      • bluetooth
    • $AU475
  • Tecsun PL880
    • one USB chargeable lithium battery
    • best sound for the era but bettered by Tecsun's 2020 models
    • covers the entire shortwave range (100-29999KHz), Longwave, FM and AM broadcast bands
    • 1.5kg
    • $AU275
  • C Crane CC Skywave Shortwave Portable Travel Radio
  • Eton Grundig Satellit 750 Ultimate
    • no battery, needs 6V input
    • taps into the aircraft band from 118 to 137MHz but unfortunately lacks the weather frequencies, making it unsuitable for an emergency radio that receives NOAA stations.
  • Sangean ATS-909X World Band Receiver
    • No NOAA (weather) and aircraft bands

• usually use a 100W transceiver
  • ICOM IC-7300
  • YAESU FTDX-10

• eg. Yaesu FC-40

• eg. ICOM IC-AH710 HF Broadband Folded Dipole - 80 Feet Long - 150 Watts

• power supply
• microphone
• headset
• cables
• line filters may be needed