What are HF radios?

HF means high-freqency these are radios that use frequencies between 3 MHz and 30 MHz. This webpage will also talk about lower freqencies, it is our focus to show capabilities of these radios even if they got abounded in the name of higher frequencies.
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Basics

Radios are devices that allow for transmission of signals over the air, high freqencies allow for alow wider range of broadcast with lower power. Currently they are utilised by radioamatures, radar system and radio pirates. This types of system gain a lot more from antena than from power of the transmitter.

Antenas

Dipol

Dipols are the most basic kinds of antenas. They are in length half the wave legth. Some cool parameters are that the wideness of the band can be changed by changing the ratio of the cable or if antena is made into a hollow cylindrical shape the ratio of that shape, this lowers the gain of the antena but significantly widens the band. It is Omni-directional in one plane and has a donut like propagation characteristic in the other plane.

Unipole

Unipol works on a similar rule to a dipol antena yet has only one half of it that is half the length of the wave it is made for. Its transmission characteristic is sliglty more to the front (egg shaped) but it is also somewhat more Omni-directional because of no other wing. This allows for the characteristic to recive better in one plane while being silghtly more directional in the other.

Endfed

Endfed is one of the most common in use on lower bands, it does not offer significant gain compared to some antenas but it is Omni-directional, cheap and easy to produce. A good pro of the antena is its ability to work on multiple bands without the need for them to be synchronic to the original band of the antena. It allows easy transport, mostly being made from an un-un or an balun and a wire made with length of the bands in mind. Sometimes it can utilise a antena wire connnecting it to the transreciver as a counterweight

Bazooka

Bazooka is an antena based on a dipol, instead of a transformators for its to wings it uses an antena wire with heavy screens like rg100 or ones with even more screens, it is also akin to a dipol omidirectional and a donut shaped in the other plane, a con of a bazooka its not a compromise antena like endfed meaning it allows for less bands at once but it has a visibly bigger gain and recives alot less noise.

In-phase antenas

In phase antenas are allowing for better directionaly, these are made from a couple of other antenas connected to a same phase. Changing the distance between these antenas changes the direction in which it recives and the gain of it. The gain changes logaritmically with a changes with a square of 2 so the first change will be from 2 to 4 than 8 etc etc.

Modulations

AM DSB and DSB-SC

AM is amplitude modulation which means it modifies the amplitude of the analog audio signal, DSB means it is dual side band - less reach but less interference, added SC means suppresed currier it allows for slightly stronger signal. Both types were used early on in radiocomms and offered in theory longer distance compared to FM but were used on LF and MW which in addicion to AM's ability to be easily interfered caused it to be abounded in most use cases.

AM SSB AND SSB-SC

SSB meaning single side band is a modulation with lesser ability to fix interferance but a lot higher rencity in power, it is only around 3100Hz in width and uses one side of the band like name suggests with it being considered that LSB (lower side band) is used in frequencies bellow 10 MHz and USB (upper side band) is used in freqencies above 10 MHz, diffrence between them is that SC is harder to tune into because of its lack of currier but preffered in radiocomms because of its even better power characteristic.

AM VSB and ISB

VSB Vestigial sideband modulation is now considered archaic since its last common usecase was analogue TV, it was a compromise between SSB and DSB having one side of the band slightly suppresed. ISB Independant sideband is two sides of the band tansmited independantly, its usecases are very rare and far in between.

FM

FM modulation is a very wide topic, starting from it having a wideband and narrowband versions and ending at it having an option of having a text sending coded in. Lets start with the most basic FM: narrowband FM. It is used mostly in radiocomms such us repeaters and voice communicaton on higer bands eg. VHF. It only often has a bandwidth of 10kHz, 12.5kHz, 25kHz, these clasify as narrowband but in radiocomms 25kHz is reffered to as wideband. Yet in FM radio we dont use this type of FM, we use wideband that has a bandwidth of around 200kHz in where we have a pilot around whom there are deviations of up to 75kHz, on which 75kHz is used to transmit audio signal and than we have control signal that tells the receiver should it decode stereo signal data and expect it, or should it see the signal as mono and decode it as such. Over the bandwidth also transmited is a text signal we can recognise from cars telling us what station and music are we listening to, it is called RDS (radio data system).

PM and Digital modulations

FSK

FSK known as frequency shift keying to encode a one or a zero in this keying the freqency shifts slightly, it is fairly simple to code and recive also allowing for some error in freqencies if made well. A fun fact about it is that the use case you may recognise it from is the first internet protocol or what became internet at the very least, protocol used by a modem called "Bell 101" used FSK and allowed for extreme speeds of up to 110bps, we know disapointing. After Bell 101 went out of use 110bps FSK still stuck around in dialup as a protocol used for two routers to establish other protocols they support. In modern times we can still meet FSK, for example on radio waves in a form of a digital modulation called RTTY.

BPSK

BPSK known as Bi-Phase Shift Keying is a digital modulation with phase shifting by 180 degrees with one or zero so that every one has the same phase and every zero has the same phase. The big pro of this modulation is that it can in theory auromatically synchronise making it have no need to listen in for ideal time to recive and lets the reciver not risk any problems with wrong receiving of sent bits.

QPSK

QPSK known as Quad-Phase Shift Keying also called 4PSK is a digital modulation akin to BPSK but made with ability to transmit two bits at forthwith using phases of 0 degrees as 00; 90 degrees as 01; 180 degrees as 10 and 270 degrees as 11. It is a good modulation in cases of very small mesadges as it is as resistant as BPSK to interferance yet twice as fast.

QAM

QAM known as Quadrature Amplitude Modulation is seeing its current uses in DVB and DAB meaning digital video broadcast and digital audio broadcast used in digital TV and radio. It changes both amplitide and phase. QAM starts at QAM 16 able to send 4 bytes, than 32 sending 5 and so on. All the changes are square roots of two with 2^n being able to send n bytes. Full sending campacity of QAM is not used because a couple of bytes are used for correction of mistaked made during sending.

OFDM

OFDM known as Orthogonal Frequency-Division Multiplexing is making use of multiple channels giving an ability of senting multiple signals in one bandwith, it has to use a diffrent frequency out of the signals bandwith for diffrent carriers. It is also used in modern digital TV modulations allowing for one channel to carry multiple programs at once.