Last Updated on December 2, 2025 by John Berry
There’s a lot to amateur radio. It’s not essential that radio amateurs understand all the core radio communications concepts – but it helps!
Threshold degradation (TD)
There are many reasons why a ham radio station may, on one band or other, suffer threshold degradation (TD). Mostly, TD occurs through added presence of noise. There should be a favourable receiver threshold, but because of noise, it’s degraded. Here’s a definition and how TD, and its parallel, TI, are used.
The Decibel
No discussion about radiocommunications would be complete without a note about the unit used – the decibel, abbreviated dB. I regard Rec. ITU-R V.574-5, Use of the decibel and the neper in telecommunications as definitive. For simplicity I’ve copied here the key applications as they affect my work on other pages on this site.
Chance
When one radio amateur sends a signal to another, there’s a chance that the signal will be received above the threshold of reception. If the signal received is above the threshold of reception, an exchange of voice or data messages may be possible. Chance governs communications. Many amateurs embrace this, and chance gives the well-established concept of ‘DX’ – communications when the chance is low. Read why chance is so significant to radio amateurs.
The Doppler effect
The Doppler effect is ever present in ham radio communications. Sometimes it’s significant and matters. Sometimes it’s insignificant and can be ignored. My focus is on particles and bodies that appear mid-path and reflect radio signals transmitted between two radio amateurs. And for the Doppler effect to be observed, they or the reflecting particles or body must be moving. The Doppler effect must be accounted for.
System value
The system value is the maximum loss between the transmitter output and the receiver input for a given response in the receiver. The system value is fixed for that system technology (comprising modulation and coding). There are differing system values for narrow band FM voice, SSB and each narrow band data mode such as FT8. Here’s how it’s calculated and used.
Path budget
A path budget is as it implies – a currency pot in decibels that you as radio amateur can ‘spend’ in communicating with others. It’s not quoted in monetary terms – though some might argue that the bigger your purse, the greater the available budget and the more likely the rare DX. But that’s another story. The path budget guides the way you choose to spend your System Value, and the benefit you get as a result of choices you make. Here’s how it’s calculated.
Receiver threshold
The threshold of reception is the input to a receiver required to just produce the desired communication result. It is one of the two parameters to calculate the System Value. The receiver threshold improves with reducing transmission bandwidth, exploiting the bandwidth effect. Hence, wideband FM requires significantly more signal compared to FT8, for example. Receiver threshold also improves with data coding. Click for more on receiver threshold.
System noise
Noise reduces the receiver threshold and hence is of great interest to radio hams. To include electrical noise (from the various system components including environment, antenna array, low noise amplifier and feeder) we need to be able to calculate the noise contribution of each component. This is explained here using a cascade calculation to reveal the system noise figure and deduce how the threshold changes.
Data modes
DX – the seeking out of rare amateur stations at vast distance – is a central focus of many radio amateurs. By greatly improving the receiver threshold by up to a factor of 10,000 (40dB), modern data modes materially affect the hobby by making the rare not so rare, and shrinking distances. The outcome of such a revolution has been questioned by many in the hobby. If it all becomes too easy – like shooting fish in a barrel – where’s the fun. Watch the video here and add to the debate.
Antennas
We find two antenna applications in ham radio – antennas that are erected in near-free space, and antennas that are deployed so close to the ground that the antenna and ground are one. The antenna launch angle is given by the elevation of the principal V-plane response; and the gain is given in decibels relative to an isotrope. Both are key in the path budget in calculating the likelihood of communications. Here’s more.
Transmission modes
At the transmitter, information (speech or data) is impressed on a carrier by various means to generate a modulated carrier. The modulated carrier systems or transmission modes used in ham radio are based on three basic schemes – on-off carrier (CW), amplitude modulation (AM), and phase or frequency modulation (FM). This page describes the three and how they have been exploited to yield more complex data systems like FT8.
Core radiocommunications concepts bibliography
Here’s a list of papers, books and the like that have informed the pages about core radio concepts.