Intermediate Licence: Building on the Foundation

| January 19, 2012

Interm_6This brand new revised and updated 6th edition of Intermediate Licence: Building on the Foundation is the latest incarnation of this invaluable book for those seeking to upgrade their Foundation callsign.

Click cover picture to buy this online.

 

Corrections, updates and additional information

Additional material

Corrections to the 6th Edition

Since late 2013 the RSGB has been shipping a revised 6th edition of the Intermediate Licence Book first published in 2011. No corrections to previous editions are now listed.

Revisions to the 2011 edition:

Page 22 – QSL cards (8f.2)
In 3rd paragraph, replace from ‘You should note that anyone can…’ to ‘…can send cards through it.’ with ‘To use the UK Bureau you need to either be an RSGB member or have paid to receive cards but only RSGB members can send cards through it. If you would like details of how the RSGB operates the bureau please visit www.rsgb.org/qsl .

Page 67 – column 2, paragraph 2, replace from ‘FM (VHF or UHF): wavy…’ to ‘…time with engine speed.’ with the following:
“Analogue TV transmissions in the UK have ceased although there will be some analogue TVs with external ‘set top boxes’ still in use for a while. These remaining analogue sets may continue to show some signs of local interference from radio transmissions, electric motors and car iginition systems. Common effects include wavy lines, loss of colour, dotted lines, loss of sound and audio breakthrough.”

Page 70 -Interference from modulation (4e.1)
You may recall from your Foundation studies that it is important to set your microphone gain, TNC, or PC audio output, such that you keep your signals free from distortion and so you do not cause interference to other radio users. Let’s expand on that a little.

In an AM transmitter, excessive audio amplitude will cause ‘overmodulation’. This will cause the modulated signal to become distorted and can make the bandwidth of the signal wider than the usual 6kHz. That would cause interference to other stations on adjacent radio frequencies and make you very unpopular! The same applies to SSB, which is a ‘special kind of AM’ with a bandwidth that is half that of an AM signal; overmodulation will result in a signal that is wider than 3kHz and so have the potential to cause interference to adjacent channels.

In an FM transmitter, the amplitude of your audio frequency will cause the waveform to deviate more than is required; a condition known as ‘overdeviation’. This would cause your signals to be unintelligible and cause interference to other stations on adjacent radio frequencies, which is clearly undesirable and a breach of your licence conditions.

For AM, SSB and FM transmitters, having the microphone gain control, or the PC sound output, set too high can cause the microphone amplifier in the transmitter to produce AF harmonics, making the bandwidth of the audio fed to the modulator much wider than it should be.  This excessive audio bandwidth can also cause overmodulation and/or overdeviation.

These modulation methods are examined in more detail at the Advanced level. At this level it is sufficient to recall that applying excessive audio amplitude or excessive audio bandwidth to a modulator can cause excessive AM bandwidth or excessive FM deviation and that both can cause interference to adjacent radio frequencies.

 

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