![]() ![]() Much like a page printed out on your printer. Consider a long rectangle placed vertically ![]() at the adjacent channel spacings we would want an attenuation of say -30 dB where the signal is reduced to. In an idealised receiver we would want our signal to have a shape factor of 1:1, i.e. Sorry if this is going to be long but you MUST understand these basic principles. This is a bit like singling one tree out of among a lot of other trees in a pine tree plantation. Clearly this signal falls well within the -3dB points of 10 Khz and suffers no attenuation (reduction in value). These figures are of courseįor illustrative purposes only. etc and our signal, as transmitted, is plus / minus 4Khz then our 550 Khz channel signal extends from 546 Khz to 554 Khz. radio band where the spacing is say 10 Khz e.g. If our signal sits in a channel in the a.m. where in voltage terms, the signal is reduced to. When we discuss bandwidth we mostly speak in terms of the -3dB points i.e. Let's consider this in some detail because it is critical to all receiver designs. filters of this type is that the filter receives one signal and one signal only. Finally a further disadvantage (c) was the shape factor could only be quite poor. band 1650 Khz, the received bandwidth was still 1650 / 55 or 30 Khz. As an example - if the circuit design Q was 55 at 550 Khz the received bandwidth would be 550 / 55 or 10 Khz and that was largely stages had to track one another and this is quite difficult to achieve technically, also (b) because of design considerations, the received bandwidth increases with frequency. The principle disadvantages were (a) all r.f. stages simultaneously tuned to the received frequency before detection and subsequent amplification of the audio signal. (tuned radio frequency) receiver was among the first designs available in the early days when means of amplification by valves became available. If you are unfamiliar with the design then check out the crystal set page.Ģ. The first receiver built by a hobbyist is usually the plain old crystal set. What are the basic types of radio receivers? basic crystal setġ. Unfortunately the increased cost of receiver complexity forbids this but it certainly is feasible - see Single Side Band. This spacing could be reduced and nearly twice as many stations accommodated by deleting one side band. radio stations are spaced 10 Khz apart (9 kHz in Australia) e.g. For sophisticated receivers one side band can be eliminated. For very simple receivers such as a cheap transistor radio we only require the original plus either one of the side bands. the original 900 Khz (the carrier) plus and minus the modulating frequency which are called side bands. To suit our discussion and keep it as simple as possible we will have the transmission modulated by a 1000 Hz or 1Khz tone.Īt the receiving end 3 frequencies will be available. This frequency will be very stable and held to a tight tolerance. For example consider a local radio station transmitting on say 900 Khz. radio however.įirstly because of the modulation process we generate at least two copies of the intelligence plus the carrier. There are three distinct disadvantages to A.M. Industries grew up manufacturing radio parts, receiver manufacturers, radio stations, news agencies, recording industries etc. This discovery spawned whole new industries and revolutionized the world of communications. This is called modulation and obviously in this case amplitude modulation or A.M. This process could be easily reversed by simple means at the receiving end by using diode detectors. then real intelligence could be conveyed e.g. Then it was discovered that if the amplitude (voltage levels - plus and minus about zero) could be controlled or varied by a much lower frequency such as A.F. This was the only form of radio transmission until the 1920's and only of use to the military, commercial telegraph companies and amateur experimenters. region.Ĭommunication was by way of morse code much in the form that a short transmission denoted a dot (dit) and a longer transmission was a dash (dah). In the early days of what is now known as early radio transmissions, say about 100 years ago, signals were generated by various means but only up to the L.F. What are the basics of AM radio receivers? YOU ARE HERE: HOME > RECEIVERS > AM RADIO RECEIVERS ![]()
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