On Tue, 1 Jul 2003, Robert Ussery wrote: > > ----- Original Message ----- > From: "Bill Swingle" <[EMAIL PROTECTED]> > > > >>So, if I get the gist of this right, why don't we all use AM instead? > > That is a good question. The simple answer is that FM sounds "better" to > > the average pilot. Thus the market spoke its preference. Manufacturers > > build accordingly and there aren't many Tx's on AM. Certainly not the > > models that we're interested in purchasing. > > Mightn't it also have to do with the fact that FM might (I don't have any > experience to verify this, just theory :O) ) have slightly better range > under noisy conditions? > My reasoning goes like this... > With AM, the pulses are a series of ONs and OFFs. Thus, with the very low > level signals present at near maximum range, it becomes very hard to > distinguish a true ON from spurious background noise, and a true OFF may be > hidden by background noise. > With FM, on the other hand, the pulses are sent by sending an ON on one > frequency and an OFF on another. Thus, even with the very low signal levels > at near maximum range, as long as the ON frequency can be distinguished from > the background noise, its level doesn't matter. Ditto for the OFF frequency. > Faulty logic, or semi-valid reason? >
You are right. AM is much more easily interfered with due to noise because the amplitude of the desired signal and the noise signal are effectively added together in the front end of the receiver. It is this combined amplitude envelope that is demodulated by the receiver and that represents the information in the radio signal. FM, on the other hand, is normally a constant amplitude signal with a varying frequency (or phase), which contains the information in the signal. Noise changes the frequency (or phase) of a radio signal much less than it does its amplitude. RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
