On Fri, Mar 10, 2006 at 11:08:42AM -0500, Rick Eckel wrote: | Hmm..... Of course this is true when all are speaking in the same | frequency range. But how about if all the other conversations are | being held above 20khz or below 20hz??
Yes, whispered voices aren't the best analogy, as they all use the same frequency range. But consider somebody near you speaking in a low voice, as you try to understand somebody far away speaking in a high voice -- the low voice will make it harder to understand the weaker high frequency voice. However, in this case, the confusion happens in our brain, not our ear. Our ears really don't work that much like a typical radio receiver. | Does sheer power on other frequencies swamp the front end of a | receiver? Yes. | Shouldn't we see more evidence of this at the launch area? The reason that we don't is that all the signals are of similar strengths, since all the pilots are near to each other. For desense to occur, the signals don't even have to be in the same band. For example, in my car the FM radio (88-108 MHz) signal gets noticibly quieter when I transmit on my 144 MHZ ham radio. However, the effect is much much stronger when the signals are very close to each other, as they would be with two R/C TX's, or a R/C TX and a pager tower (possibly with hundreds of watts) also in the 72 MHz band. Exactly how much a RX is affected by desense and how close the other signal has to be depends on it's design. Unfortunately, our gear is generally made to be small and cheap, and so it's difficult to add too much protection. As for PPM vs. PCM, PCM uses exactly the same sort of RF stage as PPM -- all that differs is what the signal looks like and how it's decoded. If you've lost control with PPM, you'll also have lost control with PCM, it's just that PCM should handle the loss of control better (going to failsafe or position hold rather than random glitching.) -- Doug McLaren, [EMAIL PROTECTED] All theoretical chemistry is really physics; and all theoretical chemists know it. 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. Email sent from web based email such as Hotmail and AOL are generally NOT in text format
