On Feb 2, 2011, at 2/2 1:37 AM, Julian, G4ILO wrote: > The most important thing when using PSK modes is not how much power > you are > using, but that the signal is *clean*, with the minimum of IMD > products. And > that is why with a barefoot K3 or any other 100W radio you should > not exceed > about 40W output.
I agree completely with Julian about this. PSK31 is a weak signal mode when conditions are good. How much power you need to use depends on the SNR of your signal at the receiving end. Think about it. A 3 dB difference in your signal can only affect the blocking dynamic range of the receiver by 3 dB. But if your transmit IMD is 6 dB worse (I have seen some "QRP" signals with -25 dBc IMD), you are ruining the band for many more people than just your nearby neighbors who have receivers with poor dynamic range. With the K3, there is no practical difference in transmit IMD between using 20 watts and 50 watts. See the two tables halfway down this page: http://homepage.mac.com/chen/Technical/K3/Digital/digital.html In practice, it is non-productive to run power once your SNR at the receiver is over 0 dB in a 300 Hz noise bandwidth. When there is multipath, PSK31 will not get through no matter how much power you use. Even though RTTY is 3 dB less sensitive than PSK31 when conditions are good, it can still get through even flutter if you have a good SNR at the receiving end (i.e., transmit with more power). PSK31 will not get through flutter no matter how much power you apply. 73 Chen, W7AY ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
