Most short-term fading on HF is caused by polarization rotation of the incoming signal. Because of effects caused by the earth's magnetic field, the ionosphere twists signal polarization to greatly varying degrees, so the main incoming signal goes through cross-polarization nulls on the receive antenna at times, and that's when it fades. When that happens, weaker signal paths become significant, and the phase shift caused by the path-time differences causes severe selective fading.
A circularly-polarized antenna reduces this problem significantly. However, the incoming signal tends to have an elliptical or circular component, so the correct circular 'sense' is important - and this changes, depending on signal path and time of day. Even so, simply connecting a vertical and a horizontal antenna together will often result in noticeably reduced fading. See "CIRCULAR POLARIZATION ON HF" AM Press/Exchange, Issue #116, December, 1995 www.amfone.net/AMPX/116.htm http://www.bruhns.us/CP_on_HF/CP_on_HF.html Bacon, WA3WDR ______________________________________________________________ AMRadio mailing list List Home: http://mailman.qth.net/mailman/listinfo/amradio Partner Website: http://www.amfone.net Help: http://mailman.qth.net/mmfaq.html Post: mailto:[email protected] To unsubscribe, send an email to [EMAIL PROTECTED] with the word unsubscribe in the message body.
