```Hi John, Alan, Mike, Rik and all, ```I remember hearing slow QSB on the transmissions of G2AJV (when I was in GW) and GW4ALG, both at about 300km. They both used loops and I have not heard QSB at less than 450km with Marconi antennas. ```I can confirm that Roger, G2AJV, had a lot of QSB while othere G's at about the same distance (but using verticals) had no QSB. ```One point may be polarisation: While the groundwave must have vertical E-field and transverse H to propagate, a skywave from above can have two independent polarisations of its horizontal magnetic field (and no E-field over conducting ground). We could surely think about re-using bandwidth by polarisation multiplexing ;-) In a coordinate system with z pointing vertical and x towards the receiver, the skywave of a vertical Tx antenna can be received by its Ez and Hy fields. The same would apply for a Tx loop oriented to the maximum (ie loop-plane in x-z) or a horizontal x-dipole. In the minimum orientation (ie in y-z), these would produce only Hx at the receiver and be undetectable by a vertical. And in the in-between case of near-minimum orientation, the skywave would be preferred and fading emphasized. ``` But there is one thing that I never really understood : Even if a (transmitting) loop produces a lot of 'steep angle' radiation a vertical antenna (for receiving) should be rather insensitive for the incoming 'steep angle' signal. One would expect to notice the QSB only with both TX and RX side are using loops. But I could notice the QSB with a vertical as RX antenna. If the reciprocal principle works then any antenna that can receive 'steep angle' transmission should also transmit at these angles. ``` 73, Rik ON7YD Yes, even though theoretically a path may be non-reciprocal at a given instant due to Faraday rotation in earth's field, on a long-term average the swapping of Rx and Tx antennas should give equal results. For 300km separation, the elevation would be around 35 deg, low enough for a vertical to be effective. How about that possible short-term non-reciprocity: Apparently it is common in moonbounce work, but can it really be observed at LF? As a simple experiment, one could (perhaps automatically) transmit periodic signal reports in a fading situation, and look for discrepancies at the other end. ```Regards Markus, DF6NM ```