From: MarkusVester@aol.com
Message-ID: <80.bdc4ee9.285ff881@aol.com>
Date: Mon, 18 Jun 2001 20:36:17 EDT
Subject: LF: Steep skywaves, polarisation, non-reciprocity
To: rsgb_lf_group@blacksheep.org
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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