[HCARC] Non-reciprocal paths via the ionosphere at HF

Wed Nov 21 15:53:03 EST 2018

Howdy all,

Here are a few additional bits of information relative to this subject.

First, the referenced document is "Ionospheric Radio Propagation" by 
Kenneth Davies.  He was with the Central Radio Propagation Laboratory 
which used to issue propagation predictions for the US government.  
Perhaps some of you remember the HF propagation charts which were issued 
by CRPL.  Eventually they were able to develop a set of documents which 
you could use to predict HF propagation between any two points for any 
sunspot number.  The final step was the software program VOACAP which 
many amateurs still use.  The original publication date of the book was 
1965.

The challenge in modeling/predicting/understanding ionospheric 
propagation is the ionosphere is a plasma embedded in a magnetic field.  
The ionosphere is neither homogeneous nor isotropic.  Any propagating 
electromagnetic (EM) wave can be can be broken down into 2 orthogonal 
components.  We are all familiar with right and left circular 
polarization and vertical and horizontal polarization.  These are 
examples of pairs of orthogonal polarizations.  In the ionosphere, the 2 
natural orthogonal polarizations are Ordinary (O) and Extraordinary (X) 
which are elliptical polarizations.  When an EM waves enters the 
ionosphere it is resolved into the O and X components.  What makes life 
interesting is these two components follow different paths through the 
ionosphere.  as a matter of fact at frequencies near the MUF the X wave 
may not even be returned to the ground but go into space.  If they both 
are returned, since they were in the ionosphere for different times due 
to their different paths the polarization of the EM wave at the distant 
point may be different than it was when transmitted.  The poplarization 
change for the 2 directions is in opposite directions.  I believe that 
is where most of the non-reciprocity comes from.

EM waves are not generally reflected as if by a mirror.  The reflection 
height is called the "virtual Height".  The EM wave never reaches that 
point but follows a curved path well below that point.  The only 
exception is sporadic-E where the ionospheric layer is dense and thin.

By the way I've never heard a ham try to justify his need for a linear 
on non-reciprocal propagation.  The reason is he wants to be able to 
bust pileups!  Most non-reciprocal propagation on the hand bands is 
caused different power levels and/or different operator abilities on the 
two ends.

If anyone is seriously interested in the whys and wherefores, I suggest 
"Radio Waves in the Ionosphere - the Mathematical Theory of the 
Reflection of Radio waves from Stratified Ionised Layers" by K. G. 
Budden, 1961.  He is British - "ionised" is spelled correctly!  Be 
prepared - Reading and understanding Budden requires math beyond Calculus.

If you have any questions send them along

Kerry

On 11/21/2018 10:15 AM, Gary Johnson wrote:
> Starr – excellent article for the Static.
> Gary J
> NA3VY
> *From:* Ken Nichols
> *Sent:* Tuesday, November 20, 2018 10:37 PM
> *To:* STXDXCC at groups.io
> *Subject:* [STXDXCC] #Contest #DX Non-reciprocal paths via the 
> ionosphere at HF
> As suggested at the meeting tonight, here’s a posting I put on 
> KARSnews at groups.io earlier today.   Actually it probably has more 
> relevance here than on that group.
> ——————
>
>     Here’s an interesting post from a FlexRadio forum.  It’s from a
>     discussion about why hams justify the need for a linear amplifier
>     sometimes. The discussion was focused on how the RF path between
>     two stations is different depending on which station you’re at.
>     Take note of the link to a very interesting free book from the
>     government.
>     -Ken-  KD3VK
>     ——————
>     Noni-reciprocal paths via the ionosphere at HF
>
>     During a discussion on Pedersen rays at a recent CAKE meeting it
>     was claimed these were “asymmetrical” paths and an explanation was
>     needed.
>
>     We all know that much of our hobby depends on the ionosphere to
>     return our transmitted signals back to earth and we may tend to
>     think in terms of mirror-like reflections. Nothing could be
>     further from the truth as the ionosphere is an unstable mix of
>     charged particles and gases.It has both regular and irregular
>     behavior.
>
>     Although the ionosphere was key to commercial world-wide radio
>     communication from around the 1930s the great deal of knowledge
>     accumulated was practical rather than scientific. The science of
>     the Ionospheric began sometime around the 1950s with the invention
>     of atmospheric sounders. Scientific studies were intensified in
>     the 1960s for security reasons when understanding propagation in
>     high northern lattitudes became especially important. Hang on I
>     will answer the question soon HI
>
>     In 1967, NATO held a conference on Ionospheric communications with
>     a focus of the Arctic and the conference proceedings has a section
>     on HF entitled The difference in levels of signals travelling in
>     opposite directions. The following three statements were selected
>     from that section:
>
>     1. Paths between two antennas can be non-reciprocal but this is
>     NOT due to differences in ray path attenuation or phase. On the
>     basis of ray theory these are the same for signals travelling in
>     either direction.
>
>     2. The reciprocity or non reciprocity arrises only because of
>     interaction of the upward or downward waves with the antennas at
>     the ends and the earths magnetic field.
>
>     3. A reciprocal path is formed between linearly polarized antennas
>     (most amateur antennas) if they are both polarized in, or
>     perpendicular to, the earths magnetic field otherwise the path can
>     be non-reciprocal.
>     The section reached the conclusion that “most ionospheric paths
>     are non-reciprocal with the result that there can be large
>     instantaneous differences in the levels of signals travelling in
>     opposite directions.”
>     To go beyond that statement and understand the mode and practical
>     implications one needs to look into the phemomena of the
>     ionosphere converting an incoming plane polarized wave into two
>     outgoing circularly polarized waves known as O ordinary and X
>     extraordinary.
>
>     Ron W6WO
>
>     See Reference Also
>
>     https://www.gpo.gov/fdsys/pkg/GOVPUB-C13-fb3928334c2e900ed6a1cc1312e7db64/pdf/GOVPUB-C13-fb3928334c2e900ed6a1cc1312e7db64.pdf
>
>     Download the NIST Book from the link above
>     The HF Radio Ionosphere Sounders Studies
>
>     Prove the paths for Gray line DX are asymmetrical
>
>     On HF and not equal from both Directions especially
>     On Multihop and Sporadic E propagation !
>
> Free Book while it lasts (budget constraints) from
> the NIST Library Reference Link above !!
>
> Hams love free stuff !!!
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