Is there really such a thing as one way skip?

[AA4PB]

Antennas surely are reciprocal. The perceived difference is again noise related. An inefficient antenna will attenuate the noise about the same as the signal and so the S/N ratio stays the same and the antenna is perceived as receiving okay. On the transmit side, your antenna only attenuates your signal on the other end, not the noise. Of course if you don't have an effecient means to match the antenna to the transmitter then you can't even get the power into the antenna so the transmit situation is even worse.

Provided everything is properly matched, an antenna that is 3dB below a reference antenna on transmit will be 3dB below that reference on receive.

[WB6BYU]

This certainly happens on EME circuits due to polarizaton
rotation, and HF ionospheric paths can be affected
similarly.

I had a QSO with a KH6 once where I had two antennas
available - a long wire and a 2-element yagi.  There
was a pronounced cyclic fade on the path - perhaps once
a minute - and the timing of the fade was different
for the two antennas.  The station at the other end
also observed the signal fades, but the fades at his
end were different than those at my end.  Clearly we
had some sort of "one way propagation", at least at
certain times of the fade cycle.  My guess in this
case was that it was due to polarization rotation.

If so, the effect would probably be less noticable using
a quad than using a yagi:  the quad had only one element
that determines the polarization (since the parasitic
elements respond equally well to any polarization) while
every element on the yagi is polarization specific.
In that case, a signal from the yagi received on the
quad with a 45 degree polarization shift would be
stronger than the other way around.


Also, given that the ionosphere is not a perfect
reflecting surface, there certainly are opportunities
for differences in propagation paths.  Most ionospheric
paths are due to refraction/diffraction instead of
reflection, though the latter is a more convenient
explaination.  I seem to remember calculating some
radar distance corrections for atmospheric refraction,
and the ray tracing algorithms would come up with
different answers depending on whether you went from
the radar to the target or from the target to the radar.  Also remember, if you are using the "angle of
reflection from the water" explaination, that a fish
can see you one direction through the water even when
you are seeing the reflection of the sky when you look
in the lake.

So I suspect there are several different causes of "one
way skip", but the most common are going to be due to
a difference in power or noise/QRM levels, being off
the back of someone's beam, or, "I don't want to work
yet another lousy W6 today."

[KA5S]

I suspect it has to do more with local noise and interference than non-recoprocal skip. Suppose you want to talk to a station who has BPL in his area. You'll hear him, but it's likely he won't hear you.  One way enough?

However, we do use one-way isolators made of a ferrite in a magnetic field; I guess it'd be possible to get a similar, though more diffuse condition, in the ionosphere.

Cortland

[W8JI]

I've made hundreds of thousands of QSO's, and have never seen one way skip that can't be explained by high noise on one end or a poor transmitting antenna or low power on the other end.

I suppose there are rare cases where the MUF might be higher in one direction than the other, but it's very doubtful it is common.

Most of the "one-way-skip" complaints occur when one end of the path has high noise or the stations are very dissimilar.

One key factor is the antenna. Antenna gain has a direct influence on transmitting signal level. Directivity has the major influence on receiving capabilities. Gain and directivity are different, since efficiency does NOT influence directivity. This means, contrary to popular rumor, a very inefficent antenna can make an excellent receiving antenna. At the same time, it might not be worth a hoot for transmitting.

An example is a very low antenna over poor soil, like a Beverage antenna, although even a dipole could fit this catagory.

There are dozens of much more logical and common reasons why "one way skip" occurs than differences of path from A to B than from B to A, although it is still possible.

73 Tom

[W3FHW]

For an explaination of this occurance please read the "ARRL Antenna Book" under "S" for Scatter.

[N6KB]

The short answer to your question is: No, there is no such thing as "one way skip". There is something called "the principal of reciprocity" which says that if there is a path in one direction, with a certain loss, then the path in the opposite direction will have the same loss...

However there are conditions which can make it seem like there is a "one way path". For instance when ever the signal to noise ratio at the output of the receiver at one end is significantly better than at receiver at the other end, this can seem to be "one way skip". There are a number of reasons this could happen, the most obvious being a higher ambient noise level at one end of the path. Another reason could be an antenna at one end of the path that has more gain in the direction of a noise source....

Now suppose that two stations have identical equipment. They are both using an omnidirectional antenna with unity gain with respect to a dipole (a vertical with a perfect ground system) and they are both running 100 watts output, and they both have receivers with identical characteristics in all respects, equal MDS (minimum descernable signal), equal bandwith filters, equal gains all the way through from antenna port to speaker output, and precisely adjusted equally responding S meters. In this situation the signal strength measured at either end, when the opposite end transmits, will be equal. If one station has really high powerline noise, and the other lives out in the boonies and has his own, rf quiet, solar power system, it may seem like there is one way skip. If they carefully analyze the data from their super accurate S meters, they'll figure out that it is not one way skip. It is really just a higher noise level at one station. ...

In the real world even identical model receivers don't work exactly the same, and especially S meters aren't laboratory standards by any means, AND when watching a varying signal, two different people will read it differently anyway. So it may seem like one way skip.

[KC2KCF]

There are some common misconceptions about the reciprocity principle, the most common one is taking it as an absolute truth. The reciprocity principle (which states that path "losses" are the same both ways) is valid only under specific symmetry assumptions.

For ionospheric propagation, these assumptions are not met. Specifically, the interaction of the earth's magnetic field with the charge carriers in the ionosphere makes propagation nonreciprocal. A specific form of this effect (Faraday rotation) is widely used to build microwave isolators (one-way transmission lines). It is worth noting that, while Faraday rotation only affects the polarization, in the ionosphere even the actual signal path differs for both directions.

However, while it IS possible to have "one-way propagation", I suspect that in the vast majority of cases, the reason for apparent one-way propagation lies elsewhere.