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Author Topic: South America propagation question  (Read 388 times)

KM4SII

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South America propagation question
« on: January 04, 2023, 02:59:13 PM »

Hello all,

Hopefully this is an acceptable place to ask this question. Over the years, I have consistently noticed that PY stations often have significant flutter on their signals, especially in the evening. It is most pronounced on 20m, but I recall noticing it on 40m as well. It does not seem to be as prevalent on the higher frequencies though. It sounds similar to the flutter I sometimes hear on over-the-pole paths, but of course, that cannot be the case here.

Has anyone else noticed this? Does anyone more knowledgeable about propagation oddities than myslef know what causes this? It has always puzzled me, and my curiosity got the better of me today  ;D

73
Mason - KM4SII
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K6SDW

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Re: South America propagation question
« Reply #1 on: January 04, 2023, 04:32:13 PM »

KE0OG, the ARRL and QST's new technical editor has a YouTube video explaining propagation...I found it very informative.  Of course, there's always the ARRL's Antenna Handbook...

Abt 1/2 hour ago I worked CX6VM on 20m CW, weak but workable. Antenna here is an EFHW abt 25' in the air and zigzags all around the yard.

GL/73
« Last Edit: January 04, 2023, 04:35:43 PM by K6SDW »
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N1UK

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Re: South America propagation question
« Reply #2 on: January 04, 2023, 06:31:09 PM »

Quote
Has anyone else noticed this?

I am in North Carolina and I can't say that I have not noticed it but I have directional antennas on 20 and 40m and I rarely beam towards South America.  I wonder if you are getting some backscatter as well as a forward path.


73 Mark N1UK
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KH6AQ

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Re: South America propagation question
« Reply #3 on: January 04, 2023, 06:34:10 PM »

I wonder if what you hear is TEP (transequatorial propagation) multipath distortion.

TRANSEQUATORIAL RADIO PROPAGATION

"It was observed that there were two distinctly different types of TEP that could occur:
The first type occurred during the late afternoon and early evening hours and was generally limited to
distances under 6000 km. Signals propagated by this mode were limited to the low VHF band (<60
MHz), were of high signal strength and suffered moderate distortion (due to multipath)."


https://www.sws.bom.gov.au/Category/Educational/Other%20Topics/Radio%20Communication/Transequatorial.pdf
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KM4SII

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Re: South America propagation question
« Reply #4 on: January 04, 2023, 07:23:05 PM »

I wonder if what you hear is TEP (transequatorial propagation) multipath distortion.

TRANSEQUATORIAL RADIO PROPAGATION

"It was observed that there were two distinctly different types of TEP that could occur:
The first type occurred during the late afternoon and early evening hours and was generally limited to
distances under 6000 km. Signals propagated by this mode were limited to the low VHF band (<60
MHz), were of high signal strength and suffered moderate distortion (due to multipath)."


https://www.sws.bom.gov.au/Category/Educational/Other%20Topics/Radio%20Communication/Transequatorial.pdf
That is very interesting, and I would say very plausible as it seems to match up with what I am hearing. I was not aware that TEP could cause such distortion, but that could certainly explain why I never hear such characteristics on signals from stations in, say, YV or HK, but do on signals from QTHs south of the equator.

Quite fascinating! Thank you for the insight.

73
Mason - KM4SII
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KM4SII

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Re: South America propagation question
« Reply #5 on: January 04, 2023, 07:25:54 PM »

Quote
Has anyone else noticed this?

I am in North Carolina and I can't say that I have not noticed it but I have directional antennas on 20 and 40m and I rarely beam towards South America.  I wonder if you are getting some backscatter as well as a forward path.


73 Mark N1UK
I too am located in North Carolina so your observations are especially helpful. If it is indeed multipath distortion as KH6AQ suggested, then perhaps your directionality helps to reduce it. My antennas are all dipoles and delta loops, so not too much in the way of directionality on my end.

73
Mason - KM4SII
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N4UFO

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Re: South America propagation question
« Reply #6 on: January 05, 2023, 02:51:00 AM »

It is most pronounced on 20m, but I recall noticing it on 40m as well.
"It was observed that there were two distinctly different types of TEP that could occur:
The first type occurred  <snip> Signals propagated by this mode were limited to the low VHF band (<60 MHz)"

Quote from: cited link
"The second type of TEP occurred from around 1900 to 2300 hours local time. Contacts were made at
144 MHz, and even very rarely on 432 MHz."

The same possibility occurred to me, but I wondered if TEP could even work on such low frequencies. Reading up, my thought was correct, no, the phenomenon is observed on 10m at the lowest. My experience chasing WPX South American stations... 10m, they seem to be everywhere compared to the other HF bands... would confirm that. (Some summers, seems all there IS on 10m is South America!) And the paper KH6AQ cited even says TEP is pretty much a 10m/6m & up thing...  That said, it may still have something to do with the equator, but not what is traditionally thought of as TEP with the normal telltale sign of TEP being that the two stations are close to equidistant from the equator on either side.

All that said... I am no expert, I can easily be wrong, just commenting on what I have read and observed.  :)
« Last Edit: January 05, 2023, 03:08:13 AM by N4UFO »
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N1UR

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Re: South America propagation question
« Reply #7 on: January 05, 2023, 04:10:15 AM »

Up here in Vermont that is a common occurance on 10 - 20M and I have yagis on these bands.  Here its a combination of direct path vs aural backscatter arriving at slightly different times.  You can tell because the north facing yagi will pick up locals bouncing off it that you wontt hear well when pointed south.  It can make PY and LU almost un copyable on CW at times.

Ed  N1UR
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W4AMP

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Re: South America propagation question
« Reply #8 on: January 06, 2023, 06:37:51 PM »

Exactly. Multipathing flutter. F with signal report.
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