RE: [HamSCI] Digest for hamsci@googlegroups.com - 1 update in 1 topic

[euro.emc.service]

Thanks for sharing, Terry.

This NBS book is very valuable to me, even after 60 years.

With close to 500 pages, it might help me to understand some HF-effects better.

 

One is in the waterfall (SSB 2.7kHz BW) where I see on a regular base a few periodic , vertical intensity minima and maxima.

Sometimes the lines are vertical, sometimes left or right shifted.

 

It is a multipath propagation ionospheric effect, I think.

All seems based on time varying amplitude and phase shifts

 

Any more detailed explanation?

Thanks

 

mit freundlichen Gruessen / Best Regards

 

Diethard E. A. Hansen

 

https://www.euro-emc-service.com  

 

Diethard Hansen | LinkedIn

 

Andy:  www.qrz.com/db/hb9cvq

 

 

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·      Deep inside "Measuring height of reflection at HF" - 1 Update

Deep inside "Measuring height of reflection at HF"

I4MFA W4MFA Eng. Marco Filippi <i4mfa...@gmail.com>: Aug 02 02:34AM -0700 Hi Terry, referring to > For details, check out this book > by one of my mentors, Ken Davies I noted above that imho chap. 4.3 (6 decades ago) has been nicely rewritten by Bob NM7M (3 decades ago) and - I agree - it is really interesting to understand the relationship between hmF2, foF2 and path (apart from any consideration related to O and X waves).   Il giorno sabato 2 agosto 2025 alle 03:04:19 UTC+2 terry....@noaa.gov ha scritto:   Gwyn,   Note that a radio wave in a plasma has a group path that is the the measured time of flight of a signal which is what a pulse or FMCW ionosonde would measure. But it also has a phase path, and they are not the same, especially in a magnetic plasma where the index of refraction is a tensor and the ray path is not the phase path.   Observed Doppler shift is the time derivative of the phase path from Tx to Rx.   For details, check out this book by one of my mentors, Ken Davies:   https://nvlpubs.nist.gov/nistpubs/Legacy/MONO/nbsmonograph80.pdf   It's complicated. Good Luck,   Terry W0ASP     On 7/27/25 03:02, 'Gwyn Griffiths' via HamSCI wrote:   Hello Marco Thank you for your interest in my article on this topic in RSGB RadCom August 2024. BY the way, the RSGB kindly allowed HamSCI to include the pdf in its repository at https://hamsci.org/publications/measuring-height-reflection-hf   Assuming a spherical Earth. Taking your example at 21 MHz on a 3000 km path with hmF2 at 300 km, using the equations on page 43 we get the following for a Doppler step of +0.1 Hz:   Initial path length = 3120.952 km Path velocity = -1.43 m/s Path length change over 120 seconds = -172 metres Path 120 seconds later = 3120.780 km Height 120 seconds later = 299.719 km   Therefore minimum dH observable under these conditions is 281 metres. Assuming also that all of the Doppler shift is attributable to the change in height.   73 Gwyn G3ZIL           On Friday, July 25, 2025 at 4:03:12 PM UTC+1 I4MFA W4MFA Eng. Marco Filippi wrote:   I found really interesting the work of Gwyn Griffiths, G3ZIL. I was wondering about the minimum dH we are able to measure in 120" using 0.1Hz doppler resolution on a 15M 3000Km path, assuming foF2 at 1500Km=8MHz - *obviously* - and hmF2=300Km. I believe there is quite a difference (20X) with a 80M/750Km test as the one reported, but I'm not sure my guess is correct. Answer are welcome!   -- Please follow the HamSCI Community Participation Guidelines at http://hamsci.org/hamsci-community-participation-guidelines. --- You received this message because you are subscribed to the Google Groups "HamSCI" group. To unsubscribe from this group and stop receiving emails from it, send an email to hamsci+un...@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/hamsci/d43c86bb-42bf-424f-80b7-96f1ca0b3b29n%40googlegroups.com <https://groups.google.com/d/msgid/hamsci/d43c86bb-42bf-424f-80b7-96f1ca0b3b29n%40googlegroups.com?utm_medium=email&utm_source=footer> .     -- Dr. Terry Bullett WØASP NOAA National Centers for Environmental Information (NOAA/NCEI) Cooperative Institute for Research in Environmental Sciences (CIRES) Terry....@noaa.gov 720-446-9775 (google voice) 978-337-9092 (cell) "Life is Complex. It has a Real part and an Imaginary part."

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[Bob WB0VGD]

Hi Diethard: 

Interesting comments!

Agree that NBS Monograph 80 is a great reference on the ionosphere...Ken Davies was a first rate writer and researcher. I first encountered his book during my high school years when my Dad placed the Dover edition of  Monograph 80 on my home desk. I started reading it and learned bits and pieces about the ionosphere and, as a result of my Dad's manipulation, I developed a deep interest in HF communications back then :-)

From your description of the patterns of the 2.7 kHz waterfall display, I think that you are seeing a combination of multipath and Doppler. For the past year , as a retired citizen scientist,  I have developed an experimental HF channel sounder using a combination of my ham transceiver and selected remote SDRs. This system has a 3 kHz bandwidth and uses PN sequences to measure the time-varying impulse response of an HF channel. While my system and associated signal processing does not provide absolute time, as an ionosonde does, it measures relative timing between scattering events and my Matlab software provides a time-varying channel impulse matrix from which I can get other time-varying channel parameters (Bello Functions). One of the plots that my code generates is identical to your waterfall display--in my code I call this plot the channel transfer function. In the near future, I will be happy to share some plots that I have obtained from baseband HF channel simulators and some real over-the-air measurements the 60m ham band. The patterns can get quite complex if you have multiple paths and high Doppler :-)

HF Propagation is cool stuff!

Best Regards & 73

Bob Johnk, WB0VGD

NTIA/ITS (retired)

Arvada, Colorado USA

. 

[euro.emc.service]

Hi Bob

 

Long time, no hear!

Thank you very much for your interesting response/comments on my periodic, propagation varying HF-waterfall “Fine Structure”-Minima-Maxima lines leaning left/right or being vertical.

I am eagerly awaiting your simulation/test results.

 

PS: off topic

I am working on an “EMC/HAM” paper TEMPEST related.

I have experimentally demonstrated UHF/VHF Spurs (RX port emissions, fully ETSI compliant) from 3 different K3S Elecraft HF TRX in my station can be used, (over the air, up to ca. <300m), to “remotely” read out my VFO QRG + Mode settings on HF .

There is a clear/complex correlation between HF (160 to 10m) VFO settings and Synthesizer generated Spurs. Motivation: On my QRZ.com und nearby 5. Ugly...D-QRM case here..

Stuff normally irrelevant for HAMs , but maybe interesting for other users.

 

Best Regards & 73 de HB9CVQ DK2VQ AK4IG

Diethard (Andy) Hansen

https://www.qrz.com/db/hb9cvq

https://www.euro-emc-service.com

 

 

 

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·      Digest for ham...@googlegroups.com - 1 update in 1 topic - 1 Update

Digest for ham...@googlegroups.com - 1 update in 1 topic

Bob WB0VGD <robert...@gmail.com>: Aug 04 07:25PM -0700

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[Andrew Rodland]

Yes, that sounds like frequency-selective fading caused by multipath (and when you see the "barber pole" effect of the stripes shifting in frequency with time, it means that at least one of the paths is experiencing Doppler). It's a big part of the sound of long-distance shortwave, and it's also a major factor in the design of OFDM modems, because it can cause one or more of the carriers to be wiped out completely for some period of time (and maybe a different one a moment later).