Poor propagation

[David G. McGaw]

The WWV signal level is way down from what I would consider normal on
all bands right now.  15 is present, 10 is weak, 20 and 25 are
non-existent (should be strong).  No geomagnetic storms or flares are
happening.  What is going on?

David N1HAC in NH

[Bruce Crandall]

I just checked on my system here in VA.  Nothing on 5, a little surprising.  10 and 15 are about S9.  20 is S3 w/low noise - readable.  Nothing on 25.  I'm using OCFs for 80-10M and 60/30/15M.

Bruce

KN4GDX

FM18cs

Broad Run, VA

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73

[R Diehl]

Using a Hustler 6BTV ground mounted here WWV  on 5mhz I have no reception, 10 is maybe S2, 15 is S9 and 20 is S3

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[Bill Mader]

No signal on 5 MHz in VA would certainly not be surprising.  Here in north central NM it is barely audible on 5 MHz and not surprising at this time of day.

10 MHz is S8--typical for time of day.

15 MHz is about S3, not surprising for the distance and time of day.

Keep in mind, comparing S-units is a waste of time.  With few exceptions (Collins and Elecraft), there is no generic standard.  S9 on my K4 is -73 dBm.  Yours could be very different.  Additionally, S-units vary markedly.  The "standard" was 6 dB per unit but it varies widely now.  If we all measured in dBm, and used the same antennas, readings such as those might me something.

Do a VOACAP prediction to set expectations on most, not all, days.

73, Bill Mader, K8TE

ARRL New Mexico Section Manager

ARRL - The national association for Amateur Radio™

W6H NM Coordinator, Route 66 On-the-Air 5-14 Sep 2025

Duke City Hamfest BoD www.dukecityhamfest.org 19-21 Sep 2025

New Mexico QSO Party 11 Apr 2026

Secretary/Treasurer and Past President, Albuquerque DX Association 

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[Dave Lewis]

Re: WWW unusual propagation

Attached is a table of WWV signal strengths from 5 to 25 MHz recorded at 4 pm local time (20:00 UTC) here in South Florida, today and on two days about a year ago for comparison. The 20 MHz signal is maybe down a bit from last year, but otherwise all is very consistent -- which surprises me, given that I think we are beyond the peak of the solar cycle.

Bill, I agree with you completely on the futility of comparing uncalibrated S Unit measurements in general, but shouldn't signal strength comparisons using the same receiver and antenna (with identical receiver sensitivity settings) be credible?

73, 

Dave, W2HMT 

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[David Eckhardt]

Bill Madar:  The Icom radios are pretty good with calibration of the S-meter.  I've measured both my 7300 and 7610.  S-9 is -73 dBm and each S-unit below that is darn close to 3 dB less and less.  Above S-9, both are right on as well in 10 dB steps.  The Collins may hit -73 dBm at S-9 but even though they suggested the standard, below that, they do not hit 6 dB per S-Unit.  The worst I've ever measured, and that's probably 30 over the years, my Kenwood TS-2000X is the absolute worst.  Sadly, I never measured my K-2 which I no longer have.  Anan is also pretty good with the S-meter cal.  The older rige are all over the place and not worth comparing S-Meter reading.  They're just "R-Meters" for Relative Meters.

Dave - WØLEV   

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Dave - WØLEV

[bryan thompson]

Is this why I haven't received and digital contacts since last Friday im me here still learning

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[Carl Luetzelschwab]

All,

Just an FYI with respect to WWV reception and general propagation on our bands.

As we move into the summer months, the daytime F2 region MUFs (maximum usable frequencies) decrease. In other words, the electron densities go down. This is due to the change in composition of the atmosphere at F2 region altitudes. Here's an example of this trend on a path from my QTH to England for three levels of solar activity. Right now Cycle 25 is just a bit above the orange curve.

The higher MUFs will return in the fall and winter months. During the summer on 15m, 12m, 10m and 6m, the only thing many of us can do is hope for sporadic-E.

Carl K9LA

On Wed, May 7, 2025 at 2:16 PM David G. McGaw <david....@dartmouth.edu> wrote:

[Lawrence Naif]

Hi Carl,

What changes in the composition of the atmosphere lead to lower electron density in the summer months? Is it driven by low photoionization or higher recombination of free electrons with oxygen and nitrogen atoms and molecules? 

Also, how can I have a setup to measure this ? Any leads on his 

Thanks, 

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[Phil Erickson]

Hello Larry,

  The pattern Carl shows comes from basic ionospheric and atmospheric physics, in the competition between ionization (driven by solar EUV photons) and recombination (driven by chemistry).  In the F region, which is relevant for this discussion, the plasma is composed of O+ and electrons.  The O+ and electron source comes from ionizing neutral oxygen.  On the other side, the primary pathway for recombining electrons (e.g. sink) is with molecular nitrogen.  Since Earth's atmosphere is only weakly ionized (at most 100x less electrons and ions compared to neutrals), the neutral atmospheric composition dominates this basic picture.

  So the O/N2 ratio in the neutral atmosphere is critical to gauge the relative source of electrons: the numerator generates electrons while the denominator takes them away.

  In summer and winter, there is circulation in the neutral atmosphere between northern and southern hemispheres.  The circulation moves O-rich gas horizontally from the summer to the winter hemisphere, and enhances the source available for ionization.  (It is warmer in summer than in winter so the gradient flows towards the cooler part.).  So winter wins and summer loses.  Compare with Carl's graph.

  There are many many complications beyond this very simple level - winds, etc etc. - but this is enough for the discussion now.

Also, how can I have a setup to measure this ? Any leads on his 

  Carl's graph is not a measurement but is a prediction taken from the VOACAP model (nice front end available at https://www.voacap.com ).  That is a propagation model constructed from huge amounts of data on empirical reports of propagation of HF signals from the Voice of America service.  It was created to help their engineers determine how their broadcasts were getting out to various areas.

  Systems that measure electron density would use an ionosonde or an ionospheric radar.  Those are active transmitting systems and $$$ - at least for now.  (You also have the problem that an ionosonde needs to sweep over most of the HF band, and amateur radio can only transmit in narrow windows.). W2NAF's database of PSKReporter and other spots, extending over years, is a data-based way to see these seasonal patterns, and that's part of the funded science work he is leading.

73

Phil W1PJE

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Phil Erickson
phil.e...@gmail.com

[Carl Luetzelschwab]

Lawrence,

First, a big thanks to Phil for jumping in on this.

A typical O/N2 value between 250-300 km for winter is around 6. For summer, it is around 2. This comes from The High-Latitude Ionosphere and Its Effects on Radio Propagation, Hunsucker and Hargreaves, Cambridge University Press 2003, page 43. I've seen papers measuring this ratio, but darned if I know where they are in my pile of stuff at the moment.

Here's a plot of WSPR plots per day on 10-meters by Jim KG6TW in Georgia (ex-KX4TD) for a one year period. It tends to confirm this pattern.

Carl K9LA

[Phil Erickson]

Hi Carl,

  I'll help out - this is from Phil Richards' 2001 paper, pretty highly cited (https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2000JA000365):

  In that stacked figure, look at the 2nd row - ignore the dashed line (O/N2 ratio at 300 km), and just concentrate on the solid line (O/N2 at the F2 peak).  The seasonal pattern is clear.  Notice by the way there is a solar cycle variation too - as we get closer to solar maximum (like now), the change between summer and winter intensifies.  For reference, Solar Cycle 21 peaked in December 1979 - of course, we're at the top of Solar Cycle 25 now.

73

Phil W1PJE

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[Lester Veenstra]

“With few exceptions (Collins and Elecraft),”  and FLEX who go to sign cant effort to build configuration specific tables to keep the readout accurate.

B.T.W. A.T.T.  WWV 25 Mhz is  above noise floor, but not up to it’s usual.

 

Lester B Veenstra  K1YCM  MØYCM  W8YCM   6Y6Y W8YCM/6Y 6Y8LV (Reformed USNSG CTM1)

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[Lawrence Naif]

Thanks Phil- it seems like knowing the distribution of the O/N2 ratio in the F2 layer is a critical driver of ionospheric disturbance and hence TEC density/distribution.   The distortion in this ratio is smooth, or is it a sudden jump ?    any linkage to extreme weather events and this ratio?

 Best Regards,

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[Lawrence Naif]

Thanks, Carl- I am looking at the COSMIC 1 & 2 COSMIC  data - they have the Level 2 Atmospheric profiles without moisture ( atmPrf format), and the Atmospheric profile with moisture, might find them in this data set.

Is the graph referring to sunspots?

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[Lawrence Naif]

I got this developed some time back, pretty close to where we are now.  Suncycle 26 looks a bit risky..

Best Regards,

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[Phil Erickson]

Hi Larry,

  No, "spots" here refers to the number of times someone spotted or heard KX4TD's transmissions somewhere.  Nothing to do with sunspots - it shows you that paths were open.  The time-dependent behavior of the plot (more spots/paths open in winter than summer) is identical to the O/N2 behavior I reported, because it is mirroring the fact that more electrons are around (which refract the signal and enable a TX to RX path) in winter.

73

Phil W1PJE

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[Phil Erickson]

Hi Larry,

  O/N2 ratio is not really directly measurable using radio techniques because it occurs in the neutral atmosphere which isn't charged and therefore doesn't interact directly with EM waves.  People measure this ratio instead using other techniques, specifically ultraviolet emissions measured in space from instruments such as NASA's geosynchronous GOLD satellite (Global Observations of the Limb and Disk):

https://gold.cs.ucf.edu

  "Global-scale Observations of the Limb and Disk, or GOLD, is a NASA mission of opportunity that measures densities and temperatures in Earth’s thermosphere and ionosphere. GOLD makes these measurements, in unprecedented detail, with an ultraviolet (UV) imaging spectrograph on a geostationary satellite."

  The community is still trying to figure out all the dynamics of O/N2 variations over background conditions during things like geomagnetic storms.  Although the storms affect the ionosphere (charged portion), they also heat the neutral atmosphere through ion drift - neutral wind interactions and that can cause O upwelling which alters the O/N2 ratio and hence electron density production rate.  GOLD is designed to observe O/N2 changes (although only on the dayside since it is geosynchronous / fixed).  It is part of the quite complicated space weather picture of how the ionospheric electron density reacts to dynamic conditions.

73

Phil W1PJE

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[Bill Mader]

Yes, Dave, W2HMT.  Comparisons using the same radio are useful, but I would assert one needs to understand their limitations.  As Dave, W0LEV, points out, we need to measure what absolute levels (in dBm) each S-Unit is to provide more useful comparisons.  While Icom rigs usually have 3 dB per unit, others vary a lot from that with the "standard" supposedly 6 dB per unit.

A corollary is using PSK Reporter data derived from WSJT-X readings.  Those "SN"(should be (Signal+Noise)/Noise ratio) numbers can vary over time using the same radio at the same location.  Is the antenna the same as last measured?  Is the noise level the same?  Was the attenuator or pre-amp enabled?  This exercise points out how valuable "standards" are when there are so many.  Not all of us can provide accurate absolute measurements over time.

73, Bill Mader, K8TE

[Phil Erickson]

Hi all,

  I was led to believe that an increase of 1 S unit should be defined (all other things being equal as mentioned - e.g. noise level, multipath reflections, transmitter power, receiver impedance, etc. etc.) as a 2X increase in the voltage of the signal at the receiver terminal.  Again assuming the antenna is stable and not changing physical configuration, then that means the electric field in the incoming EM wave is also going up by 2X.

  Since power is proportional to E^2 with all those other factors stable then power would go up by 4X = 6 dB; hence the standard of 1 S unit = 6 dB.  This makes physics sense.

  Before the August 2007 continental US eclipse, I calibrated a consumer shortwave receiver (Panasonic RF-4900) with an external generator to set up a family member for simple WWV observations as the shadow passed by.  It was pretty hopeless with only 2 dB or so between S meter steps in midrange.  The manufacturers seemed to want the needle to swing maximally as signals varied ("look, it's doing something") and so it was horribly compressed on both the high and low ends.

73

Phil W1PJE

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[Phil Erickson]

Corrections: August 2017 eclipse, and never mind the transmitter power statement.  Not enough coffee.

73

Phil W1PJE

[Jim Willis]

Very interesting and information discussion, especially Dr Erickson's discussion on the ratio of 0/N2. As for the effect on propagation as measured by WSPR Spots, here is a plot of WSPR Spots per month of 2024 for my WSPR transmitter.

73,

Jim KG6TW

[Jim Willis]

Here is a plot of the 10-meter daily spot count after applying an 8-point moving average:

[Gedas V]

Hello group. I tried posting this just after the eclipse last year but not sure if it ever made it. If it will help anyone, I made some VLF/LF observations and measurements before/during and after the eclipse. The vertical dB scale is accurate however the absolute levels are not calibrated to any standard other than ADU.  I found it fascinating to see that some stations became stronger, some weaker. 73 Gedas, W8BYA EN70 Near Ft. Wayne IN

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[Lawrence Naif]

Thanks, Phil,

Are you looking at the GOLD data for the ratio to figure out all the dynamics of O/N2 variations under various assumptions?  

If the GOLD provides a good time series of  O/N2 observations, then it is possible to calibrate a proposed model.  

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