Welcome to the Radio Propagation Questions forum

Discussion in 'Radio Propagation Questions' started by Steve Nichols G0KYA, Nov 11, 2014.

  1. Steve Nichols G0KYA

    Steve Nichols G0KYA Administrator

    Hello and welcome to the new RSGB Propagation Questions forum.

    This has been set up to help RSGB members better understand radio propagation. It will be monitored by members of the Propagation Studies Committee, which specialises in everything from LF to light waves.

    So if you want to know why you were able to hear the Pacific on 40m, or why distant 2m repeaters suddenly appeared one morning, post your questions here and we'll try to answer them.

    You also have access to a lot of propagation resources on the RSGB web site.

    To start you off, we have a free downloadable e-book entitled "Understanding LF and HF Propagation". This is a collection of features that appeared in RadCom and take you through a month-by-month view of propagation themes.

    Steve Nichols G0KYA
    RSGB PSC Chairman
  2. Frank Johnson

    Frank Johnson New Member

    Thanks for the link to the E-Book.
    An excellent "read", highly recommended refresher.
    Frank, g0gsr
  3. G3YRZ

    G3YRZ Member

    Hi Steve, and thanks for opening a forum on this fascinating topic. As one of the many
    amateurs not professionally connected to radio/electronics, I keep my eye out for any
    sources of understandable information. Still learning, despite the age of my licence!

    I use indoor antennas, attic installation. A full size bent 80m dipole, and a 20m folded
    dipole using 300 ohm ribbon. Over the past few years I've worked into USA and Canada
    on 80m SSB, and overall 83 DXCC countries and 26 zones confirmed almost all on SSB at 100W.

    The 20m dipole works on 15 and 6 metres on the odd halfwave basis, and the 80m dipole also
    gets me QSOs on 30, 17, 12 and 10 metres on the same basis. No need for traps, very
    much a compromise, but people hear me!!

    My main band of interest is 20m, and I have done quite well being in the right place at
    the right time for DX. The thing that fascinates me though is the speed with which the
    band collapses after nightfall, something I notice acutely as I am working "on the edge"
    with an indoor antenna and the inherent field strength loss that implies. Is this a sudden
    change in layer height or composition? Connected to this, right now on 20m (1650 0n 20 11 14)
    the grey line/twilight boundary is right down through Africa, SFI=170, SN=72, A=8, K=1,
    MUF=26.6 for a 3000Km path. All I can hear is a solitary, and very loud, Italian. There may
    be other factors such as people actually being on 20 metres, but I see this scenario too
    often for it to be station population or an actual fadeout. I find that the band
    will now either die completely or will pick up later.

    Could you help with this?


  4. Steve Nichols G0KYA

    Steve Nichols G0KYA Administrator

    Hi John,

    Firstly, thank you your compliments about the forum – much appreciated.

    Now, about the Maximum Usable Frequency (MUF). The MUF tends to be higher in the winter than in the summer, mainly due to a change in the chemical make-up of the ionosphere. There is more atomic Nitrogen/Oxygen in the Winter and fewer molecular components. As it is easier to ionise atoms than molecules the overall ionisation levels can be higher in winter and the MUF can be higher, even though there is less solar input (the so-called winter anomaly).

    However, what we do find is that the bands close a lot quicker in the winter. In the summer 20m can be open throughout the night, but in the winter it can close in the early evening on some paths.

    This will also depend upon the path itself and other factors, such as the Solar Flux Index and the state of the ionosphere due to solar storms and coronal mass ejections.

    Paths to the east will close faster than paths to the west. But it is more complex than this, especially for paths that cross the equator. This is because it is mid winter here, but mid summer in the southern hemisphere.

    If you look at my monthly propagation maps at:


    You'll see that paths to South Africa on 20m actually IMPROVE after dark – and even be possible around midnight on 20m at this point in the solar cycle.

    Conversely, you will only be able to work South Africa on 10m during the day.

    The issue with 20m is that D layer absorption can be quite high near solar maximum so again, conditions may appear to be better towards and after sunset on some paths. Eg South Africa.

    If a picture is worth a thousand words, playing with VOACAP Online will show a lot of this.

    Throw in the fact that the ionosphere has to settle after sunset, with the D layer recombining, the E layer rapidly diminishing (but not disappearing completely) and the F1 and F2 layer combining to form a single F layer and you begin to see some of the factors at play.

    If you register you can see a lot of this in action via the Chilton Digisonde – see:


    We have also had a lot of geomagnetic disturbances recently due to CMEs and increased solar wind speeds. These have affected the ionosphere quite badly, so MUFs and Critical Frequencies (F0F2) have been a bit erratic.

    Also, it could be that a solar flare has affected the sunlit side of the earth at that point, making paths to the west at sunset difficult.

    I hope this helps.

    Regards, Steve G0KYA
    PSC Chairman
    Last edited: Nov 24, 2014
  5. M6RIK

    M6RIK New Member

    Propagation is one of the things which deeply interests me about radio communication. Far more so than building home brew equipment or rag chewing. I'm really pleased to see the RSGB pushing this kind topic.
  6. G3YRZ

    G3YRZ Member


    Thank you so much for setting out a lot of helpful detail.

    I have used Chilton for some time, and resort to Dourbes during Chilton's short and
    longer outages. But I have no experience of the graphic programs like VOACAP and
    your own propagation maps, which I have bookmarked.

    I have also used the map at http://solar.spacew.com/www/realtime.html
    for some time, and may have mislead myself. Basing things on 3000 km hops, I figured
    and discovered that when the 14 MHz countour on the MUF map reached Gibraltar or further
    south, I wouldn't hear much at all during the winter I reckoned that my first hop happened in
    that area and found nothing to help the next one. The exceptions were strong Caribbean
    stations like 9Y4D and some Brazilians. I reckoned that the many close contour lines around
    the Caribbean and northern South America at night had something to do with this. Your own
    propagation map sheds some extra light on this, many thanks. Not forgetting that the
    world is not flat!

    My money on the significant loss of signals at around 1600 to 1700Z is on the huge changes
    in the ionosphere around sunset when ions recombine and daytime states go to
    night-time states. Everything settles down later, either no signals at all or a recovery. How
    long do the D and E layers actually remain in place after nightfall especially when there
    has been significant solar activity?

    What I do know is that I can get out on my folded dipole in the attic, and every bit of
    technical information helps in one way or another, so thanks!

    And hello Richard M6RIK. It is magic that does it...


  7. M6RIK

    M6RIK New Member

    Hi John.
    It's a little more scientific than magic but i would agree that there is something quite magical about the way our signals go into the aether and land somewhere completely different where amazingly there is usually someone else with a TRX who can and is willing be communicated with!
  8. Steve Nichols G0KYA

    Steve Nichols G0KYA Administrator

    No Richard, it is magic ;-)

    Well John, with regards to the D and E layers it really depends upon the location, time of year and, as you say, state of the sun.

    This time of year the D layer seems to vanish quite quickly (at least in Northern climes) - you can tell this by listening to distant medium wave stations, which start to appear before sunset. We are also seeing long path openings to the west coast of the USA on 7MHz before sunset.

    I know that Carl K9LA has done a lot of work on the E layer. One theory is that it continues to exist at night due to galactic cosmic rays (GCRs). It certainly remains, even if it is weak. See http://k9la.us/. He also has two excellent free books for download that were written by the late Bob Brown NM7M. These are The Little Pistol’s Guide to HF Propagation and The Big Gun’s Guide to Low-Band Propagation. You might them them both helpful, along with Carl's features.

    Steve G0KYA
  9. MI0ZAO

    MI0ZAO New Member


    In your second post, there is the statement:

    " . . . even though there is more solar input (the so-called winter anomaly)."

    Should this read 'less' rather than 'more'?

  10. Steve Nichols G0KYA

    Steve Nichols G0KYA Administrator

    Hi Ross,

    Yes, you are right - I'll have to edit it. What I meant was despite there being more solar output impacting the northern hemisphere in the summer (due to the earth's tilt) overall MUFs are lower than in winter due to the ionosphere's different chemical make-up. In winter there are predominantly more nitrogen and oxygen atoms, rather than diatomic molecules, which are easier to ionise.
  11. M6RIK

    M6RIK New Member

    So when does it stop being magic and become science?

    Is it magic to someone with a 2x0 callsign? or do you have to have an M0 call before it stops being magic?
  12. MI0ZAO

    MI0ZAO New Member


    Its suprising how many texts (even those for professional HF users) ignore the winter anomaly and state that the MUF will be higher in summer than in winter.
  13. G3YRZ

    G3YRZ Member

    Thanks Steve. You are a mine of information and useful links, which will keep me quiet for some time!

    Richard - it was magic for me when I first made a crystal set and heard the medium wave was different
    at night, and explored the short wave band on my parents' domestic receiver. It is still magic now, despite
    my looking at the science as much as I can. What never ceases to amaze me is how I can get contacts
    when all the figures say it is impossible. The science is never dead accurate, which is why the
    propagation predictions are seldom if ever 100% certain. And how the waves get there on 160 in
    particular can be a mystery despite all the science.

    Yes, there is usually someone somewhere to talk to, a great thing about the hobby! Which is your favourite
    band? Mine is 20 metres, because that is the best antenna I can fit in.


  14. M6RIK

    M6RIK New Member

    10m is the band for me. decent antennas and favorable conditions at present make the band a joy.

    I made a crystal set when I was a youth too. luckily the school science department I went and asked for a diode was run by G3OTE Ron Binns. A few weeks later the crystal set was retired and a very capable multiband transistor reciever with an lm380 audio amplifier had been designed and constructed under his supervision. He was what our friends over the pond would call an elmer. I learnt a lot from him.
  15. James Hollander

    James Hollander New Member

    Does anyone have an explanation for the unusually good propagation last night on 630m and 2200m? Congratulations to all involved in last night's trans-atlantic (TA) WSPR activity! 73, Jim H W5EST Little Rock, AR USA

    On 630m, the action between New England and EU/UK was relatively clustered in time. Reception moved westward from Germany to France and then to England and Spain.

    In a 630m propagation event spanning one-half hour 0358-0428Z only, German stations DH5RAE and DJ0ABR derived all their WSPR decodes of WG2XKA and WG2XPJ. Both DH5RAE and DJ0ABR registered some peaking about 0410Z in WG2XKA SNRs. A total of 8 USA station decodes registered in Germany--3 at DH5RAE and 5 at DJ0ABR. Two-way pairing of decodes between WG2XKA and DH5RAE included 0414Z DH5RAE into WG2XKA, bracketed by 0410 and 0418 decodes of WG2XKA at DH5RAE.

    A little later at 0428 and 0436Z, a pair of WG2XKA decodes registered in France at F1AFJ.

    Still later at 0436-0518Z, G3XKR in southwest UK had four WG2XKA decodes with no obvious SNR peaking.

    0418-0526Z marked a more spread-out event set of 6 decodes of WG2XKA into Spain's EA1FAQ. These decodes lacked any obvious SNR peak too. The time-spreading suggests a North-South aspect to this 630m event as well.

    SFI: 122 A-index: 13 K-Index: 2 No unusual SFI departures have occurred, with SFI in a range 120-124 last four days April 1-4. http://www.spaceweather.ca/solarflux/sx-5-flux-eng.php

    Geomagnetic index and aurora don’t look unusual.http://www.hamqsl.com/solar3.html

    A full moon and a lunar eclipse occurred today April 4: start 0901z, to 1200z total, to 1459Z end. http://www.timeanddate.com/eclipse/total-lunar-eclipse.html

    2200m showed unusual activity last night including a trans-atlantic crossing from Germany to USA.

    LF:W1TAG hearing DK7FC 137.610 0030-0400z 6 spots -36 to -38dB.

    UA4WPF 137.616 2300, 2346z into EW6BN, G3XKR, RN3AGC, SM2DJK, SP5XSB, SV8RV-1, SV8RV-4, UA0SNV, UW8SM.

    160m had a good night last night. 160m has shown several good nights recently involving trans-Pacific and trans-Atlantic decodes.
  16. James Hollander

    James Hollander New Member

    The April 4 event was remarkable also because it allows some rough calculations. If a tidal atmospheric gravity wave (AGW) was responsible, I calculate its speed westward at ionospheric altitude high over the Atlantic Ocean along the great circle path from WG2XKA to DH5RAE at 9.75km/min, and its effective width 244km (151 miles). 73, Jim H W5EST.
    Separate solar and lunar tidal peaks of concentration in the ionosphere approximately coincide at new moon and full moon and even more nearly coincide around lunar eclipse and solar eclipse events as the tilted Earth turns. As I understand it, compression wave (deep subsonic) patterns emanate from these tidal peaks in the ionosphere.
    The speed component of the AGW wavefront along a 2-hop great circle would be one-quarter of the velocity of the reception midpoint from country to country. First I roughly set the midpoint times of reception April 4 in Germany DH5RAE & DJ0ABR E. Bavaria at 0415Z, France F1AFJ 0430Z, and Devon UK G3XKR 0500Z. Use a great circle distance calculator along one great circle from XKA to each of these stations. Then make a table:
    Path Distance (km) Difference (km) from Germany
    WG2XKA to DH5RAE 6180 0
    WG2XKA to F1AFJ 5434 756
    WG2XKA to G3XKR 4956 1224
    Averaging 756km/15min with 1224km/45min = (50+27)/2 = 39km/min or 650 m/sec.
    Estimated AGW speed along the XKA/DH5RAE great circle path for 2 hop propagation is ¼ of 39km/min and ¼ of 650m/sec, yielding a speed estimate of 9.75km/min or 162m/sec. This is plausible compared to the speed of sound in the ionosphere being roughly 100-250m/sec (from literature).*
    Estimated reflective stripe width of the AGW along the XKA/DH5RAE great circle path uses the estimated speed of 162m/sec. Average duration of decodes at DH5RAE and DJ0ABR is 25 minutes based on 20 and 30 minutes of respective decode durations. The Germany decode durations were also about midway between the 10 minute and 40 minute durations of reception in France and England respectively.
    Estimated AGW stripe width = 9.75km/min x 25min = 244km (151 miles).
    This estimated width is comparable to horizontal wavelengths 100-300 km for medium scale temporary ionospheric disturbances (MSTIDs). However, I would expect a far smaller reflective stripe width on the order of 1/10 wavelength from a MSTID because I presume that part of it would have to be nearly planar and horizontal to reflect effectively to the destinations. If this event results from a tidal cause, the effective stripe width may however be wider than that of a MSTID stripe.
    * Harris, T. J., M. A. Cervera, and D. H. Meehan (2012), SpICE: A program to study small-scale disturbances in the ionosphere, J. Geophys. Res., 117, A06321, doi:10.1029/2011JA017438.
  17. G3NYK

    G3NYK New Member

    Hi Jim, I suspect that the events of April 4th may not have been as unusual as you suggest. Yes there was a lot of activity which helps. The indexes you quote have little impact on LF propagation but look ar the Disturbance Storm Time index (Dst) this had climbed back from a low of about -240nT and some dire conditions, and by the the 4th was up to around -10nT and very stable. I take this to indicate that there is little charge in the ring current to precipitate into the ionosphere and periods when the Dst index is above -20nT are more likely to be good.

    The Dst is not a direct predictor of good conditions and there are other mechanisms which affect the received signal level. The Dst is better at predicting when contacts are not likely. I am intrigued that you think gravity waves could be one though I am at a loss to see how yet (I have yet to find a copy of your reference) I do have a fairly big data base of transatlantic path signal strengths I collected in the early 2000s I will dig it out and see whether I can find any interesting effects.

    Alan Melia G3NYK
  18. James Hollander

    James Hollander New Member

    Hi Alan,
    Yes, you're right, a few instances of same-night decodes from a USA station into Germany, Benelux, France, UK did occur in mid/late February and in mid-March on 630m. April 4 had decodes that time-transitioned from country to country in a way that permitted the speed estimate, but that night may not have been unique this year. Thanks for bringing up Dst too. For your convenience, the Harris et al. article is viewable at http://onlinelibrary.wiley.com/doi/10.1029/2011JA017438/epdf
    I look forward to more of your insights using the data you mentioned.
    73, Jim H W5EST

Share This Page