28Mhz short distance signal enhancments (100 miles) ?

Discussion in 'Radio Propagation Questions' started by G0FTD, Oct 14, 2017.

  1. G0FTD

    G0FTD New Member

    Dear All,

    There is a group of us that have regular transmissions on the 28Mhz band, typically over a distance of around 70-100 miles
    apart here in south east England.

    It is observed at random that we experience times of signal enhancement, at random, sometime for an hour, sometimes for a day
    and then it might go back to normal for a week.

    We can't find to rhyme or reason to this, either by time, solar events or high solar indices etc.

    It's like we are working an enhanced ground wave situation that just seems to come and go.

    Tonight it seems to be in excess, and my theory that we maybe working via some scatter mode (E or F layer) no longer fits,
    since we have both a high A and K index.

    Yet the short range signal enhancements on signal about 100 miles away is very good tonight.

    Anyone got any ideas as to what this mode could be ?

    73 de Andy
  2. Hi Andy,

    That is interesting and pleased to hear of 10m being used for local nets, hope its CW :))

    As a matter of observation over the last few years of Es data, the original notion that a Kp index of 3 or more is a big no-no for Es is not strictly true. A few reasons, but one main factor being that the planetary Kp may be very different to the regional K at your longitude. So far better to relate to say the value from Chilton, Fairford or Dourbes (when available). Another thing I've noticed is that if Es is pre-existing when the K goes up, it may take a while to quash the Es, so you may find Es concurrent with higher K indices. The off-vertical MUF benefit from being at some distance away from ground wave range is important, so it would be interesting to know the ranges/powers/antennas of the group.

    The daily plot of near real-time foF2 and MUFs at different skip distances is usually available on www.convectiveweather.co.uk/ionosphere soon to be replaced by www.propquest.co.uk

    Currently there are problems with the ionosonde data feeds for both Fairford and Chilton, but I hope to be able to use Dourbes soon. I have looked at Dourbes for last Saturday evening and attached the image below. You will notice there was an Es layer at the time, but not sure if that would have been enough, maybe others can comment.

    73 de Jim
    Screen Shot 2017-10-16 at 11.30.40.png
  3. G0FTD

    G0FTD New Member

    Hi JIm,

    Thanks for the enchanced info regarding sporadic E, and yes it's 99.9% CW for me these days ;-)

    I took a closer look at the paths in question, and they are only about 75 miles.

    This seems quite a short path length of Sp E, but a bit long for ground wave, so do you think the enhancement is due to Sp E or a backscatter mode ?

    I might have some interesting info for you for 28Mhz monitoring which I could give you off list.

    73 de Andy G0FTD
  4. G0FTD

    G0FTD New Member

    PS..forgot to mention about the ionosonde data website.

    It has to be the epitome of clarity for such info - well done.

    I don't think I've ever eseen anything so easy to use and read - ever. Please don't ever change for the format ;-

    73 de Andy

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