[Lf] propagation: CFH visible all day]

[Andre' Kesteloot]

Dave Sergeant wrote:

> >From Dave G3YMC
>
> Alan Melia wrote:
> >Hi all, I was somewhat surprised to hear several stations testing and
> >calling CQ within +/- 60Hz of 137.000kHz. I am not complaining as this makes
> >no difference to any monitoring I do (there are enough gaps for me to see
> >what is going on) but as CFH has been 6-8dB above the noise all day from
> >about 1130z to about 1700z today it seems like a good way of throwing away
> >an S-point, because CFH must be roughly the same strength all over Europe.
>
> I have not got involved with this thread until now, but there are a few things I would
> like to comment on in Alan's recent posting.
>
> 1.  I was listening yesterday here with Steve GW4ALG who was visiting, and we can confirm
> that CFH was quite copyable by ear around 1100z.  I notice it is also surprisingly strong
> this morning (0930z) peaking as high as s6.  I also heard one or two stations testing, and
> would comment on an increasingly common practice of not identifying when doing such
> testing.  Surely there is no harm in a quick callsign?  As to whether they would have lost
> QSOs because of CFH QRM that is debatable, and it is probably the case that the CQers were
> more interested in local G contacts than any sort of EU DX, which CFH would not have
> interfered with.
>
> 2.  It is important to realise that the reason we don't hear long distance stations on LF
> in the daytime is because of D layer absorption rather than anything to do with the F
> layer.  Hence any increase in CFH in daylight is as a result of a reduction in this D
> layer absorption - in the winter when the sun is weak it is common (at least on 160) to
> hear stations at considerable distance in the daytime.  With a station of the power of CFH
> it is reasonable to assume that there is still some residual signal even after the D layer
> path loss is included, and although some enhancement in the F layer would also increase
> signal levels it is the D layer which is the prime variable. It may be that the effects of
> solar storms reduce the daytime ionisation process in the D layer, or it may simply be
> normal seasonal variations.  Remember this is the first 'season' we have monitored CFH
> after their recent TX/antenna changes.  I suspect as autumn approaches CFH may well become
> more consistent in the daytime. Note also that until sunrise in VE (1000z?) at least some
> of the hops are not effected by D layer absorption and the total path loss will be less.
>
> 3.  Although it may be interesting to monitor CFH as an indication of long distance
> propogations, it would be an unreserved optimist to believe there is any hope of a
> transatlantic QSO on LF in these circumstances.  Last winter CFH was peaking 20 over s9 at
> night, and we may find it even stronger this year.  Perhaps the November tests will give
> us a feel as to how much margin we have, but realistically any reception of CFH in the
> daytime is of academic interest only.
>
> 73s Dave
> sergeantd at compuserve.com
> dsergeant at iee.org
> http://ourworld.compuserve.com/homepages/sergeantd