From: "kate moore" <mek@leicester.ac.uk>
To: "lfgroup" <rsgb_lf_group@blacksheep.org>
Subject: LF: Observations
Date: Wed, 16 Feb 2000 09:10:31 -0000
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Congratulations to Larry, Bob and the others for the interesting
observations of European signals over the weekend. From the amateur signals
I heard and worked, conditions were much enhanced, coinciding with a very
high A-index. What would be particularly useful now would be to continue
carefully  monitoring these signals, using the experience gained, so a
picture of 'average' trans-Atlantic propagation on these frequencies can
be built up, and usable peaks and enhancements predicted with some
confidence. Let's hope we still have a good few weeks before the increase
in static levels makes this work more difficult. Keep up the good work,
guys.

                          -------------------

Mike G3XDV wrote:
>A puzzle is that, although I am giving reports
>about one S-point down on G4GVC's legendary
>receive system, an exception is HB2ASB who was
>barely audible with me in an S4 noise level when
>John and G3YXM were giving him S6 or S7. This is
>the second time I have noticed this phenomenon. I
>have heard (and worked) Toni before at good
>strength.

and Steve GW4ALG wrote:
> I also found Toni's signal barely copyable Sunday morning when John and
> Dave were giving him good reports, something I have also experienced
> before.

This is what I alluded to briefly last week.
>From my own careful observations I have noticed quite large variations in
the strength of the more distant amateur signals on 136kHz. These
variations seem to change over quite small geagraphical distances. There
are times when I seem to be the only G station calling/working a DX station;
at other times I can hardly (or cannot) hear the station another G is
working. Obviously others are noticing the same effect, although it seems
partly dependant on the types of antennas in use at each end of the path.
It has also seemed particularly marked over the last few weeks, but this
might be complicated by the increase in activity and us becoming more
familiar with signals over the longer paths.

A few more examples:
- On Feb 5th I worked Toni HB2ASB at 08.12UT, giving him a 569 report. Not
much more than half an hour later, I heard G6RO calling Toni and (I think
it was) PA0SE working him, but could hear nothing whatsoever of Toni, and
suspect I had just been calling CQ on his frequency! (Sorry).
- Last Sunday (13th) at 11.12UT OZ8NJ replied to my CQ and I gave him a 569
report. Immediately afterwards Ray GI3PDN called me and commented that he
could not hear Niels, despite having worked him previously. Later in the
afternoon I heard I5MXX work OZ8NJ; Niels was then barely RST-339 here but
Marzio was an excellent signal.
- Dave G3YXM runs rather more power than me into a fairly traditional
top-loaded vertical which is around half as high again as my antenna. As
would be expected, Dave usually gets reports at least an S-point better than
I do. However, on two separate occasions recently (although not last Sunday)
I have found myself calling Toni at the same time, on exactly the same
frequency as Dave, when Toni has replied to me first.
This is particularly interesting: although my antenna is loosely configured
as an inverted-L, only about 4m of it is exactly vertical. The rest is
predominantly horizontal, sloping gently upwards to the far end. Although it
is reasonably long, it is made from a single very thin wire, so has quite
low capacitance to ground.
There is little doubt in my mind that with this antenna I am often able to
capitalize on the large amounts of skywave that seem to be present on many
amateur signals on 136kHz, and that this skywave causes marked differences
in signal strengths over quite small distances. We still have a lot to
learn on LF when it comes to (relatively) low power and small (in terms of
wavelength) antennas....... and of course that is exactly what AMATEUR radio
is all about.


         Regards  John G4GVC near Leicester, IO92JP

    **  TX: Synth + 400W RF from modified 'G3YXM' Mosfet PA           **
    **  RX: TS-850S with 3 x CW filters and 0.5ppm TCXO               **
    **  Ant: Inv-L 60m long, 6m high at feed end, 12m high at far end **


Kate Moore
mek@le.ac.uk

Department of Geography
University of Leicester
Leicester
LE1 7RH
UK
Tel: 0116 252 3855
http://www.geog.le.ac.uk/mek