Spike wrote:
On 12/03/15 13:28, Brian Reay wrote:
Spike wrote:
On 06/03/15 23:02, Spike wrote:

Imagine a short rod vertical aerial not connected to ground, for the
(say) 160/80/60/40m bands, as might be found in a typical /M set-up, fed
with RF energy and operating over ground of average conductivity.

Many thanks to all who took the trouble to reply, with input ranging from
from the uncouth through the unhelpful to the deeply technical. The
modelling results and the graphs of the surface-wave propagation that
were provided will likely prove very useful for another propagation
project currently under study here.

One fact that has become apparent is that ground conductivity maps that
assign a value to region-wide areas are not to be trusted - there are
sometimes quite severe changes in local conductivity, and these could
encompass the ground that affects the radiation pattern from one's
antenna. However, models have now become sophisticated enough to
incorporate these into their predictions; the difficulty lies in
obtaining reliable conductivity figures for one's location, especially
those of poor conductivity where earth currents can run deep in the soil.
Although this isn't strictly an 'antenna' issue, it is nevertheless
fundamental to LF/MF/HF operation and highly pertinent as to how the
antenna contributes to the station performance.

While your local earth conductivity may well vary from that for you region,
in the scheme of things, especially if the path in question includes a
transit of sea water, to suggest it will play a significant role is
somewhat bold. To see this, look at the relative numbers I gave earlier for
North America.

If you understand what I wrote above, you'll see my point was about local
conductivity and how it affects the radiation pattern after being
launched from an antenna, rather than the variability along a signal
path, although I did mention for completeness that models can now take
such variability into account.

Local conditions will, of course, impact antenna efficiency.

The antenna efficiency is affected by its mechanical form. Earth losses
are something else, which can be factored in to estimate antenna system
efficiency, which, of course, isn't the same thing.

I suggest you do some more thinking before you challenge the work of
eminent people who have studied this area and published papers etc.

I asked a simple and straightforward question, which has been answered
only in part and not at all by you, in what appears to be your normal
spirit of offering every assistance short of actual help. As you mention
published papers, perhaps you'd let us know how many of yours have seen
the light of day in peer-reviewed prestige journals?

I find it difficult to accept input on this and similar matters from
someone who not only avoided taking out an HF licence for 30 years but
who also judges the finer points of HF receiver performance by noting
which DXpeditions might be subsidised by which manufacturer.


You are Gareth Alun Evans G4SDW AICMFP!

--
STC // M0TEY // twitter.com/ukradioamateur

On 07/03/15 01:31, Jerry Stuckle wrote:

And BTW - don't worry about the trolls who have no idea what they are
talking about - but insist on showing their ignorance, anyway.

Your advice was noted at the time, Jerry, but thanks anyway.

Despite it, the trolls have now posted here; one didn't take out an HF
licence until the new code-less scheme passable by 5-year-olds became
available, and the other one had to ask advice, after being licensed at
the UK's top level, on which sideband to use.

Their contributions to this thread suggest the topics are way above both
of them, and I note the regulars here are also avoiding replying to them.

--
Spike

"Hard cases, it has frequently been observed, are apt to introduce bad
law". Judge Rolfe

Spike wrote:
On 07/03/15 01:31, Jerry Stuckle wrote:

And BTW - don't worry about the trolls who have no idea what they are
talking about - but insist on showing their ignorance, anyway.

Your advice was noted at the time, Jerry, but thanks anyway.

Despite it, the trolls have now posted here; one didn't take out an HF
licence until the new code-less scheme passable by 5-year-olds became
available, and the other one had to ask advice, after being licensed at
the UK's top level, on which sideband to use.

Ah, still pushing that long-disproven lie, OM? A sign of desperation, it
seems. You do flail around so when you've shown yourself up.

--
STC // M0TEY // twitter.com/ukradioamateur