Hi Rik, Jim thanks for the plug...This estimate was tested against real results
but is sort-of +/- 10dB (or perhaps more :-)) ) I originally called it "silly"
but changed the name to "simple" after getting a big grin from Mike Underwood
at a Crawley LF Round Table a few years ago.... It is not dissimilar to the
techniques used in the ITU Recomendations. Bear in mind that was done for 136
and 500 maybe/is different!!
I cant find the paper at the moment but I have a very interesting paper from
Jack Belrose VE2CV a long time professional LF expert in this area and the
methods employed are somewhat similar but the calculations are somewhat more
sophisticated and include for instance, an ionospheric "focussing effect".
Basically calculate the free-space strength and then apply extra attenuation
for the ionospheric effects. These vary with time-of-day, season and state of
the Solar Cycle. Conditions are very good at the moment.
But also use Reg Edwards ground-wave calculator to check that the strength of
the ground wave is insignificant.
All the best calculations that the ITU spends a fortune collecting can only
estimate the level of QRM a transmitter is likely to give, for a certain
percentage of the year, to co-frequency stations which are out of its normal
coverage area. They are not intended to give an accurate measure of received
signal strength. The best you can do is to estimate the peak levels, but these
may be up to 6dB enhanced by constructive interference between two different
paths (say 1 hop plus 2 hop)
There should be no difference in the one hop signal depending on the ground
parameters at mid range. There could be quite big differences due to ground
parameters at bothe the transmit and receive sites. There can be a "focussing"
effect at receive stations which are on or very close to the coast. Then again
is the ground is poor by the transmitter the low angle signal will be
attenuated so you will be dependent on high angle radiation which is more
heavily absorbed that grazing/tangential signals (which give the longest hops)
In conclusion there is not an equation you can pump numbers into that will give
a realistic picture of the potential strength of the received signal an any
given distance. I remember being told that trans-Atlantic transmission was not
possible with only one watt ERP, when I started discussing it with the "two
Dave's" and Peter. The feeling it was possible was arrived at by monitoring CFH
in Halifax Nova Scotia every night for several months and estimating what 1W
ERP would do compared with 15 to 20kW ERP on the Canadian station. It did need
the "gain" of QRSS3 and a following wind......but it worked! That was before I
understood the effect of geomagnetic events properly.
So keep plugging, the collection of reliable data is what Experimental Licences
are for !! remember this is NOT an amateur band and some seem to think!
Best wishes
Alan G3NYK
--- On Sun, 10/1/10, Rik Strobbe <[email protected]> wrote:
> From: Rik Strobbe <[email protected]>
> Subject: Re: LF: Link budget calculation or estimation of dist for given
> power on WSPR
> To: "[email protected]" <[email protected]>, "Roger
> Lapthorn" <[email protected]>
> Date: Sunday, 10 January, 2010, 21:54
> Roger, Jim,
>
> On Alan's (G3NYK) website (http://www.alan.melia.btinternet.co.uk/simple.htm)
> I
> found:
>
> Allow for an extra "hop loss" of 12dB for every ionospheric
> "reflection" and 6dB for a land "bounce", say about 1dB for
> a sea "bounce".
>
> Thus an extra hop would "cost" 13 to 18dB (+ free space
> loss ?)
>
> 73, Rik ON7YD - OR7T
>
> Quoting Roger Lapthorn <[email protected]>:
>
> > Do we know how many dB loss (over land and over sea)
> for a single hop Rik?
> >
> > 73s
> > Roger G3XBM
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