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Message-ID: <194520.42398.qm@web86503.mail.ird.yahoo.com>
Date: Sun, 10 Jan 2010 23:11:59 +0000 (GMT)
From: ALAN MELIA <alan.melia@btinternet.com>
To: rsgb_lf_group@blacksheep.org
In-Reply-To: <20100110225447.qai3f5xv0gwkkocw@webmail6.kuleuven.be>
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Subject: Re: LF: Link budget calculation or estimation of dist for given power  on WSPR
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Hi Rik, Jim thanks for the plug...This estimate was tested against real re=
sults 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 fr=
om Jack Belrose VE2CV a long time professional LF expert in this area and=
 the methods employed are somewhat similar but the calculations are somewh=
at 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, sea=
son 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 onl=
y 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 nor=
mal coverage area. They are not intended to give an accurate measure of re=
ceived 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 groun=
d parameters at mid range. There could be quite big differences due to gro=
und parameters at bothe the transmit and receive sites. There can be a "fo=
cussing" effect at receive stations which are on or very close to the coas=
t. Then again is the ground is poor by the transmitter the low angle signa=
l will be attenuated so you will be dependent on high angle radiation whic=
h 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 transmis=
sion 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 month=
s 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.  =20

So keep plugging, the collection of reliable data is what Experimental Lic=
ences are for !! remember this is NOT an amateur band and some seem to thi=
nk!

Best wishes
Alan G3NYK



--- On Sun, 10/1/10, Rik Strobbe <Rik.Strobbe@fys.kuleuven.be> wrote:

> From: Rik Strobbe <Rik.Strobbe@fys.kuleuven.be>
> Subject: Re: LF: Link budget calculation or estimation of dist for given=
 power  on WSPR
> To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>, "Roge=
r Lapthorn" <rogerlapthorn@gmail.com>
> Date: Sunday, 10 January, 2010, 21:54
> Roger, Jim,
>=20
> On Alan's (G3NYK) website (http://www.alan.melia.btinternet.co.uk/simple=
.htm) I
> found:
>=20
> 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".
>=20
> Thus an extra hop would "cost" 13 to 18dB (+ free space
> loss ?)
>=20
> 73, Rik  ON7YD - OR7T
>=20
> Quoting Roger Lapthorn <rogerlapthorn@gmail.com>:
>=20
> > Do we know how many dB loss (over land and over sea)
> for a single hop Rik?
> >=20
> > 73s
> > Roger G3XBM