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Message-ID: <301460.22362.qm@web86506.mail.ird.yahoo.com>
Date: Fri, 29 Jan 2010 10:57:33 +0000 (GMT)
From: ALAN MELIA <alan.melia@btinternet.com>
To: rsgb_lf_group@blacksheep.org
In-Reply-To: <20100129092211.3507031E702@smtps01.kuleuven.be>
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Subject: Re: LF: Question to the groundwave
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Hi Stephan and Rik, yes Rik I was meaning to mention the late Reg's progra=
m. Your estimate is probably right and the thing is complicated further by=
 even in daytime the skywave being stronger than the ground wave beyond 10=
00km (see my plots of Brian CT1DRP's data on DCF39 to Oporto route) On the=
 longer paths you cannot rely on the skywave only consisting of one hop(wh=
ereas I believe this may be true at short distances) there is some evidenc=
e that at night on 500kHz there are two different paths even at quite shor=
t distances (cf the reported very deep fading on stations that cannot be=
 heard in daytime....i.e the fading is probably between two skywave path=
 rather than ground and skywave. Some of Graham's work suggests thes may=
 be reflection from two different heights on 500kHz rather than two hop...=
..not a phenomena that exists on 136kHz)

Great Fun.....much better than boring HF :-))

Alan G3NYK

--- On Fri, 29/1/10, Rik Strobbe <rik.strobbe@fys.kuleuven.be> wrote:

> From: Rik Strobbe <rik.strobbe@fys.kuleuven.be>
> Subject: Re: LF: Question to the groundwave
> To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
> Date: Friday, 29 January, 2010, 9:22
>=20
> =20
> Hello Stefan,
>=20
>=20
> ground waves (surfaces waves) are a tricky thing.
>=20
> The assumption you made (+6dB TX power =3D double distance)
> takes only the
> 2D spreading loss into account. This would be correct if
> the ground would
> be a perfect conductor and if the earth would be flat.
>=20
> In reality you have 2 additional losses: diffraction loss
> (due to the
> earth curve) and ground loss.
>=20
> The bad message is that these losses both have a more or
> less 1D
> behavior, and thus their attenuation is more or less linear
> to the
> distance.
>=20
> The late G4FGQ wrote a very good DOS application (named
> GRNDWAVE3) where
> you can put in a lot of parameters (distance, antenna
> efficiency,
> frequency, ground type, TX power) and it gives you the path
> attenuation,
> field strength at RX end and RX antenna voltage.=20
>=20
> It must be on the web on several places (google it), but in
> case you
> cannot find it I can send it to you.
>=20
> Just as an example the path loss this programme  gives
> for 137kHz
> and an average ground:
>=20
> 250km =3D 55.1dB
>=20
> 500km =3D 65.3dB
>=20
> 750km =3D 74.7dB
>=20
> 1000km =3D 83.5dB
>=20
> 2000km =3D 115.4dB
>=20
> 3000km =3D 144.5dB
>=20
> 4000km =3D 172.2dB
>=20
> 5000km =3D 199.0dB
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> As you can see doubling the distance "costs" far
> more that 6dB
> (by surface wave, sky wave is a different story).
>=20
> I haven't kept any records by I think that the surface
> wave limit for
> most amateur stations is 1000-1200km (on 137kHz), maybe a
> bit more in
> QRSS. Beyond that you are far better of with sky waves.
>=20
>=20
> 73, Rik  ON7YD - OR7T
>=20
>=20
> At 02:51 29/01/2010, you wrote:
>=20
> Hi Alan and LF,
>=20
>=20
> =20
>=20
> I know there are some of you who can easily
> answer my
> question that follows :-)
>=20
> =20
>=20
> The maximum distance of the groundwave at a
> specific
> fieldstrength E is (about) linear increasing with the
> antenna current of
> the TX antenna, right?
>=20
> So, if i have an antenna current of 0,5A and get a maximum
> distance of
> 1000km, i would reach 2000km with 1A (same RX, same
> surrounding noise
> level, same average ground properties, same OP ;-)
> )?.
>=20
> =20
>=20
> I expect, that the groundwave does not
> immediately stop
> beyond this 2000km border but rather decreases with 1/r,
> just as
> before.
>=20
> =20
>=20
> So, if we assume one is increasing the antenna current in
> the above
> example to 7A, is then a distance of 14000km possible?
> Sure, thats a very
> theoretical question since there will not be the same
> ground conductivity
> on the whole distance but anyway.
>=20
> =20
>=20
> And it is said that the groundwave is (nearly) not affected
> by the
> daytime, by the season and so on. There must be
> interferences with the
> sky wave, so QSB, but this does not affect the groundwave
> at an other RX
> QTH, where no sky wave is present!?
>=20
> =20
>=20
> If there is so much sea water between a transatlantic
> distance, why is it
> so difficult to do it with the groundwave? On HF or MF it
> is clear but on
> LF?=20
>=20
> =20
>=20
> Tnx for enlightning answers...
>=20
> =20
>=20
> Stefan/DK7FC
>=20
> =20
>=20
>=20
> Von:
> owner-rsgb_lf_group@blacksheep.org
> im Auftrag von ALAN MELIA
>=20
> Gesendet: Fr 29.01.2010 01:51
>=20
> An: rsgb_lf_group@blacksheep.org
>=20
> Betreff: Re: LF: Ok its a sea path .. but this is
> getting
> silly
>=20
>=20
>=20
> Ah this 500k stuff is too easy Graham :-))
> oh for 73kHz
> again !
>=20
>=20
> Alan G3NYK
>=20
> =20
>=20
>=20