Date: Fri, 29 Jan 2010 10:22:18 +0100
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
From: Rik Strobbe <rik.strobbe@fys.kuleuven.be>
References: <473484.31039.qm@web86505.mail.ird.yahoo.com>
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Message-Id: <20100129092211.3507031E702@smtps01.kuleuven.be>
Subject: Re: LF: Question to the groundwave 
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Hello Stefan,

ground waves (surfaces waves) are a tricky thing.
The assumption you made (+6dB TX power = 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.
In reality you have 2 additional losses: diffraction loss (due to the 
earth curve) and ground loss.
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.
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.
It must be on the web on several places (google it), but in case you 
cannot find it I can send it to you.
Just as an example the path loss this programme  gives for 137kHz and 
an average ground:
250km = 55.1dB
500km = 65.3dB
750km = 74.7dB
1000km = 83.5dB
2000km = 115.4dB
3000km = 144.5dB
4000km = 172.2dB
5000km = 199.0dB
As you can see doubling the distance "costs" far more that 6dB (by 
surface wave, sky wave is a different story).
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.

73, Rik  ON7YD - OR7T

At 02:51 29/01/2010, you wrote:
>Hi Alan and LF,
>
>I know there are some of you who can easily answer my question that 
>follows :-)
>
>The maximum distance of the groundwave at a specific fieldstrength E 
>is (about) linear increasing with the antenna current of the TX antenna, right?
>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 ;-) )?.
>
>I expect, that the groundwave does not immediately stop beyond this 
>2000km border but rather decreases with 1/r, just as before.
>
>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.
>
>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!?
>
>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?
>
>Tnx for enlightning answers...
>
>Stefan/DK7FC
>
>
>----------
>Von: owner-rsgb_lf_group@blacksheep.org im Auftrag von ALAN MELIA
>Gesendet: Fr 29.01.2010 01:51
>An: rsgb_lf_group@blacksheep.org
>Betreff: Re: LF: Ok its a sea path .. but this is getting silly
>
>Ah this 500k stuff is too easy Graham :-)) oh for 73kHz again !
>
>Alan G3NYK

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<body>
Hello Stefan,<br><br>
ground waves (surfaces waves) are a tricky thing.<br>
The assumption you made (+6dB TX power = 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.<br>
In reality you have 2 additional losses: diffraction loss (due to the
earth curve) and ground loss.<br>
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.<br>
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. <br>
It must be on the web on several places (google it), but in case you
cannot find it I can send it to you.<br>
Just as an example the path loss this programme&nbsp; gives for 137kHz
and an average ground:<br>
250km = 55.1dB<br>
500km = 65.3dB<br>
750km = 74.7dB<br>
1000km = 83.5dB<br>
2000km = 115.4dB<br>
3000km = 144.5dB<br>
4000km = 172.2dB<br>
5000km = 199.0dB<br>
As you can see doubling the distance &quot;costs&quot; far more that 6dB
(by surface wave, sky wave is a different story).<br>
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.<br><br>
73, Rik&nbsp; ON7YD - OR7T<br><br>
At 02:51 29/01/2010, you wrote:<br>
<blockquote type=cite class=cite cite=""><font size=2>Hi Alan and LF,
<br>
</font>&nbsp;<br>
<font size=2>I know there are some of you who can easily answer my
question that follows :-)</font><br>
&nbsp;<br>
<font size=2>The maximum distance of the groundwave at a specific
fieldstrength E is (about) linear increasing with the antenna current of
the TX antenna, right?<br>
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 ;-) )?.</font><br>
&nbsp;<br>
<font size=2>I expect, that the groundwave does not immediately stop
beyond this 2000km border but rather decreases with 1/r, just as
before.<br>
</font>&nbsp;<br>
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.<br>
&nbsp;<br>
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!?<br>
&nbsp;<br>
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? <br>
&nbsp;<br>
Tnx for enlightning answers...<br>
&nbsp;<br>
Stefan/DK7FC<br>
&nbsp;<br>
<hr>
<font face="Tahoma" size=2><b>Von:</b> owner-rsgb_lf_group@blacksheep.org
im Auftrag von ALAN MELIA<br>
<b>Gesendet:</b> Fr 29.01.2010 01:51<br>
<b>An:</b> rsgb_lf_group@blacksheep.org<br>
<b>Betreff:</b> Re: LF: Ok its a sea path .. but this is getting
silly<br>
</font><br>
<font size=2>Ah this 500k stuff is too easy Graham :-)) oh for 73kHz
again !<br><br>
Alan G3NYK<br>
</font></blockquote></body>
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