Re: LF: Question to the groundwave

[Rik Strobbe <rik.strobbe@fys.kuleuven.be>]

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
 

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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