Hi Stephan and Rik, yes Rik I was meaning to mention the late Reg's program.
Your estimate is probably right and the thing is complicated further by even in
daytime the skywave being stronger than the ground wave beyond 1000km (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(whereas I believe this
may be true at short distances) there is some evidence that at night on 500kHz
there are two different paths even at quite short 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 <[email protected]> wrote:
> From: Rik Strobbe <[email protected]>
> Subject: Re: LF: Question to the groundwave
> To: "[email protected]" <[email protected]>
> Date: Friday, 29 January, 2010, 9:22
>
>
> 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:
> [email protected]
> im Auftrag von ALAN MELIA
>
> Gesendet: Fr 29.01.2010 01:51
>
> An: [email protected]
>
> 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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