Hello Alan,
I agree that the typical 500kHz QSB is indeed ionospheric multipath
causing interference. I surface wave was involved I would only notice
it with stations I can also hear during daytime.
About Reg's program: any idea what formula's are behind it ?
73, Rik ON7YD
PS: including some carriage returns in your mails would be nice ;-)
At 11:57 29/01/2010, you wrote:
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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