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<DIV><FONT face=Arial size=2>Carlos,</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Nalguns países isso é um dado. Seria importante, ao
menos para treino e situações de emergência apenas.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Esperemos a ver ...</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>73, Mariano</FONT></DIV>
<DIV> </DIV>
<BLOCKQUOTE
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=radiofarol@gmail.com href="mailto:radiofarol@gmail.com">Carlos
Mourato</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=cluster@radio-amador.net
href="mailto:cluster@radio-amador.net">Resumo Noticioso Electrónico ARLA</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Monday, July 09, 2007 6:48 PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: ARLA/CLUSTER: Cover very
short distances on HF.(NVIS reports byTom(W6QJI)</DIV>
<DIV><BR></DIV>
<DIV>O ano passado apanhei NVIS a chegar aos 14Mhz!, mas foi menos de
uma semana. Depois estações a 100km em 20m "fugiram". Enquanto deu, cheguei a
escutar estações de Lisboa com 59+30!</DIV>
<DIV>...Precisamos da banda dos 5Mhz como os ingleses tem.</DIV>
<DIV> </DIV>
<DIV>73 de CT4RK<BR><BR> </DIV>
<DIV><SPAN class=gmail_quote>2007/7/9, Mariano Gonçalves <<A
href="mailto:ct1xi@sapo.pt">ct1xi@sapo.pt</A>>:</SPAN>
<BLOCKQUOTE class=gmail_quote
style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">João,<BR><BR>O
que o Tom diz: «rarely exceeds 6 MHz ...» isso depende da latitude
do<BR>lugar e do campo magnético terrestre (incluindo a cintura de Van
Allen). <BR><BR>Em África, recentemente, quando estive na EUFOR Kongo e
Gabão, por exemplo<BR>cheguei aos 12 MHz, e o típicos é 8 ou 9 MHz. Já aqui
na Península Ibérica,<BR>raramente excede os 5 ou 6 MHz, por acaso, este ano
chegou aos 8 MHz, muito <BR>excepcionalmente.<BR><BR>Se quiseres, tenho aqui
instalada uma antena NVIS da HARRIS, estou a fazer<BR>estudos nessa área,
para desenvolver novas antenas (de âmbito industrial
e<BR>militar).<BR><BR>73, Mariano<BR><BR><BR><BR>----- Original Message
-----<BR>From: "João Gonçalves Costa" <<A
href="mailto:joao.a.costa@ctt.pt">joao.a.costa@ctt.pt</A>><BR>To: <<A
href="mailto:cluster@radio-amador.net">cluster@radio-amador.net
</A>><BR>Sent: Monday, July 09, 2007 1:52 PM<BR>Subject: ARLA/CLUSTER:
Cover very short distances on HF.(NVIS reports
by<BR>Tom(W6QJI)<BR><BR><BR>Hi,<BR><BR>I've read discussion in this session
about the inability to cover very short <BR>distances on HF. There just has
to be something wrong or overlooked. The<BR>two things that come to mind are
a sick rig, or bad coax, at one end or<BR>excessively high NVIS Critical
Frequency (f0F2).<BR><BR>F0F2 can be seen at Near-real-time F2 Layer
Critical Frequency on the <BR>Internet. F0F2 --- the<BR>highest frequency at
which NVIS propagation is supported by the ionosphere -<BR>rarely exceeds 6
MHz, in the northern hemisphere, at this point in the solar<BR>cycle, this
time of year and the time of day. And, it does vary considerably <BR>from
day to day. The global curve set is updated every five minutes While<BR>the
curves shown on the site are not brick walls, 40 meter NVIS, with f0F2<BR>at
6 MHz, is unlikely.<BR><BR>Absent rig troubles, 75 Meter NVIS should work
very well over the ranges <BR>indicated.<BR><BR>A suitable NVIS antenna is a
dipole with the feed point at 15 feet AG and<BR>the dipole ends at 2 feet
AG. The length will be a little longer than<BR>468/f, so suggest you cut it
a little longer then tweak it on. The <BR>bandwidth will be about 100 Khz.
The feed point Impedance will vary with<BR>ground conditions - but usually
very close to 50 ohms - no tuner required.<BR>The impedance will go up, if
the ends are raised.<BR><BR>W.Wa. Section Mgr., N7NVP and I have developed a
series of NVIS designs <BR>which we presented at the NW Comm. Academy. Ed
and I have used these<BR>antennas extensively. I my case, and I'm sure Ed's
experience is the same,<BR>coverage is solid from the antenna out in a
circle with a -3db radius of 600 <BR>miles - a little farther at night. A
CD, containing Power Point<BR>Presentations of some of our NVIS antenna
work, is available via the ARRL.<BR><BR>Vertical antennas are hard to
achieve at 75, Some loading has to be used, <BR>to keep them reasonably
short, and an efficient ground is very difficult.<BR><BR>Ground Wave ---
with the stations only two miles apart, ground wave with<BR>just about
anything made of wire for an antenna and 100 watts, should <BR>produce a
readable signal on 75 or 160.<BR><BR>In the 1980's we ran a social net on
ten meters with members checking in at<BR>distances 30 or so miles. We had
antenna parties where we built 10 meter J<BR>poles. When we all got the J
Poles up, we had solid copy every night. So, <BR>maybe 10 meters and a
simple J Pole antenna would get it done.<BR><BR>Finally, Mark Yordy, W7BBO,
and I played with a full wave loop on 160 lying<BR>flat on the grd. It was
20 or 30 feet too long from 468/f. But, after we <BR>got it on 1.965, we got
excellent reports all over the NW with a 100 watt<BR>mobile rig.<BR><BR>I
hope these thought are helpful.<BR><BR>73 de Tom (W6QJI)<BR><BR><A
href="mailto:tjsand@wavecable.com">tjsand@wavecable.com
</A><BR><BR>[Non-text portions of this message have been
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clear=all><BR>-- <BR><BR>Best 73 from:<BR>regards from:<BR>CT4RK<BR>Carlos
Mourato<BR>Sines - Deserto do Jamais Ocidental<BR>(Deserto livre de
dromedários!...foram todos para a Praça do
Comércio)<BR><BR>-----------------------------------------------------------
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