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<H3 class=h3><FONT size=5>Outdoor MF and HF Antenna</FONT> </H3><IMG
style="BORDER-RIGHT: black 1px solid; BORDER-TOP: black 1px solid; BORDER-LEFT: black 1px solid; BORDER-BOTTOM: black 1px solid"
height=346 alt="VE7BPO Antenna System"
src="http://www.qrp.pops.net/images/before%202008/SWL-ANT.GIF"
width=449><BR><BR>
<P><FONT face=Tahoma>The schematic to the left summarizes the outdoor VE7BPO MF
and HF receiving antenna system for summer 2007. Although modest for a big city
lot, this antenna seems to pull in the DX and is relatively free of RFI. This
antenna was just a case of "putting as much wire in the sky as possible" and the
dimensions are indicated for interest sake only. The 27 meter long horizontal
section is supported between 2 trees at a height of about 14 meters high. The
weight of the vertical element wire plus slack in the horizontal wire droop it
to about 13 meters high in the center. The vertical section is soldered to the
horizontal wire 6 meters from the nearest anchoring tree and runs straight down
to the antenna feed point which is about 1 meter off the ground. The feed point
is a piece of copper-clad PC board (with isolated sections created with a
hobbyist motor tool) and is bolted to a long copper pipe which serves as the
first station earth-grounding stake. A transformer (T1) configured as a UNUN
<STRONG>(unbalanced-to-unbalanced)</STRONG> is used to interface the antenna
with 50 ohm coax that runs through the house and into the radio shack. Some
rudimentary experiments with the UNUN and the earth-grounding system were
undertaken. <BR><BR>The methods I used to potentially lower unwanted RFI to my
antenna system are as follows: </FONT></P>
<OL>
<LI><FONT face=Tahoma>The receiver and power supply are independently
connected to a single, central ground point (ground buss) in the radio shack.
</FONT>
<LI><FONT face=Tahoma>6-10 gauge wire is used for my ground system (not
including the radials which are bare 12 gauge wire). </FONT>
<LI><FONT face=Tahoma>The ground wire connecting to my first earth stake to
the station ground buss is just outside the shack window and is short as
possible to provide a low impedance and low inductance path for MF and HF
frequencies. </FONT>
<LI><FONT face=Tahoma>There is a second ground stake located 1 meter from the
primary ground stake (I will add 2-4 more in time). </FONT>
<LI><FONT face=Tahoma>I have a large piece of steel buried underneath the soil
tied in to my system as well as 3 bare copper radials. The radials are 3 - 7
meters in length. </FONT>
<LI><FONT face=Tahoma>New RG58/U coax was used as the feed line. </FONT>
<LI><FONT face=Tahoma>All wire splices in the grounding system are soldered
and taped up. I used conductive grease (to prevent oxidation at the wire-stake
interface) on any clamps connected to ground stakes. My ground stakes are ~ 2
meters long. </FONT>
<LI><FONT face=Tahoma>The earth grounding area soil is moist and peat-laden
and is watered regularly. </FONT>
<LI><FONT face=Tahoma>I plan to maintain this ground system every 2
years.</FONT> </LI></OL>
<DIV><FONT face=Tahoma>Mais informações interessantes sobre UNUN de 4:1 e
9:1 em: <A
href="http://www.qrp.pops.net/swl-ant.asp">http://www.qrp.pops.net/swl-ant.asp</A></FONT></DIV>
<DIV><FONT face=Tahoma></FONT> </DIV>
<DIV><FONT face=Tahoma>Fonte: QRP / SWL Homebuilder</FONT></DIV></BODY></HTML>