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<div class="moz-cite-prefix">On 9/7/2014 1:45 PM, Daryl McDonald
wrote:<br>
</div>
<blockquote
cite="mid:CAMwtTBCiZ1U53Ua-R_MgQQijnUBYE1zYA6_1U4WNn-+i7Xq6KQ@mail.gmail.com"
type="cite">
<p dir="ltr"><br>
On Sep 7, 2014 9:23 AM, "Saul A. Peebsen" <<a
moz-do-not-send="true" href="mailto:jaglover@gmail.com">jaglover@gmail.com</a>>
wrote:<br>
><br>
> On Sun, 7 Sep 2014 12:24:45 +1000<br>
> blind Pete <<a moz-do-not-send="true"
href="mailto:0123peter@gmail.com">0123peter@gmail.com</a>>
wrote:<br>
><br>
> > On Sat, 06 Sep 2014 13:18:44 -0400<br>
> > Bert Haskins <<a moz-do-not-send="true"
href="mailto:bhaskins@chartermi.net">bhaskins@chartermi.net</a>>
wrote:<br>
> ><br>
> > ><br>
> > > I have been trying to recover at least a few
channels after charter<br>
> > > effectively bricked my HDHR. One, CH8 is
marginal and in an attempt<br>
> > > to improve it I want to modify a existing
antenna. The antenna has<br>
> > > all of the elements including the center point of
the dipole<br>
> > > connected (grounded) to the main beam which then
is bolted to the<br>
> > > grounded mast. This just doesn't seem right to
me, i.e. it seems<br>
> > > like the dipole should be insulated from all the
other parts(?).<br>
> > > I've searched the net and found lots of other
information but<br>
> > > nothing on this.<br>
> ><br>
> > Antenna design is a bit of a black art.<br>
</p>
</blockquote>
You are preaching to the choir on that point!<br>
Sixty-five years in electronics and I still many many more questions<br>
than answers where antenna are concerned.<br>
<blockquote
cite="mid:CAMwtTBCiZ1U53Ua-R_MgQQijnUBYE1zYA6_1U4WNn-+i7Xq6KQ@mail.gmail.com"
type="cite">
<p dir="ltr">
> ><br>
> > With a Yagi-Uda design all of the directors and the
reflector are<br>
> > simple conductors insulated from the boom. There
might be a bunch<br>
> > of plastic washers and sleeves where they are not
obvious to the<br>
> > casual glance.<br>
> ><br>
> > If you doubled the length of the passive elements
there<br>
> > would be a node at the centre, so electrical
connection<br>
> > would be OK. But that would make the antenna twice as<br>
> > large as necessary. Such a design would surprise me.<br>
> ><br>
> > With a log-periodic antenna there are two parallel
booms. half<br>
> > of the elements are electrically connected to one and
the other<br>
> > half are connected to the other.<br>
> ><br>
> > Many, many, weird and wonderful designs are possible.<br>
> ><br>
> > If you like mucking about with this stuff, go for it.<br>
> ><br>
> > If you just want a marginal signal to be a bit better<br>
> > consider buying a new (corrosion free), slightly
larger antenna.<br>
</p>
</blockquote>
Q. Does mild surface corrosion affect the signal?<br>
<br>
<blockquote
cite="mid:CAMwtTBCiZ1U53Ua-R_MgQQijnUBYE1zYA6_1U4WNn-+i7Xq6KQ@mail.gmail.com"
type="cite">
<p dir="ltr">
> > Make sure that it is pointing in the right direction.<br>
> > Check that there are no obstructions, hills,
neighbour's<br>
> > new attic, wet trees, etc. Yes, at some frequencies
a mess<br>
> > of leaf sized conductors will block a signal. Dry
leaves<br>
> > don't conduct enough to matter. Then all of the usual
stuff,<br>
> > check the cables and connectors. Is anything
generating<br>
> > electronic noise nearby?<br>
><br>
> I've used Yagi antennas where all elements are grounded in
the middle.<br>
> Dipole is not insulated. As much I remember of this type of
design<br>
> insulation is not necessary because there is never any
voltage in<br>
> center point (although it is the point of max current).<br>
><br>
> --<br>
> Cheers, Saul<br>
> _______________________________________________<br>
> mythtv-users mailing list<br>
> <a moz-do-not-send="true"
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href="http://www.mythtv.org/mailman/listinfo/mythtv-users">http://www.mythtv.org/mailman/listinfo/mythtv-users</a><br>
> <a moz-do-not-send="true"
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> MythTV Forums: <a moz-do-not-send="true"
href="https://forum.mythtv.org">https://forum.mythtv.org</a></p>
<p dir="ltr">Since E = I x R, how can there be no voltage (E) and
max current (I) at any point?<br>
</p>
</blockquote>
Impedance.<br>
E and I are shifted in respect to each other so at a given point in
time you can have zero voltage and max current at a given point.<br>
There are many good explanations on the net and this is but one of
the many things that puts antennas in the "black art" category. <br>
<br>
Please replace "dipole" in my original question with "folded
dipole"... yet another senior moment.<br>
<br>
<blockquote
cite="mid:CAMwtTBCiZ1U53Ua-R_MgQQijnUBYE1zYA6_1U4WNn-+i7Xq6KQ@mail.gmail.com"
type="cite">
<p dir="ltr">
</p>
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