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<div class="moz-cite-prefix">On 09/07/2014 04:40 PM, Daryl McDonald
wrote:<br>
</div>
<blockquote
cite="mid:CAMwtTBDCqFT96j=y8JDm_p4ZcHziqpgmpyL9r_LQO=hd47_H3Q@mail.gmail.com"
type="cite">
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<div dir="ltr"><br>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Sun, Sep 7, 2014 at 2:36 PM, Bert
Haskins <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:bhaskins@chartermi.net" target="_blank">bhaskins@chartermi.net</a>></span>
wrote:<br>
<blockquote class="gmail_quote">
<div><span class=""> <br>
<div>On 9/7/2014 1:45 PM, Daryl McDonald wrote:<br>
</div>
<blockquote 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" target="_blank">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"
target="_blank">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"
target="_blank">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>
</span> 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.<span class=""><br>
<blockquote 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>
</span> Q. Does mild surface corrosion affect the
signal?<span class=""><br>
<br>
<blockquote 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>
>
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<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>
</span> 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.<span
class=""><br>
<br>
<blockquote type="cite">
<p dir="ltr"> </p>
<br>
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</blockquote>
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<div>Forgive my oversight 0 = infinity x 0, may I claim the
senior moment too?</div>
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</pre>
</blockquote>
Unfortunately, I know nothing that could contribute to this
discussion. Is this antenna purposed to pull in digital television
signals? I live 72 miles from Minnesota tv farm. Line of sight is
minimal, so signals are strong enough late at night, but reception
is poor during the day. My attic antenna is a DIY Hoverman with a
pre-amp booster. What is an antenna used for with Comcast cable?
Are you looking for digital over the air reception on your mythtv
setup?<br>
Tom<br>
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