[mythtv-users] Attic Antenna: simple question.

[blind Pete]

On Sun, 7 Sep 2014 08:21:39 -0500
"Saul A. Peebsen" <jaglover at gmail.com> wrote:

> On Sun, 7 Sep 2014 12:24:45 +1000
> blind Pete <0123peter at gmail.com> wrote:
> 
> > On Sat, 06 Sep 2014 13:18:44 -0400
> > Bert Haskins <bhaskins at chartermi.net> wrote:
> > 
> > > 
> > > I have been trying to recover at least a few channels after
> > > charter effectively  bricked my HDHR. One, CH8 is marginal and in
> > > an attempt to improve it I want to modify a existing antenna. The
> > > antenna has all of the elements including the center point of the
> > > dipole connected (grounded) to the main beam which then is bolted
> > > to the grounded mast. This just doesn't seem right to me, i.e. it
> > > seems like the dipole should be insulated from all the other
> > > parts(?). I've searched the net and found lots of other
> > > information but nothing on this.
> > 
> > Antenna design is a bit of a black art.  
> > 
> > With a Yagi-Uda design all of the directors and the reflector are 
> > simple conductors insulated from the boom.  There might be a bunch 
> > of plastic washers and sleeves where they are not obvious to the 
> > casual glance.  
> > 
> > If you doubled the length of the passive elements there 
> > would be a node at the centre, so electrical connection 
> > would be OK.  But that would make the antenna twice as 
> > large as necessary.  Such a design would surprise me.  
> > 
> > With a log-periodic antenna there are two parallel booms.  half 
> > of the elements are electrically connected to one and the other 
> > half are connected to the other.  
> > 
> > Many, many, weird and wonderful designs are possible.  
> > 
> > If you like mucking about with this stuff, go for it.  
> > 
> > If you just want a marginal signal to be a bit better 
> > consider buying a new (corrosion free), slightly larger antenna.  
> > Make sure that it is pointing in the right direction.  
> > Check that there are no obstructions, hills, neighbour's 
> > new attic, wet trees, etc.   Yes, at some frequencies a mess 
> > of leaf sized conductors will block a signal.  Dry leaves 
> > don't conduct enough to matter.  Then all of the usual stuff, 
> > check the cables and connectors.  Is anything generating 
> > electronic noise nearby?  
> 
> I've used Yagi antennas where all elements are grounded in the middle.
> Dipole is not insulated. As much I remember of this type of design
> insulation is not necessary because there is never any voltage in
> center point (although it is the point of max current).

What I should have written was; if it looks like it was electrically 
connected, then it is probably supposed to be, if it looks like it 
is insulated, then it is probably supposed to be.  

The design possibilities are endless.  Now that you have brought it 
to my attention, I'm not so confident about the Yagi.  Possibly 
it just does not matter in that case.

-- 
testing
bP