[mythtv-users] Attic Antenna: simple question.
Bert Haskins
bhaskins at chartermi.net
Mon Sep 8 01:13:02 UTC 2014
On 9/7/2014 8:36 PM, Tom Poe wrote:
> On 09/07/2014 04:40 PM, Daryl McDonald wrote:
>>
>>
>> On Sun, Sep 7, 2014 at 2:36 PM, Bert Haskins <bhaskins at chartermi.net
>> <mailto:bhaskins at chartermi.net>> wrote:
>>
>>
>> On 9/7/2014 1:45 PM, Daryl McDonald wrote:
>>>
>>>
>>> On Sep 7, 2014 9:23 AM, "Saul A. Peebsen" <jaglover at gmail.com
>>> <mailto:jaglover at gmail.com>> wrote:
>>> >
>>> > On Sun, 7 Sep 2014 12:24:45 +1000
>>> > blind Pete <0123peter at gmail.com <mailto:0123peter at gmail.com>>
>>> wrote:
>>> >
>>> > > On Sat, 06 Sep 2014 13:18:44 -0400
>>> > > Bert Haskins <bhaskins at chartermi.net
>>> <mailto: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.
>>>
>> You are preaching to the choir on that point!
>> Sixty-five years in electronics and I still many many more questions
>> than answers where antenna are concerned.
>>>
>>> > >
>>> > > 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.
>>>
>> Q. Does mild surface corrosion affect the signal?
>>
>>> > > 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).
>>> >
>>> > --
>>> > Cheers, Saul
>>> > _______________________________________________
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>>>
>>> Since E = I x R, how can there be no voltage (E) and max current
>>> (I) at any point?
>>>
>> Impedance.
>> 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.
>> 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.
>>
>> Please replace "dipole" in my original question with "folded
>> dipole"... yet another senior moment.
>>
>>>
>>>
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>>
>>
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>> Forgive my oversight 0 = infinity x 0, may I claim the senior moment
>> too?
>>
>>
>>
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> Unfortunately, I know nothing that could contribute to this
> discussion. Is this antenna purposed to pull in digital television
> signals?
Yes
> 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
I've built a Hoverman and got better results with a DIY quad bowtie.
I'm gathering parts to do the dual quad variation.
> with a pre-amp booster. What is an antenna used for with Comcast cable?
So that I can keep using my HDHR and record more that one channel and
edit the recordings.
Plus the sound is much!!! better with OTA.
Better than 90% of what I record is just for time-shifting.
> Are you looking for digital over the air reception on your mythtv setup?
I am getting four out of the five channels that I care about.
Only two of these are easy to get.
> Tom
>
>
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