[mythtv-users] Antennas

Daryl McDonald darylangela at gmail.com
Fri Nov 15 19:57:15 UTC 2013


Yes you did, but thanks again, it was a wonderful excursion!

On Fri, Nov 15, 2013 at 2:40 PM, Joseph Fry <joe at thefrys.com> wrote:
>>>> My antenna (homemade) is supported by 3/4" pvc conduit, 3' into the
>>>> ground and attached to the eave trough support and tethered with guy
>>>> ropes. In windy conditions I have observed sway of 2", maybe 3" with
>>>> little or no effect on my signal. I would bet your tree will have
>>>
>>> PVC makes a great mast for a short period of time (maybe a couple of
>>> years).  It becomes very brittle when exposed to prolonged UV light.
>>> A coat of Krylon or similar paint helps immensely.
>>>
>>>> greater sway, which is likely to have adverse effect for you. What
>>>> happens when your tree grows and bursts your zip ties, or whatever
>>>> fasteners you might use?
>>>
>>> Last I checked, trees grow by adding layers to the outside, not by
>>> expanding.  Typically a tree will simply grow around a fastener rather
>>> than bursting it.  Though zip ties my still burst as most fare even
>>> worse when exposed to UV.
>>>
>>> Putting an antenna in a tall tree is actually a very doable solution
>>> assuming you have a suitable tree.  You will still want a mast that
>>> lifts the antenna above the foliage, and be prepared to adjust it
>>> annually, but I know for a fact that many old HAM's and CB junkies
>>> would do exactly that if they had a nice tall straight pine that was
>>> easily climbed.
>>>
>>> As far as wind causing swaying impacting your reception... I wouldn't
>>> worry about it unless your in a deep fringe area, using a highly
>>> directional antenna, where being a few degrees off will kill your
>>> signal.  What wind may do is cause interference, and it won't matter
>>> if your in the tree or not.  There are three known/assumed causes of
>>> wind related interference.  First is that it increases scatter
>>> radiation (weak signals reflected off leaves of other trees, etc)
>>> which makes for an ever changing multipath signal that the tuner
>>> simply can't compensate for.   The other is that wind may cause an
>>> increase the amount of static buildup on your antenna/mast and other
>>> surrounding surfaces; this buildup and subsequent discharge is what
>>> some believe causes wind related dropouts.  Finally, when wind blows
>>> it stirs up dust/pollen/water droplets/etc., even a small amount of
>>> particulates in the air can impact reception.
>>>
>>> I would say that if putting the antenna in a tree will give you line
>>> of sight that you wouldn't be able to achieve with an affordable and
>>> typical mounting solution , then put it in the tree.  Getting above
>>> the treetops and achieving line of sight will help you more than
>>> having an antenna that doesn't move at all but must penetrate trees or
>>> rely on defraction/scatter to lock a signal... both of which would be
>>> far more subject to problems with wind.  If you can simply mount the
>>> antenna to your roof and have line of sight, than put it on the roof,
>>> far easier to service there.
>>>
>>> JUST BE SURE TO GROUND YOUR ANTENNA AND MAST!!!!
>>
>> Thanks for the suggestion Joseph, how would you recommend grounding
>> it? As it stands, pun intended, the two terminals of the antenna run
>> inside the conduit on stranded copper lamp wire, and into the house. I
>> haven't grounded it as yet not knowing how to achieve a good ground
>> without interfering with the signal. Maybe a separate lightning rod,
>> mounted higher than the antenna, and copper to the ground?
>
> First of all... get rid of the lamp wire.  At very least get some good
> 300 Ohm twinlead (there is a difference), but highly recommended is
> getting a good balun and run some RG6 Coax all the way up to the
> antenna.  Using anything other than coax cable results in your wiring
> acting like an antenna, which can cause issues.
>
> Next you need to decide if your going to install a new grounding rod,
> or use the one your house already has.
>
> 1. If your antenna is anywhere near your home's electrical panel, it
> is far easier to use the home's ground.
> 1.1. If you don't see the ground rod it may be buried, you should see
> a 6 guage or larger cable running from your panel into the ground
> outside just dig it up and follow it, shouldn't be too long.
> 2. If your antenna is far away from your electrical panel, you may
> want to install a new grounding rod.
> 2.1 Install an 8 foot or longer rod straight into the ground so only 2
> or 3 inches are exposed.
> 2.2 You will need to run a 6 guage or larger copper or aluminium
> ground wire between the new rod and your homes existing rod to "bond"
> them ; bonding the ground rods is important as you want the same
> potential energy at both the antenna and home grounds.
>
> Next, you need to ground the antenna/mast.
>
> 1. If your mast is conductive, drill a hole  part way up the topmost
> mast section and thread in a self tapping screw to act as a terminal
> for the ground wire.
> 2. If your mast in not conductive, you need to ground to the actual
> antenna body, again tap your own hole for a screw if none exists.
> 3. Run a 10 gauge copper or aluminum ground wire between the
> antenna/mast and your ground rod, clamping it firmly at both ends
> (they sell cheap clamps for the grounding rod)
>
> Finally, you need to ground the actual antenna leads (wiring).
>
> 1. Install a grounding block inline with your coax (or if you went
> twin lead you need a "static discharge unit")  this should be placed
> close to the point where the wiring enters the home,
> 2. Run a dedicated 10 guage solid ground wire between the grounding
> block and the grounding rod.
>
> Notes:
> Do NOT daisy chain your ground wires.  Each grounded piece should have
> a dedicated run to the grounding rod.
> Do NOT have any sharp bends in your grounding wires.
> Feel free to bury your ground wires in a shallow trench to keep them safe.
> Clean all ground contact points (antenna, rod) with a bit of sand
> paper to remove any corrosion that may prevent good conductivity.
>
> Grounding properly is not fun, but it is essential.  Not just to
> protect from lightning either, as the grounds serve to reduce noise (a
> very simplistic way to describe it), and can make it far easier to get
> a good clean signal.  If any one of the above steps is ignored, it can
> severely impact your reception, not to mention burn down your house.
>
> For example, if you don't bond your two ground rods and lightning
> strikes your antenna, it will take a little while for the ground rod
> to dissipate all of that charge, so your two ground rods are at
> different energy levels.  Thus, your tuner's chassis ground is at one
> level because it's connected to the home's grounding rod, the
> transmission line's ground level is at a higher level since its on the
> other rod, and now current flows from the antenna through the tuner
> chassis, and out to the home's ground and boom there goes your tuner,
> and possibly other devices plugged in the same circuit.  If they are
> bonded with a large ground wire, the home's grounding rod, and thus
> the tuner's chassis ground, is the same as the antenna's thus no
> current would flow as there is no potential between them.
>
> Wow I got carried away!
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