[mythtv-users] Antennas

[Stephen P. Villano]

On 11/15/13 2:40 PM, Joseph Fry 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.
Older homes in the US do not have ground rods in many areas. The ground
was accomplished using water pipes. In that case, it is strongly
recommended to install at least an 8 foot grounding rod (deeper if you
are in a dry area).
> 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.
When bonding those grounds, do not be surprised if you see a spark when
connecting them. I've personally dealt with grounds 50 feet apart having
100+ volt differential between them, hence why one bonds the grounds
together.
> 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!
> _______________________________________________
>
True, but carried away in a good way. This is critically important
information that is all frequently not known or understood.

I'd have mentioned the suggestion of the OP of putting a lightning rod
above the antenna being a really bad idea as well.
That would cause extremely high induced voltages into the antenna line.
Burning down the home kinds of current flowing.

Good catch on that zip line as well. That is useful only for household
appliances, not for RF signal! It'd be amazing if the signal actually
made it down due to capacitive losses!