Another antenna project

[Markm]

http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3d83876c7890202a

The company that I work for is doing a breakroom expansion, which will include one tv. This is a seed corn processing plant so alot of steel and metal buildings with one of the building being about 80' in height. The antenna will be mounted outside on top of a cyclone platform around 40' with a clear shot of Chicago, Il. The run of RG6 could be as far as 100-150 feet.
There could be other options as to where we mount the antenna.

What if any antenna will work with all of this steel?

In a previous post of mine at home JC recommended an XG91 with Kitztech preamp with a cs600 and my existing hpd269 preamp. I have that at home but not installed.

Thanks again,

Mark

[Tower Guy]

The antenna will be mounted outside on top of a cyclone platform around 40' with a clear shot of Chicago, Il. The run of RG6 could be as far as 100-150 feet.


The loss of 150' of RG-6 will approach 10 db. WWTO on VHF channel 10 is extremely strong, so preamp selection will be critical.

One approach is a UHF only aimed at 210 degrees with an AP4700 UHF only preamp.

If you tried for Chicago only you'd likely miss CBS. A rotator in a break room will be too confusing.

[John Candle]

WWTO channel 10 is way to strong. I recommend a Antennas Direct 91 XG , UHF only antenna with a Winegard AP4700 UHF only preamp. Install a coax ground block and ground. The Chicago stations are to weak to receive reliably. The Peoria stations are stronger , aim the antenna at about 210 degree magnetic compass. Here is how to aim antennas , http://www.kyes.com/antenna/pointing/pointing.html. Also read and understand about , REAL Digital Broadcast Tv Channels , Virtual Digital Broadcast Tv Channels , Analog Broadcast Tv Channels , http://forum.tvfool.com/showthread.php?t=695

[John Candle]

The reason for grounding the coax foil shield and shield wires , is not so much the lightning. It's WWTO 10 , the signal is so strong that need to direct the signal that is picked up by the foil shield and shield wires of the coax to ground so does not overload the tv tuner. The center wire of the coax is what carries the signal.

[GroundUrMast]

I agree with the XG-91 recommendation. If practical, mounting on top of the 80' structure may buy some precious improvement in noise margin.

I advocate grounding the coax and the mast primarily for the purpose of improved safety to people and property. http://forum.tvfool.com/showthread.php?t=901

With an antenna connected to the coax, grounding the coax shield will suppress channel 10 at the tuner in no significant way. Moving away from the ground block in either direction, there will be a point of high impedance every odd quarter-wave-length for any given frequency (assuming the ground block has an impedance of zero ohms, which it won't in practice). The signal from any RF source will still produce standing waves on the outside of the coax shield regardless of whether a grounding block is used. Standing waves on the outside of the coax shield will be decoupled at the balun / matching transformer, preventing them from significantly influencing the center conductor and shield inner surface. The antenna will receive vastly greater amounts of energy than might leak through the coax shield or balun decoupling. Without some type of inline filter to block channel 10, that energy will be coupled into the coax and delivered to any tuners connected downstream. As an analogy, grounding the coax for the purpose of suppressing strong or interfering signals would be like caulking a nail hole in the wall with no roof on the house... expecting to see the heating bill drop.

An inexpensive and effective method of suppressing channel 10 would be to insert a UVSJ. The antenna would connect to the UHF port, a termination resistor would be installed on the VHF port of the UVSJ and the common output of the UVSJ would provide minimally attenuated UHF signals and all VHF channels would be attenuated 20 to 30 dB. The previously mentions AP4700 would accomplish the same thing.

To specifically suppress channel 10 will require a tuned channel filter. Sources such as TinLee.com would be one possibility. The CM5080 Channel Master Join Tenna (http://www.channelmasterstore.com/Channel_10_Join_Tenna_Antenna_Combiner_CM0580_p/cm-0580.htm) would be a practical consumer grade option. It would connect in a manner similar to the UVSJ, the antenna would connect to the 'All Channel' port, the 'Channel 10' port would be terminated.

[John Candle]

Grounding the coax does suppress and direct to ground unwanted manmade transmissions of all kinds , electric , electronic , magnetic . And grounding the coax does suppress and direct atmospheric electric static and magnetic build up to ground. This information and almost every thing else is look up able on to internet.

[GroundUrMast]

Grounding the coax does suppress and direct to ground unwanted manmade transmissions of all kinds , electric , electronic , magnetic . And grounding the coax does suppress and direct atmospheric electric static and magnetic build up to ground. This information and almost every thing else is look up able on to internet.

I'll agree that connecting the coax shield to a low impedance ground will hold the shield near ground potential for a fraction of a wavelength along the coax. At DC and power line frequencies, that will include the full length of the coax in most installations. At 195 MHz (TV CH-10) a full wave length is a bit more than 1.5 meters. Effective grounding of that frequency will extend significantly less than one quarter of that distance from the ground block with a zero impedance connection to a perfect ground.

Please cite some credible sources that can explain how the inductance and capacitance of the coax shield can be selectively ignored.

[Markm]

JC TG and GUM,

Thanks for the recommendations! I will post the results when the project is complete.

Thanks again,

Mark