Re-activating a Roof-top TV Antenna

On Jul 21, 10:40=A0pm, Joe wrote: > I would like to help a relative "re-activate" a roof-top TV antenna on a > single storey house in southern California. >

If the antenna is more than 10 years old I'd just replace it. I bought a Winegard 7082 last fall in Torrance CA for $120 which works great. If you're in a 'hole' hiding behind a hill you'll want at least enough height to clear the obstructions. Digital TV isn't too forgiving of dynamic multipath though the newest receivers are much better. Come next Feb your antenna will need to get channels 7 through 51 to get all the DTV in LA so the 7082 will be much bigger in size than what you'll need. The Winegard HD7694 is 35" wide vs 110 for the 7082 and the boom length is 65" vs 110" and will have plenty of gain in the LA area. If you're in Orange County a preamp on the antenna might be helpful. RG-6 size cable is a good idea though the best RG-59 size like Belden 1505A comes very close and is a little lighter. Some links to help.

G=B2

I would also recommend a visit to

You plug in your address and you get a list of all the transmitters in your area, pre- and post-digital-transition, sorted in descending signal strength order. It also shows the azimuth of each transmitter from your location, which is useful in pointing your antenna.

Jerry

I'd suggest that you read through the information available at

- it was apparently compiled by ChannelMaster based on installers' experiences. It goes over a lot of the procedures you'll need to consider.

Stark Electronics is a good source for many of the materials you'll need. Markertek is another.

First thing to do: examine the current mast and guy-line arrangement. Then, look at the power-line configuration on the building, and all buildings nearby. See if you can figure out any remotely plausible way that the antenna or its guy wires could fall onto (or close to) any power line(s) when you are lowering it or raising it. If so,

*STOP*. Do not proceed, pass Go, or collect $200. Get a professional installer to do the work for you. People die every year or so when antenns they are working on hit power wiring... don't add to the casualty list, please!

Now, as to your specific needs.

Depending on the relative locations of the TV transmitters you want to receive well, you may want to consider installing a remote-controlled antenna rotator.

For a downfeed cable, I would recommend using RG-6 cable (it's thicker and has lower losses than the thinner RG-59 used in most indoor hookups) with multiple shields. I would recommend purchasing a "quad-shield" RG-6 intended for satellite-dish applications... this is designed to have very low losses and excellent shielding properties, and it's not much more expensive than the cheap stuff. Belden

7916A is one such... there are plenty of others.

You'll also need a set of F connectors to crimp or clamp onto the ends of the cable, after you cut it to length. The Paladin SealTite connectors are advertised as being weathertight/waterproof; a proper crimping tool is required. I believe that there are slide-on / clamp-on F connectors which are similarly weather-resistant but I don't know a specific model number to suggest. In any case, make sure you match the type of connector to the type of cable (both the RG size, and the shield configuration) - different connectors are used for single, double, and quad-shielded RG-6 cables.

75-to-300-ohm matching transformers / baluns are easily come by, and I don't know that there's much reason to prefer one brand to another. Just make sure you buy one rated for outdoor use.

You'll want a static-discharge block (a.k.a "antenna discharge unit" or "lightning arrestor") at the point at which the cable enters the house. You'll need a short, direct, heavy-gauge wire from the discharge block to a lightning ground (e.g. a 10' ground rod hammered into the earth). If you install a new ground rod, national (and probably local) electrical codes require that you "bond" it to your main building ground system... this generally involves installing a direct heavy-gauge wire run from the new ground rod to the building power entrance ground, connected using exothermic welding or split-bolt connectors (not soldering!).

I prefer to add some additional weatherproofing to the F connectors after the cables are connected to the discharge block and the matching transformer. My current favored technique is to use self-amalgamating rubber tape ("Stretch-n-seal" or a similar product), and then paint this with liquid-PVC "liquid electrical tape" and allow to dry.

When you connect the cables (from antenna and from inside the house) to the discharge block, run the cables down *below* the block and then back up to it... create a "drip loop" in each cable. This will ensure that water which hits the cable flows off to the ground, and not into the house or into the equipment.

As to lowering the antenna... make sure you have enough trained people, with enough muscle to do the job safely. Safety first! You'll probably need to release two of the guy wires where they're fastened to the roof, brace the bottom of the mast, release whatever clamps are holding the mast to a chimney (or whatever), and then "walk" the mast and antenna down to a horizontal position. Having a portable sawhorse up on the roof, to support the top of the mast, will keep the antenna elements from hitting the roof and bearing the weight of the antenna and mast (and possibly breaking). An antenna and 20' mast can be heavier than you expect, and is rather unwieldy!

If the antenna itself is in good shape, you can simply remove the old matching transformer and feedline, install the new ones, and put the antenna back up. Might be a good idea to gently burnish the electrical contact bolts and washers (e.g. with a green scrubbing pad) to remove surface oxidation and corrosion, and apply a dab of an aluminum-compatible anti-oxidant cream (e.g. Penetrox or NoAlOx) before connecting the matching transformer.

However, if the antenna has been up in the air for a decade or two, you may find that the aluminum elements and fitting are suffering from significant corrosion (especially if you're near enough to the coastline to have some sea-salt in your air) and the plastic insulators may be cracked and brittle from long exposure to sunlight. If so, you may want to replace the antenna itself.

Attaching the feedline to the mast at several points, using heavy-duty UV-resistant black cable ties, would probably be a good idea. Leave some slack at the top so the cable isn't under stress.

Walk the antenna back up, reattach the guys, aim the antenna in the desired direction, re-clamp.

--
Dave Platt                                    AE6EO
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