Tech- Tune up your TV antenna

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In my last post on television- TV in your RV, I pointed out that the standard Winegard “Sensar” (a.k.a. “Batwing”) antenna works very well for the new digital tv signals (and, by extension, works well for the digital HD signals).

But… what to do when you cannot get the stations that your neighbor can, or when the antenna gets a bit stuborn while cranking it up, down, or turning it.

Luckily, troubleshooting these antennas is pretty easy, and along with some regular maintenance, the Sensar will give years of top notch viewing enjoyment.

Let’s take a look at the basic of maintenance and repair for antenna and coax cable….

Mechanical Maintenance

The first item to cover is regular maintenance- something everyone should be doing, whether you have problems or not. This should be done on a fairly regular schedule- a good time to do this is on a twice yearly inspection of the roof sealant (you do need to get on the roof to do this….. don’t fall off!).

These pictures are from the Sensar owners manual, which you can download from http://winegard.com/mobile/sensar.htm - if you don’t have a copy, download, print and read the manual…. it answers a lot of questions.

You want to use a pure silicone spray lube to do this… not WD-40 or any lubricant that contains petroleum products!

The reasons for this are two fold- if you have an EPDM (rubber) roof, you don’t want the petroeum getting on the membrane, and the worm gear that elevates the Sensar uses an EPDM set of washers to seal out water… using a petroleum based lube will destroy this set of washers, resulting in leaks. Simply praying the gears and base with silicone lube will eliminate the “chunka-chunka-chunka” that you sometimes get when lowering the antenna, and keep the washers that provide the seal intact- protecting you from leaks.

Electrical Tune-up

(and Coax cable repair)

As I have often said- the Winegard Sensar is an excellent antenna (here at our shop, they outperform a large 12 foot multi-element “deep-fringe” antenna we had, which was much higher than the Sensars).

There are only a few things that can go wrong with the Sensar and by far the most common is a problem with the coaxial cable , there are generally 2 types of coax used for Television signals, RG-6 or RG-59 . Winegard uses RG-59 for the short length of cable that comes pre-attached- the reason you need to know that is that the end F connector is different for each type of cable- RG-6 is larger than RG-59.

The Sensar comes in 2 versions, an unamplified and an amplified version. By far the most common version is the amplified model, which usually (but certainly not always) has a wall plate with a switch and an LED power indicator.

If you notice in the illustration, the coaxial cable is both carrying the signal from the antenna to the power supply, and carrying 12 volt power from the power supply to the amplifier in the antenna. Most problem I run in to with this setup is due to a bad connection right at the antenna, so that the amplifier is not getting power.

Luckily, this is easy to diagnose- simply turn the power switch on, unscrew the coax from the antenna head, and check to see if you have 12 volts between the center conductor and the shield (outside). 90% of the time, this connection will be the problem- the other 10% of the time, it will be in the first splice, which is sometimes hard to access. The first (and usually only) splice in this cable will be right under the roof plate inside the roof. If you are lucky, you can pull it out (carefully) through the entrance hole in the plate- if not, you may have to remove the inside crank assembly and fish around for it a bit.

This brings up the issue of the “F” connectors themselves and how to properly install them There are several types of connectors, but only 2 types are really good enough to use- the hex crimp and the compression type. There is a twist on type as well, but the twist on is only useful in an emergency repair- for a variety of reasons they are simply not very good- including the fact that we are running 12 volt power through them, and the sharp threads in the barrel tend to simply cut the shield wires.

The hex crimp and the compression type are both very good when done properly, but doing them properly requires going out and buying the right tools (for me, “having” to buy a new tool is a good thing - for some it may not be). I would recommend buying the compression type tool, for a couple of reasons. First- the “economy” compression tool does just as good a job as the expensive models, and many (if not most) professional installers use compression fittings, because they tend to be naturally more weather resistant, and make a good, firm connection. Unfortunately, the economy crimp type tools don’t make a hex crimp, they make a round crimp, with “ears”,which distorts the cable enough to cause problems sometimes, and isn’t very secure. Economy compression tools can be found at most large home center type stores for under $20 (the tool in the picture was purchased at Lowes for a bit under $50, it will work on many different brands of compression connectors).

The next tool which is nearly mandatory is a good coax stripper. Now, you might question the need for a special stripping tool that just works on coaxial cable, but, while it is posssible, it is very, very hard to prepare a coax cable properly for connection without one.

Why? The answer is that not only does a good coax stripper strip all of the layers of the cable to the right length, but it does that without nicking the center conductor. because the senter conductor of an antenna coax cable carries very high frequency electricity, it is subject to something called the skin effect, which is that very high frequency signals travel just on the very outside skin of a conductor. A nick in this conductor will cause the signal to reflect backalong the cable, causing reduced signal reaching the television.

The skin effect is so pronounced that a lot of RG-6 cable has a center conductor of steel, with copper plating- the steel is simply there for stregth, and the copper plating carries the entire signal.

These thumbnail images are of of a good coax stripping tool (under $15), and properly prepared coax cable- ready for installing either a hex crimped or compression F connector.

A few tips-

• If you need to buy coax cable, either RG-59 or RG-6, look on the jacket for the specs- most RG-6 cable is spec’d at 2.5 to 3 gigaherz, which isn’t needed for regular TV signals, but is needed for satellite signals, and some RG-59 will actually meet this spec. You can never have too much bandwidth.
• When you have to figure out which cable goes where, I use a multimeter set on Ohms, and a small jumper cable with sligator clips. I then measure the resistance between the center and shield, then shirt them out with the jumper and measure again. When I find the one with near zero resistance, I know I’ve found the right cable.
• Never try to push a meter probe in to a female F connection- it will probably fit, but you will distort the spring metal inside the connector. I cut a short piece of cable and use the center conductor to insert in to the F connection.
• Clean and shiney- the signal currents we are dealing with are tiny- the smallest bit of corrocion can mean the difference between getting a picture and not.

With a bit of maintenance, you can get better “off the air” reception than any of your neighbors- and with the new digital transmission, you can get better reception than either cable or satellite, if you simply follow the basics!

Last 5 posts by Chris Bryant

• Water Pump Troubleshooting - May 29th, 2008
• Tech- TV in your RV.... - May 21st, 2008
• Tech- Tune up your rooftop A/C - May 8th, 2008
• Tech- Inside a Dometic NDA1402 - April 17th, 2008
• Maintenance- Cleaning a Norcold Burner - April 2nd, 2008

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