barovelli.com | 75 Ohm Scanner Coax Installs

Installing coax for your scanner - 1995

While most scanner radios and antennas are rated at 50 ohms, you may still get good results by using common CATV 75 ohm coax for your receiver. A look at this chart from the Belden catalog shows:

dB loss per 100 ft:

	50 MHz	100 MHz	400 MHz	1000 MHz
9913	.9	1.4	2.6	4.5
RG6	1.2	1.8	5.1	8.3
RG59	1.8	2.8	7.5	10.0
RG8	2.2	3.0	6.5	12.0
RG8m	2.2	3.0	7.5	13.0
RG58	4.0	5.3	12.0	22.0

I chose RG6 for my scanner antenna lead in, for the obvious reasons of availability, familiarity, and ease of connector installation . Availability. Found anywhere, RG6 is widely used in CATV installations, off air antennas, studio use, and limited use in amateur radio setups. My familiarity with the coax comes from 15 years as a CATV installer.

Connector installation requires no soldering, and by using the proper connectors and installation techniques, you get an FCC approved, highly weather resistant connection. By using CATV 'F"' connectors, you can open up a wide variety of equipment available for CATV/Antenna use to your scanner setup. This includes splitters, ground blocks, A/B switches, attenuator pads, and line amplifiers. Adapters are available for changing an F Connector to most anything.

Case in point: My installation consists of a Realistic PRO-2004, A RS Discone (Modified with a low-band whip), 120 feet of RG6 dual shield (foil and aluminum braid, not the studio 'Quad Shield' stuff), one typical ground block, two adapters-one UHF to F and a F to BNC, and an old attenuator switch box that came out of an old piece of test equipment, this gadget has 6 toggle switches on the front, and BNC in-out connections. I can throw the switches and kick in 6 to 80 dB worth of attenuation. The reason for the attenuator is so that the Solano County Sheriffs are on the same freq. as the Monterey PD, and here in Pacific Grove, I needed some way to lockout the SCSD, without affecting MPD, and this fills the bill. When I'm trying to see what's up in the Bay Area, (100+ miles away) I can easily switch out the pads.

Handling Coax
While RG6 is a rugged medium, you should stick to a few basic common sense rules. Pay strict attention to all the warnings that pertain to keeping clear of power lines. Also borrow from the rules in the CATV biz, keep the wire at least 8 feet above any walkway, and don't make any tripping hazards by laying it on the ground or suspending it from chimney to vent to drain pipe or whatever. You certainly don't want to trip while on a roof. Electrically, it is important not to bend the coax to more than a 4" radius, or crush the coax by using staples, bent nails, cinching down cable ties, or by repeatedly walking on it. CATV signals typically run from 80 to 450 MHz, and may not be affected by such stress, but one kink in the cable may cause a 'suckout' anywhere in the frequency spectrum, causing a loss in signal in probably you r favorite band.

Color Matters... In outdoor installations, stick with black insulated cable, for the white or beige cables are not U/V proof, they will harden and crack (and corrode) when exposed to sunlight.

Sources for RG6 Coax
Use a quality coax, rated 3 to 900+ MHz, with a dual shield of foil and braid. I use aluminum shielded coax, with a copper plated steel center conductor. Common sources include TV/Electronics supply stores and
Electricians Supply stores (they can get neat 500 foot "Pay out Pak" boxes of cable)

Connectors
The advent of strict FCC rules pertaining to CATV signals causing interference to off-air services has begot an abundance of connector styles. While the best are usually only available to the trade, some consumer level equipment is comparable. The widely used F connector with the 1/2" shoulder is a good choice. This connector requires the use of a Hex Crimper to attach it. A good rule of thumb is to try and pull it off with your bare hands. A well installed connector requires a good tug to remove. Use of a cable prep tool to trim the end is advisable, properly adjusted, it will automatically trim the braid to the proper length, and not score the center conductor. Tighten the connector finger tight, then about 1/4 to 1/3 more with a wrench. When the main body of the connector (not the threaded part) is snug to the port, you should not be able to wiggle or twist it. Stay away from the two-piece type connectors, as well as the twist-on types.

In outdoor use, to weather-proof the connectors, a simple rubber weather boot (looks like a spark-plug boot), filled with automotive type silicone grease (YES, GREASE) can keep the connection water resistant, while allowing access at a later date without having to peel away layers of tape or RTV from the connection. Tape and RTV eventually allow water ingress, and help keep it in.

Connector Sources
Get the right connector for the coax you use, for it is a absolute pain to force a connector on to the wrong coax. If you use RG6, get RG6 connectors. The connectors for quad shield or RG59 are different in size, and while may be forced to fit, will result in a substandard installation. The same sources for the coax apply to the connectors.

Other Items
Splitters, Ground Blocks, A/B switches, etc., should all be rated for CATV use, this gets you a higher quality type of equipment, for it must meet the FCC specs for leakage.

Hardware to keep your coax in place is found in the antenna installation section of the TV/Electronics store, when buying attachment hardware, look to see what size cable it is made for. You can get some nice little nylon clips with stucco nails attached to them , but remember to get the ones for the proper size cable, they come for both RG59 and RG6. I don't recommend using a staple gun, you may crush the cable or nick the shield or worse, cause a short with it. Popular nylon 'Cable Ties' or 'Zip Ties' are excellent for using to attach coax to pipes, other wires, or tied downs made for them. Just don't cinch the tie down too tight, you don't want to crush your coax. For the perfectionist, you can get nylon 'Feed-throughs' to dress up any holes you drill in exterior walls, and plastic wall plates for the inside wall.

Putting it All Together
Let's start with the antenna/mast installation completed, you have connected the coax to the antenna, using a weather boot and silicone grease to seal the connection. Put an expansion loop (remember! 4"radius) at on the mast at the antenna end, and run the coax down as in any installation. Now, you have to get to the radio. In all cases, make a 'Drip Loop' wherever the coax enters the building. Imagine rain or moisture flowing down the outside of the coax. Where the coax enters the building, go beyond the point of entry, and make a 4"loop in the coax, so that the coax is exiting the wall in a downward position. Water getting in the building on your fault is undesirable.

Your installation may follow any one of these paths:

Attic (Truly Not My Favorite)
Put the coax into the attic through a vent under the eaves, or through a 3/8" hole. Once in the attic all that is left is to fish the wire down to desired location. Getting the coax down into a hollow wall is beyond the scope of this file, but I can pass on a tip, If there is a closet in the same or adjoining room, run the coax down through the ceiling in the closet, and down the corner in the closet, and through the interior wall.

Through Exterior Wall
While easy, this may be unsightly. Simply Drill a 3/8" hole in the wall, avoiding (!) any electrical wiring or plumbing that may exist. The best way to do this is to drill from the inside to out. Drill jjjjjjjustthrough the sheetrock or paneling, and STOP. Poke a screwdriver into the hole, and feel around for anything you may damage before proceeding. This also gives you the opportunity to shove aside any insulation in the wall, making feeding the coax through the wall easier. Put the nylon feedthrough on the coax, and poke it in. Feeding the coax from the outside my not be easy. TIP: go inside, and poke a piece of thin, stiff wire to the outside, seeing daylight through the hole helps. Strip 4"or so of insulation form the coax, and tape it to the wire to pull it through. Professional 18" drill bits used in CATV have a tiny hole in the valley of the working end, you leave the drill bit in the hole, then strip off 6" of insulation, leaving 6" of center conductor to put in the drill bit and wrap around it and use it to pull the coax through the wall. Put a wall plate over the coax, install the connector and you're done. TIP 2: Don't drill directly under a window, it will look very ugly on the outside, the window half-framed by black coax. Go directly underneath the left or right side of the window frame. Follow the already existing vertical lines on the exterior of the building, drain pipes, corner siding, or behind shrubbery help hide the coax.

Underneath the House or "got any clothes you don't care for?"
Using the same guidelines for exterior wall installation, run the coax from the roof to the basement or crawl space, entering though a vent or hole for the coax. Now it gets difficult, but will allow you to install the coax to a location away from an exterior wall . You drill a hole through the floor, and feed the coax up from the basement or crawl space. TIP 1: Run the coax from the antenna to the crawl space, using a vent or hole nearest to the trapdoor where you access the crawlspace. Then poke the coax into the crawlspace, and cut it there. This will be a splice point, and may be a good location to put in a ground block. Then go inside, drill down into the crawlspace, and feed enough coax you estimate will reach your splice point. TIP 2: Be careful with the drill, along with the Electrical/Plumbing situation above, you may take out several feet of carpet stitches when attempting to drill through the carpet. Cut an 'X' in the carpet, put the drill bit through the carpet and drill SLOWLY. Once you have the coax fed, all that's left is to crawl under the house and retrieve it, and bring it to the splice point. Another advantage to this method is that it allows you to keep several feet of coax under the floor, letting you move the scanner around a bit.

Got A Prewired House?
Many newer homes are prewired with coax for CATV or antenna use. Intercepting and utilizing the existing coax for your installation can save you a lot of work, and be most pleasing to the eye. If you have a spare prewired TV jack, in your monitoring location (or in an adjoining room, on the same wall...) you may want to use it for your scanner. Be aware that older homes may be prewired with smaller RG59 coax, and may not be of use for monitoring 900+ MHz. You need to find where the other end of the coax is, and splice into it. It may be in any location in the building, commonly near the utility entry point, or in the attic.