Cable Run for Commercial Building

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Gilligan

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I'm considering installing a mobile antenna on a roof hatch on a commercial building. I have tested it and the hatch works great as a ground plane. The building is four stories high and I believe the cable run would be approximately 100 feet. I'm primarily using the antenna for scanning 450-470 MHz. What would be the best kind of cable to run for this to avoid as much loss as possible? If it is expensive, is the next best option going to make much difference? I just want to make sure that I'm still going to have a signal after running 100 ft... Also, I have one of those GRE antenna amplifiers -- would it be recommended in this situation?
 

radioman2001

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First go for some good coax. RG-213, 9913 or equivelant( BTW 9913 is fine for RX only systems, I just wouldn't use for a duplex repeater), next use a good hi-gain mobile antenna. How far or how weak are the signals you are attempting to get as most UHF is repeated so you may not need an amp, and if you do need one you don't need to go crazy with an expensive one, a TV amp from RS will suffice. I use one at home and have it split 4 ways and don't notice any degradation of signal.
 

mass-man

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Is there a ham store near you? I would explain to them what you want to do. Buy a roll of RG6X with good connectors and go up on the roof and give it a try. You don't have to unroll it and thread it down the building. Take your scanner, antenna, cable, put it all together and give a listen. If you find there are things you can't hear, take the cable back, unrolled and buy the next more expensive. I would skip the amp unless you really need it. It will add noise to the signals, either strong or weak.
Do not use connector adapters, they increase signal loss.
 
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Gilligan

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I have a gain antenna for 450-470 and will be using this for receive only. I definitely appreciate the help as these answers have been very informative. Any idea on how to ground this thing if I can't bring a ground line outside the building? Would there possibly be anything on the rooftop I could ground it to instead? There is already a tv satellite dish installed up there nearby...
 

Gilligan

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What about this? Would this probably work? I'm mainly trying to listen to LTR/Passport repeaters from nearby counties. I also have a 450-470 beam antenna that I may try. I'm noticing that 100ft of cable can cost well over $100, whereas this option is about $45:

100ft RG8x Coax BNC Male to Male 50 ohm Antenna Cable

RG-8X male to male 50 ohm shielded cable with BNC plugs on both ends. All the connections inside are soldered and the cable is made of copper conductors. RG8X coax is a step up from standard RG-58 coaxial and is recommended for high-powered applications or users who simply want the best coax possible.

Specifications:
High Quality RG-8X Coax antenna cable w/ braided copper shielding
(2) BNC male plug
Great as jumpers to an antenna tuner, switch, meter or your main antenna
50Ω Low-loss RG8x-mini
Fully molded
Nickel-plated connectors
Length: 100 ft
 

902

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What about this? Would this probably work? I'm mainly trying to listen to LTR/Passport repeaters from nearby counties. I also have a 450-470 beam antenna that I may try. I'm noticing that 100ft of cable can cost well over $100, whereas this option is about $45:

100ft RG8x Coax BNC Male to Male 50 ohm Antenna Cable

RG-8X male to male 50 ohm shielded cable with BNC plugs on both ends. All the connections inside are soldered and the cable is made of copper conductors. RG8X coax is a step up from standard RG-58 coaxial and is recommended for high-powered applications or users who simply want the best coax possible.

Specifications:
High Quality RG-8X Coax antenna cable w/ braided copper shielding
(2) BNC male plug
Great as jumpers to an antenna tuner, switch, meter or your main antenna
50Ω Low-loss RG8x-mini
Fully molded
Nickel-plated connectors
Length: 100 ft

What you do is ultimately up to you, but I haven't seen anyone explain the concept of "loss" in a cable yet. At some point, the smaller the diameter of cable you use - and to a great extent, the quality and characteristics of the cable you use, the more you may lose in moving the signal from the antenna down to the scanner. You may want to budget a little more for the cable and antenna so you get the most out of your reception.

Another caveat - a preamp might work fine, and if it does, will help offset the loss in using a cable with less-desirable characteristics. HOWEVER, it may also introduce noise, desensitization, and mixing products into your system. The best practice is to build it to use without the preamp, then you can try it if you feel you need it - but won't need to depend on it if you prove that it introduces problems.

Good luck!
 
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You did specify that this we a commercial structure therein brings up other issues regarding the suitability of the cable and how it's routed. The building inspector and the Fire Marshall will have the last word on what and how it will be installed, don't think they will approve a mag mount antenna on the roof hatch.
 

Gilligan

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You did specify that this we a commercial structure therein brings up other issues regarding the suitability of the cable and how it's routed. The building inspector and the Fire Marshall will have the last word on what and how it will be installed, don't think they will approve a mag mount antenna on the roof hatch.
Is it considered unsafe?
 

mmckenna

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Is it considered unsafe?

No, it's done all the time, you just need to use the right cable.

Depending on -where- you run the cable, you will need a specific type.
The standard outdoor cable usually isn't suitable for in-buildng use due to flame propagation and smoke issues. If there was a fire in the building, your new cable could be a source of issues. The cable itself can burn and help spread the fire. The burning cable on it's own can introduce all kinds of toxic gases into the atmosphere.

Where you run the cable is key:

If it's running between floors, you will need to use (at minimum) a riser rated cable. These will usually be marked with "CMR" on the jacket somewhere. This means its a communications cable, riser rated.

If the cable is run in any air handling spaces, such as in a drop ceiling that is used as part of the air return system, then you will need to use a plenum rated cable. These will be marked with CMP on the jacket.

These riser and plenum rated cables will usually be different than what you run outdoors. They'll likely cost more, too.

At absolute minimum, I'd recommend running a riser rated coax cable. You can find this fairly easily in the RG-6 rated cables as they are often used for cable TV distribution inside buildings. Finding Plenum rated will be a bit harder, as in not likely at your local hardware store, but it's out there.
 

mmckenna

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Is it considered unsafe?

Oh, and grounding....

You are sticking a piece of metal up in the air, and then giving it a path down into the building. Lightning may or may not be a concern, but unless it is your building, I'd recommend addressing this.

Make sure the roof hatch is grounded. Don't rely on the hinges. A ground braid would be a good idea.

Ground the outer shield of the coax cable to the building ground or building frame.

Install a Polyphaser or similar type protector near the cable entrance. Ground to the building ground or frame.
 

Gilligan

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Thanks to everyone for all of the help. I'm definitely thinking that this is not worthwhile with lightning liabilities, etc, however I have a lot of useful information now. Thanks again!
 
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