What Coax would you use?

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chazcarly

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If i was to put an antenna on the top of a telephone pole in my yard that has a area light on it, and then run underground to my house and to my scanner what coax would you use? The total run would be about 200'.
I was going to use a Diamond Discone antenna.
Any other suggestions would be appreciated.

Thanks
Matt
 

mmckenna

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Depends on frequencies you want to focus on.
The lower the frequency, the less expensive the coax you can get away with.
If you want performance on 700-800MHz then it's going to cost you.

AT 156MHz:
LMR-400 will lose about 3dB, or half the signal the antenna receives.
LMR-600 " " " 2dB.
1/2" heliax " " " 1.67dB
7/8" heliax " " " 0.9dB

At 850MHz:
LMR-400 will lose about 7.5dB
LMR-600 " " " 4.8dB
1/2" Heliax " " " 4dB
7/8" Heliax " " " 2.3dB

While they do make some "direct bury" cables, this alone isn't enough. You can bury these cables in a trench, but gophers can get it. They'll chew on the jacket and eventually the water displacement gel gets out and the water gets in.
Putting it in conduit would be a real good idea. Since you have to trench anyway, tossing in some pipe won't add much cost, plus it'll protect the cable from rodents and rocky soil.

If you are going to be listening mostly to VHF, then you could get away with something like LMR-400, but if you want good UHF and 700-800MHz coverage, you are really going to have to go with a bigger cable. And that gets expensive.

You could put a preamp out at the antenna and feed it power from your home. The pre-amp will boost the received signal and help overcome the losses. However, you do need to be careful with a preamp as they'll amplify everything in their passband and that can include things you don't want, like cellular, high power paging transmitter, a strong nearby FM station, etc.

You might want to consider keeping the antenna closer to your home and giving up some altitude.
 

FKimble

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Well, even LMR400 would have over a 3db loss at VHF freqs. Higher freqs would have even higher loss on a 200 ft run. Coax works better when it is mostly vertical. The area light on the pole would also concern me. First safety and second noise could be picked up from the light. If you could put the antenna up next to the house near the area where the coax will come in, it will help your signal even if it is just high enough to clear the roof line.

Frank
 

chazcarly

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Thanks,
I was going to put it in plastic conduit....as far as what freq. I listen to everything LOL.,
Here in NJ the police and fire are all over the place so its hard to lock in to a tight freq.
I would love to put it on the house but wife frowns on that idea. Have it in the attic now but want to get it out side.
 

jonwienke

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The light pole mount is a bad idea.

As mentioned, the proposed coax is too long to be practical unless you use some really expensive cable. LMR600 is over $100 for 50 feet, so you'd be spending over $400 just on coax. The Heliax is even more expensive.

Never run antenna cables next to AC power cables. The light fixture probably generates some amount of RF interference, which will get picked up by the antenna being next to the light. The RF will feed down the AC power cable and be inductively coupled to the coax if they are close together for any significant length. Plus, the current draw of the light will induce a 60Hz voltage in the coax when they are near each other. This can cause its own flavor of interference, damage the sensitive input transistors in your scanner, or even cause a shock hazard in extreme situations.

The best option is to put it on a pole or mast next to the house near the room where the scanner will be set up, to get the greatest antenna height from the least amount of coax.
 

jcop225

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Coax works better when it is mostly vertical. Frank
Please elaborate. As long as the dimensions of the dielectric is maintained I don't see why the orientation of the coax matters.

Never run antenna cables next to AC power cables. The light fixture probably generates some amount of RF interference, which will get picked up by the antenna being next to the light. The RF will feed down the AC power cable and be inductively coupled to the coax if they are close together for any significant length. Plus, the current draw of the light will induce a 60Hz voltage in the coax when they are near each other. This can cause its own flavor of interference, damage the sensitive input transistors in your scanner, or even cause a shock hazard in extreme situations.
R56 specifies minimum 2in. separation between RF and AC power cables. The antenna picking up interference from electronics in the light would be much more of a concern than any electrical safety issues.

There are plenty of towers with beacons on them so the two can cohab with the correct attention to detail.
 

n5ims

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There are plenty of towers with beacons on them so the two can cohab with the correct attention to detail.
True, many towers have beacons on them and often there are platforms where equipment can be mounted high on the tower to reduce coax loss, since instead of running the full height of the tower, it's only a few feet down to the equipment platform. These platforms require power for the equipment and air conditioner units to keep the equipment cool in the heat of summer.

The "attention to detail" is generally the coax runs are on one side of the tower while the power lines are inside of metal conduit on the other side of the tower so they're as far apart as is practical. This metal conduit also helps isolate the power lines from lightning and gives a larger ground path for the lengthy runs. This metal conduit is attached to the tower every ten feet or so to help keep the ground potential as close to possible to the same level and is securely connected to the tower ground system once it has reached ground level.

On insulated towers (such as AM broadcast towers) where the tower is used as the radiator, the power lines are not directly connected, but go through some strange looking transformers. Many are "ring transformers" that are two rings that intertwine where the power from the mains are on one ring and the power feeding the tower lights are on the other ring. Often there are two closely spaced bars that allow lightning to bypass the transformer and go directly to ground by jumping the small gap between the two bars (generally with balls on the end to maximize the area while minimizing the gap). A picture of one is attached.
 

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plughie

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If everything you listen to is within 1-2 miles from home and high power (like most emergency services), you can probably use RG-8 at 200 feet. Expect massive losses in the cable though. The light probably won't be too horrible for interference if it's incandescent. If it's fluorescent, HID, or LED, expect a LOT of noise.
Here's a site that has signal loss for various cable types: Coax Attenuation Chart
And here's how much of the signal is lost per dB: Losses & Gains per dB - Fleeman, Anderson & Bird, Corp.

Like the others above, I recommend going with a shorter cable run to increase your signal reception, and use the heaviest cable you can afford.
 

RFI-EMI-GUY

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Electrons go down hill faster.

Only works on RX antennas though.
On TX, you have to put a big amplifier to push all those electrons up the cable to the antenna.
It is alternating current, so those electrons have to make a round trip anyway.

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FKimble

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Ref my comment about vertical coax: When coax is running vertical, you are gaining height, hence better signal(usually). When coax is running horizontal, you are losing signal due to coax length. Better coax can help reduce the loss some.

Frank
 

jwt873

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If everything you listen to is within 1-2 miles from home (like most emergency services), you can probably use RG-8 at 200 feet.
I agree.. -3dB, -6dB or even 12dB really isn't really a big loss. It's only a few S units. The loss wouldn't be noticed if you're only scanning local government and business services.

My concern would be the power pole..

Do you own it or is it owned by the power company? If it's owned by the power company, you'll probably want to get their permission before you add anything to it.

FWIW, I live in the country and have a pole with a yard light on it. The power lines come from the road to the pole and then split going to my shop and to my house. But, the local power company owns the pole. I can't put anything on it.

Could you not just put up a mast on your house? That would probably be the easiest thing to do.
 

Rred

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"I don't see why the orientation of the coax matters."
The orientation doesn't matter. However, the installation does. If a cable lies flat, the weight is fairly evenly supported by the ground. When a cable goes vertical, it stretches under its own weight. That pulls the outer jacket "tighter" and pinches the insulating layer thinner, and that distorts all the properties of the cable. In order to properly suspend a vertical coax run, it needs to be tied off without being pinched or stressed every # many feet. There are wire mesh sleeves, similar to a "Chinese finger trap" that are used to do this. They ensure a wide grip on the cable and the least distortion to the insulating layer. And if that insulation is foam rather than solid--it is easily compressed and damaged.

After five years without proper support, even the best coax will test out very different from what it originally was.
 

n0jy

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Given the losses of the coax run, could you achieve similar or better performance by putting the antenna closer to the radio albeit perhaps not as high? That would reduce the cost of coax as well.

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bharvey2

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Electrons go down hill faster.

Only works on RX antennas though.
On TX, you have to put a big amplifier to push all those electrons up the cable to the antenna.
Good grief! Just spray the coax with electron lube!
 

lmrtek

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Just buy some solid copper center conductor burial rg6 and use a mast mounted preamp
 

captainmax1

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Can you install a switch to turn the light off when you are going to use radio equipment or is the light on community owned property. I would use the 7/8 wire if it was going to be 100' or more. Putting the discone on a mast closer to the house and using 50' of LMR400 might be a better deal as stated previously. Don't skimp on cable. I use and get great results with discone antennas. They are great for scanners and UHF/VHF Ham Tranceivers.
 

allend

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If i was to put an antenna on the top of a telephone pole in my yard that has a area light on it, and then run underground to my house and to my scanner what coax would you use? The total run would be about 200'.
I was going to use a Diamond Discone antenna.
Any other suggestions would be appreciated.

Thanks
Matt
Honestly I would never run 200 ft of coax or LMR. Just not a good idea. Between the 200 ft of coax and connector the loss is not going to go well. I think you are going to be dis-appointed and all of the hardwork and the time and money spent you will scrap the project and then re think the idea.

Just put up a 25 to 30 ft mast or pole and use a Diamond D3000N Disconne antenna on your roof or next to your shack and run either 50 feet of RG-6 coax or 50 to 100 feet of LMR 50 ohm feed wire.

You will get minimal to no loss and the disconne antenna is going to give you unity gain and you will have 25-1300 mhz receive for your radios or scanners.

Good Luck. Keep it simple. Antenna placement and running feed lines sometimes can be a science project. Plus Antenna placement is a huge hurdle. Don't rush and do some testing first to make sure you get the antenna placement at your home exactly right.

Good Luck
 

chazcarly

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Well thanks for all the input guys, a lot of good information !!
The light pole is owned by the electric company, I never thought about that.
As far as putting a mast on the house its not going to fly with the wife...LOL
and putting a pole next to the house wont work either.... that's why i was thinking about the telephone pole..
I have the Diamond in the Attic right now but this summer we put a metal roof on the house and the reception went in the ****ter.
Soooo that is my quest.....
What about in a tree ?? I have a very tall oaks about 30 feet from the house.They are over 60 feet high.
so i still would be at 150'.
Ideas ?

Thanks
Matt
 

Delta33

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MAKE the Wifey understand Or ...

But its far simpler just to mount the antenna on the House and call it a day ! ;)
 
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