Using TV cable for scanners?

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phillydjdan

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Forgive me if this has already been discussed. Tapatalk gave me zero search results. Can a person use regular TV coaxial cable to feed multiple scanners? What would the drawbacks be? You see tons of TV coax around and plenty of splitters for far less than communications grade stuff. What I would ideally like to to is split my discone to 6 or 8 scanners. I could use TV coax jumpers to connect the scanners via adapters at the ends. What are your thoughts?

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rbm

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If you're talking 'good' RG6 coax, I do it all the time.
Anything less isn't worth trying.

I have three rolls of it on hand now.
Two 1,000' rolls of solid copper center conductor and one 500' roll of dual RG6 with a messenger wire (used to power my antenna mounted pre-amps).

Use good quality compression connectors to make weatherproof connections and you won't have a problem.
I buy them 1,000 at a time. ;)
(PPC EX6XL PLUS RG6 Compression Connectors)

It works good for short runs or over longer runs with a low noise pre-amp right at the antenna to make up for any loss.

Rich

Edit: As I mentioned in another thread, I feed 32 scanners with one ST2 antenna.
One of those is my Broadcastify feed, at the icon above.

Here's a photo of a sample I put together for a friend to feed up to 16 scanners.
It works great for him.
But in strong signal areas, I would recommend a better amplifier.


 
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pinballwiz86

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Yes, you can use TV cable. No, you don't want to though.

I would get some better coax OP depending on the frequencies you listen to. Anything above VHF, you'll have high losses with that cheap TV cable. Especially if you're thinking of splitting it to 8 scanners?

Look at DX Engineering 400MAX Low-Loss 50-ohm Coaxial Cable Assemblies with some adapters.
 

n5ims

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Think about the frequencies (which is what drives coax loss - the higher the frequency, the higher the loss). TV from around 50 MHz to around 900 MHz. Scanners from around 50 MHz to around 900 MHz. Sounds like a pretty good match so whatever works well for one could easily work well for the other.

The typical TV coax was designed for use by the Cable-TV industry to provide a good, inexpensive way to transmit the signal from the pole to the TVs. Good performance over the TV frequency range was important. Since scanners also work using similar frequencies it's a good choice.

There are differences (75 ohm impedance for TV cable vs. 50 ohm for scanners for example) but bang for the buck will fall on the RG-6 side. For best performance, you can easily do better, but at a cost. RG-6 is easy to install and inexpensive. LMR-400 (or the much better LDF4-50A) is more difficult to install (it's very stiff) and will provide lower loss, but for at least double the cost.
 

ka3nxn

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RBM IS RIGHT!!! As long as it's not the cheap RG-59 the RG-6 is excellent for single or multiple scanners. Especially if it comes from a satellite TV provider. In the U.S satellite TV covers from approximately 950-2150MHz, so it covers 99% of the frequencies that most scanner listeners monitor. So there is no need to go out and purchase expensive bulky LMR-400 especially if you aren't going to be transmitting. This is a major misconception about 75ohm coax that you can't use it for radio. Have at it use the RG-6 if you have it available. Now the only other reason I would go out and purchase expensive coax is also if you are going to have a seriously long run i.e. more than several 100 feet.

Jaime-KA3NXN
 

jackj

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Draw up a block diagram of you station so you have a good picture of what you want. Next, list the lengths of coax you need to connect everything together. Add the lengths of coax from you antenna to your farthest scanner.

There are several good sites that list the attenuation of common coax cable per 100 feet. Add in the attenuation of any signal splitters you will use and you will have the signal loss you will need to deal with.

All scanners and most antennas are designed with an impedance of 50 ohm. Changes in impedance will cause a bump in impedance and that bump will cause some of the signal to be reflected back to its source increasing loss. Pick a transmission line for the longest run and stick with the same impedance for all other jumpers, amps and splitters.
 

phillydjdan

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My run would be about 50 feet or so. So as long as I use good quality RG6 I should be okay, right? I'm not trying to tune in very far stations with it, I just need to split it for multiple feed scanners. Is there any manufacturer or brand that is better?

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rbm

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I have to go out, but here's a quick visual before I do.

I fired up one of my USB dongles and RTL1090 & Virtual Radar Server to track some aircraft at 1090 MHz.

This is on the ST2 antenna that has 32 ports.

I only let it track for a few minutes because I'm running late. ;)

The furthest aircraft right now is around 75 miles out.

Typically if I let it run for a while I'll track aircraft out to around 100 nmi.

Rich

Edit: I should have mentioned that the RG6 run into the house is around 85'.
With a preamp at the antenna.


 

rbm

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My run would be about 50 feet or so. So as long as I use good quality RG6 I should be okay, right? I'm not trying to tune in very far stations with it, I just need to split it for multiple feed scanners. Is there any manufacturer or brand that is better?

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Try to find cable that is swept to 3 GHz. That's often the better stuff.
Something like this: (50ft is $13.79 w/free shipping)
You probably want to stay away from 'Quad shield' cable because that can give you additional problems when installing some connectors etc.

New RG6 3GHz Shielded Solid Copper Coaxial Coax Cable Custom Size DirecTV Dish | eBay

Edit:
The above cable comes with these connectors installed.

http://www.amazon.com/Thomas-Betts-...1403928073&sr=8-1&keywords=Belden+Snap+n+Seal

Although at higher frequencies, 'copper clad steel' center conductor is 'just about' as good RF-wise.

I use only solid copper because there are times I feed 12V on the feed line to power amplifiers.
The steel center conductor has far too much loss at DC.

Below, you can see approximately how much signal you'll lose when you feed multiple scanners.
Always figure on the high side of the numbers.
Each connector will also have a little loss 0.1-0.2 dB or so. (if installed correctly)

'Ball park' losses for splitters: (per port)

A 2-way splitter has around 4 dB loss
A 3-way splitter has around 7-8 dB loss
A 4-way splitter has around 9-11 dB loss
An 8-way splitter has around 13.5 dB loss

Rich

A couple more thoughts....
Some splitters will have different attenuation per port.
I have some 3-way splitters for example that have ............... -3.5dB , -7.5 dB , -7.5 db (per port)
That works well for me in some cases.
Be aware that there are good splitters and TERRIBLE splitters out there.
It's best to use respected name brand devices..
You may wonder why some 2-way splitters are $.99 and others are $7, that's why. ;)
And make sure the splitter is spec'd for the frequency range you care about.
 
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phillydjdan

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Thanks for the replies. I was thinking, I already have the 50 foot run of LMR 400, would it hurt to throw an adapter on the end of that and then use TV splitters and short (maybe 2 foot) jumpers from there? As it stands now I am using numerous SO239 T splitters with some LMR and some RG8 jumpers, and its very ugly. The problem is I dont have the dough to buy a multicoupler.
 

jackj

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If you can't afford to do the job with the proper equipment then it might be better to wait until you can. Regardless of what you decide to do, you will be spending 'some' money and if you have to go back and re-do the job then that money will have been wasted. It has been my experience that doing the job right the first time costs less in the long run.

LMR-400 is 50 ohm coax so using it with 75 ohm TV splitters will result in impedance bumps and increased loss. The loss will not be predictable as it will be caused by signal reflection and not transmission loss. SO239/PL259 connectors are not really good above about 100 MHz, the connectors themselves cause impedance bumps. Also T-type splitters will cause their own problems as they will effectively double-terminate the cable.
 

popnokick

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When I had satellite TV installed in my house they ran all new coax from the dish, and did not want to use the existing Cable TV coax and jacks that were all over the house. So I put a scanner antenna in the attic (OCFD) and connected it to a splitter/amp feeding the old CATV coax. Voila! A jack in nearly every room of the house where I can connect a scanner and take advantage of the antenna in the attic. Yes, I'm certain there is some loss but neither my radios nor my ears have noticed. I receive everything on all radios just as if they were directly connected in the attic.
 

gmclam

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Antenna cable or system

Not all cable is created equal. There is good and bad quality "scanner" cable just as there is good and bad quality "cable TV" cable.

You really have to look at your antenna and cable as a system; especially if driving multiple scanners. I am personally driving a fairly large number of scanners in various rooms from an outdoor antenna. I am using an LMR-400 clone (Air-802) for the downlead from a discone to my central distribution point; but from there it's quite a mix.

Since this is receive only I did not concern myself with the 75 ohm vs 50 ohm impedance difference. However, I did pay great attention to the LOSS of the cable I am using, at the highest frequency (typically 870MHz), over the length of the run (as much as 70 feet). I was able to provide different "tap levels" from my central distribution point so that the signal levels at the scanner ends of the cables were similar.

I used a discone as the antenna, but largely used cable TV equipment (although a low noise amplifier) for the system. I also have equipment to measure the levels along the cable paths. If you want to get in to designing a system, you can use good quality cable. But lots of people don't have equipment/etc to do the job or desire to get into it at that much complexity.
 

zz0468

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If you're going to use TV cable, just make sure it's good quality with a recognizable manufacturer name on it. I once bought some TV cable from Walmart or Target, or some such store for some actual TV wiring in the house. I put it all in, and nothing worked. It turned out that the cable was such poor quality, the copper plated steel center conductor had such a thin layer of copper on it so the loss was atrocious - like, 30 db per 10 feet of cable.

Don't cheap out on yourself when it comes to buying cable. get the best you can afford. If you have to cut corners somewhere, go cheap on the batteries for the kids toys - the house will be quieter so you can listen better.
 

phillydjdan

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Here's a question. If I found a metal box of appropriate size to do so, would it be better (for signal loss) to install several BNC and/or SO239 surface mount connectors and solder them all to one SO239 connector via solid wire? Would the metal enclosure help reduce loss? Is there any additional steps that I could take to cut down on loss? I have no problem pulling out the soldering iron if it would be pheasable to do so.
 

WA0CBW

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It is probably not a good idea to directly connect all the scanners together without some kind of isolation between each connection (think splitters or multi-couplers). Also remember that the signal coming in from the antenna is divided among all the scanners so the loss with 6 scanners means each scanner only gets 1/6 of the available signal.
BB
 

phillydjdan

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Well, they are all connected together via T splitters now, so how much worse could it really be? Anyone have any schematics or plans for a home made multi coupler? Whats all involved in building one?
 

zz0468

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Well, they are all connected together via T splitters now, so how much worse could it really be? Anyone have any schematics or plans for a home made multi coupler? Whats all involved in building one?
What frequencies do you expect the thing to work on?
 

737mech

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Multicoupler

Yes you do have the money for a multicoupler, search Ebay for electroline 8 way splitter like the eda2800 or eda2802. They are usually $20.
 
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