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Coax Cable and Connectors For general discussion of all things pertaining to coax cable, wave guide or any other medium for passing RF energy. This includes connectors, weather proofing and grounding.

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Old 12-12-2013, 1:29 PM
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Default Two feed lines

Would adding a second balun and having 2 feed lines coming off a scantenna-2 be better than using a splitter? Would there be much difference in the signal? Only running 2 scanners and gonna replace old rg-6 with new rg-6 anyways on account of squirrel.. Setup as of now is 100ft rg-6 to splitter then 10ft each to scanner.
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Old 12-12-2013, 2:39 PM
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Generally no. If the antenna was designed to use a 300 to 75 ohm matching transformer then its probably around 300 ohms at the feedpoint. Adding a second balun and coax run would load the feedpoint down to around 150 ohms, which would incur additional loss above the 3dB loss from simply splitting the signal.
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Would adding a second balun and having 2 feed lines coming off a scantenna-2 be better than using a splitter? Would there be much difference in the signal? Only running 2 scanners and gonna replace old rg-6 with new rg-6 anyways on account of squirrel.. Setup as of now is 100ft rg-6 to splitter then 10ft each to scanner.
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Old 12-12-2013, 4:16 PM
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Generally no. If the antenna was designed to use a 300 to 75 ohm matching transformer then its probably around 300 ohms at the feedpoint. Adding a second balun and coax run would load the feedpoint down to around 150 ohms, which would incur additional loss above the 3dB loss from simply splitting the signal.
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Thanks for the info, I wasn't sure and know their is smarter people on here that knows more than I do.. Thanks again...
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Old 12-12-2013, 5:18 PM
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You 'may' be able to improve your antenna's performance by the following.

'System noise figure' is pretty much determined by the first stage in the system.
That first stage would be your coax and the loss will add directly to your noise figure.

So essentially, if you had a perfect receiver with a 0 dB noise figure, fed by coax with 9 dB of loss, your overall system noise figure would be greater than 9 dB. NOT very good.

Refer to this calculator. Cascaded Noise Figure Calculator

And this old post of mine.
Splitter, Amplifier, & coupler Noise figure

Assume that the first 'stage' in your system is your coax and enter it into the calculator as a negative number.

One problem many people have is using a low quality amplifier with too much gain.
That will increase the probability of overload and other problems.

It you add a low noise preamp right at the base of the antenna that is equal to the loss of your feedline (plus about 3 dB) you 'should' see a dramatic improvement.
That is assuming that you have no very strong signals nearby.

I run eight antennas. Five ST2 antennas, and three commercial antennas. All but one of them has a preamp right at the base of the antenna and they're all perfectly stable.
I have one antenna without a preamp for two reasons.
1. If I want to listen to MilAir, those with preamps have too many SatCom signals in the 200-300 MHz range.
2. I need something to use during power outages that requires no power supply.

If you listen to my feed, you'll see how an ST2 with a good preamp works.
It's feeding 32 scanners at the same time.

Rich
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Old 12-12-2013, 8:35 PM
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Originally Posted by rbm View Post
You 'may' be able to improve your antenna's performance by the following.

'System noise figure' is pretty much determined by the first stage in the system.
That first stage would be your coax and the loss will add directly to your noise figure.

So essentially, if you had a perfect receiver with a 0 dB noise figure, fed by coax with 9 dB of loss, your overall system noise figure would be greater than 9 dB. NOT very good.

Refer to this calculator. Cascaded Noise Figure Calculator

And this old post of mine.
Splitter, Amplifier, & coupler Noise figure

Assume that the first 'stage' in your system is your coax and enter it into the calculator as a negative number.

One problem many people have is using a low quality amplifier with too much gain.
That will increase the probability of overload and other problems.

It you add a low noise preamp right at the base of the antenna that is equal to the loss of your feedline (plus about 3 dB) you 'should' see a dramatic improvement.
That is assuming that you have no very strong signals nearby.

I run eight antennas. Five ST2 antennas, and three commercial antennas. All but one of them has a preamp right at the base of the antenna and they're all perfectly stable.
I have one antenna without a preamp for two reasons.
1. If I want to listen to MilAir, those with preamps have too many SatCom signals in the 200-300 MHz range.
2. I need something to use during power outages that requires no power supply.

If you listen to my feed, you'll see how an ST2 with a good preamp works.
It's feeding 32 scanners at the same time.

Rich
Thanks...
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Old 12-13-2013, 4:11 PM
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...which would incur additional loss above the 3dB loss from simply splitting the signal.
prcguy
Also, the 3 db loss is almost completely unnoticeable on FM signals. Once a signal is in saturation, it doesn't matter at all. And in weak signal environments, 3 db is the difference between a noisy signal, and a slightly noisier signal. Use a splitter and ignore the loss.
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Old 12-14-2013, 12:40 AM
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Also, the 3 db loss is almost completely unnoticeable on FM signals. Once a signal is in saturation, it doesn't matter at all. And in weak signal environments, 3 db is the difference between a noisy signal, and a slightly noisier signal. Use a splitter and ignore the loss.
Gonna use the splitter, right know I am using this one not sure if there us a better one.. New 2 Way Antronix Cable TV Splitter CMC2002H High Performance Coax 5 1000MHz | eBay
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