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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 11-14-2017, 6:50 PM
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Default Cable advice

Need a little advice here, still very much new to this stuff. After researching a good antenna and cable suggestion. I am going with a 50ft LMR400 low loss cable from a OmniX antenna to my scanner. I realize this cable is quite stiff and will also need to run about a 10ft patch cable from the LMR400 to the scanner.

I am looking for a 10ft BNC Male to BNC Female patch cable. Was looking at the LMR 240 Ultra Flex cable for that based on my research.

Questions I have:

Does this setup sound reasonable?

Any other suggestions for a 10ft cable I should consider that is not going to mess my signal up?

Where are people buying these kind of cables? I cannot seem to find a reasonably priced site online.
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Old 11-14-2017, 8:17 PM
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For what frequencies? 50' of LMR400 is around 2 dB loss for the 800 mHz frequencies. Not killer by any means, but if what you're listening to is far away you could miss stuff. LMR600 or Heliax would be more ideal, but costs more. Any specific reason you need a 10' patch cable? Depending on the radio and connectors I use either a foot or 18" of RG-58A/U.

While they can be pricey, this eBay store has custom made cables. If you don't see what you want, ask, and they'll make it for you. MPD Digital Custom US Made Cables | eBay Stores
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Old 11-14-2017, 8:24 PM
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I primarily went with this antenna because it is tuned to 118-137, 148-175 & 225-900 MHz. Most of the stuff I listen to is 118-137, 148-175. But I will monitor HAM and some other stuff above 225.

10' cable or possibly less. I might come up just a tad short on my 50 ft run. If I can use a shorter cable I will. Thanks for the RG-58 suggestion and I will check that store out.
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Old 11-15-2017, 4:06 AM
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Quote:
Originally Posted by deltaleader View Post
... Most of the stuff I listen to is 118-137, 148-175. But I will monitor HAM and some other stuff above 225....
It's overkill going for a LMR400 coax. Only if you intend to transmit should you consider that coax.
At 200MHz the LMR400 attenuate 0,8dB and RG6 1,4dB. It is a 0,6dB difference but the difference in cost and easy of installation are tremendous.

The money you save could be used to buy a good amplifier and a FM trap filter that will give you better reception than any coax can do.
The amplifier will increase the bandwidth of the antenna and also give a constant impedance to the coax and scanner that will eliminate any SWR that will ruin reception.
If the amplifier are of good quality it will also lower the noise floor of your scanner so you will be able to hear signals that are below what the scanner itself can receive.

/Ubbe
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Old 11-15-2017, 10:43 AM
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I have 11 scanners running in my house for listening to many different agencies from public safety to marine. A friend of mine is owner of a communication co. When i met this friend for the first time 30 years ago his motto was your antenna and coax are the most important part of the systems...

I have tried to use many different types of coax from RG-58 to RG 8 mini and regular, LMR-400, RG-6 and RG-11. I really liked the RG-6, and my brother worked for a cable co. and he'd cut me different size pieces all the time.

My friend is like ditch that 75 oam cable and try some 1/2" cable...80' run did it on one of my antennas, and what a difference. I went back and changed another antenna out the was like 70' and again awesome.
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Old 11-15-2017, 11:19 AM
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Quote:
Originally Posted by Ubbe View Post
It's overkill going for a LMR400 coax. Only if you intend to transmit should you consider that coax.
At 200MHz the LMR400 attenuate 0,8dB and RG6 1,4dB. It is a 0,6dB difference but the difference in cost and easy of installation are tremendous.

The money you save could be used to buy a good amplifier and a FM trap filter that will give you better reception than any coax can do.
The amplifier will increase the bandwidth of the antenna and also give a constant impedance to the coax and scanner that will eliminate any SWR that will ruin reception.
If the amplifier are of good quality it will also lower the noise floor of your scanner so you will be able to hear signals that are below what the scanner itself can receive.

/Ubbe
Not trying to be a nit picker here, but your selection of words about the SWR on receive will ruin reception just doesn't cut the mustard. Receiver transmission line is much more forgiving than in transmit.

The other point is since when does an in line amplifier lower the noise floor? Any amplifier you put in line to bring up signals that are low in strength will also raise the noise floor of all signals. That's just the physics of the way it works. How much the noise floor raises will depend on the quality of the amplifier. Some are decent and others are terrible on raising the noise floor. Cost is a factor here in most cases. The better low noise amps will just cost more. But you can get junk and still pay the higher cost. Need to pay attention to the amplifier specs.

Your giving facts here that are just not correct. Lets not send a new comer to the group here down the wrong road.
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Old 11-15-2017, 11:53 AM
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Thanks for the input all. The reason I went with LMR400 was based on reading various forums, cost and the fact I will intend to transmit at some point in the near future. HAM radio license was one thing I was considering in the near future.

I am not sure about amps and traps right now. The first thing for me to do is get this all going and see how it performs. Then build my way up.
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Old 11-15-2017, 12:38 PM
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For the short patch cable, personally I would go for either RG8x or LMR240 rather than RG58.

You might also consider a patch cable with BNC males on both ends (probably less expensive than a custom cable) and then use a BNC female adapter to transition to whatever connector is on the LMR400 cable.

-John AC4JK
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Old 11-15-2017, 2:58 PM
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Originally Posted by jim202 View Post
Not trying to be a nit picker here, but your selection of words about the SWR on receive will ruin reception just doesn't cut the mustard. Receiver transmission line is much more forgiving than in transmit.
It doesn't matter in which direction the signal goes with regards to SWR. The signal in the coax are reflecting back to it's source and will at certain points in the coax cancel out the signal more or less depending of the magnitude of the SWR. If the signal goes below the noise floor it is lost forever.

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Originally Posted by jim202 View Post
The other point is since when does an in line amplifier lower the noise floor?
Lets says the scanners first amplifier stage have a noise figure of 3dB. Any signal that are not 3dB higher than the natural atmospheric noise floor will be masked by the scanners internal noise. Adding an amplifier that has 0,6dB internal noise and 10dB gain will raise both signal and noise floor 10dB and the scanners 3dB noise are taken out of the equation and you get a 2,4dB better sensitivity. Then add no coax attenuation and the constant impedans and you'll have a huge increase in reception. Anyone that has tried a good antenna amplifier can testify to this. Only drawback are that the scanner might be overloaded by any local strong signal and may need additional filtering to get rid of that interference.

But the OP wanted to transmit at a later stage with his coax and then his LMR400 suggestion seems relevant.

/Ubbe
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Old 11-15-2017, 4:23 PM
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Just another Pre-amp hater that has never figured out how a good Pre-amp/LNA needs to be set up and how well one works, even a wideband unit. So many people throw in the towel when there is not an immediate improvement. Most of the time if the Pre-amp/LNA does not improve things something is wrong with the implentation. If previous signals are washed out, this usually means the Pre-amp/LNA is over driven or there are intermods due to strong signals from local FM Broadcast or other source. Many Pre-amp/LNA configurations need to be appropriately balanced, filtered and messaged as needed. Also you need to be very worried about very low noise figure devices that are under $75, some may have decent noise figures, but most junk from Asia under $15 will not perform to spec.

A little ingenuity goes a LONG way if you are patient. Ask me how I know.

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Old 11-15-2017, 4:31 PM
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As long as you're not transmitting on it, RG6 would be good overall choice. Inexpensive, easy to work with, flexible, low loss.

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Old 11-15-2017, 7:46 PM
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I agree with Ubbe - LMR400 is overkill for just 50'. I personally prefer LMR240 and then you wouldn't need the pigtails. But really it's what you want. If you want to pay the extra for LMR400 and that's what you want go for it. As far as where to buy cable - my first choice is The Antenna Farm The Antenna Farm, Your two way radio source. My second choice is MPD Digital on Ebay. I have used both and never a problem. MPD is usually more expensive though. Good luck.
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Old 11-15-2017, 7:50 PM
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If you have an antenna that presents a 50 ohm impedance over the frequency range you want to operate you can choose a low loss 50 ohm cable like LMR400 or LMR600 and get very predictable results. No funny business and unknown varying loss across the bands due to a mismatch using 75 ohm coax, etc.

The main problem with recommending a preamp is unless you carefully measure what comes off your antenna with a spectrum analyzer first and size the preamp for gain, NF and especially IP1 and IP3, you will never know how it will work until its installed.

For many people it will be trouble due to the preamp getting blitzed, creating lots of IMD and reception will be worse with the preamp in that case. Then they will have to choose to spend even more money on a higher level preamp if its even available, or scrap the whole thing and get low loss coax.

I have the tools, equipment and knowledge to measure receive levels before choosing a preamp, but most people don't. I would rather recommend a known solution that will be an improvement like going with good low loss 50 ohm coax or a better antenna or both.
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Quote:
Originally Posted by JamesO View Post
Just another Pre-amp hater that has never figured out how a good Pre-amp/LNA needs to be set up and how well one works, even a wideband unit. So many people throw in the towel when there is not an immediate improvement. Most of the time if the Pre-amp/LNA does not improve things something is wrong with the implentation. If previous signals are washed out, this usually means the Pre-amp/LNA is over driven or there are intermods due to strong signals from local FM Broadcast or other source. Many Pre-amp/LNA configurations need to be appropriately balanced, filtered and messaged as needed. Also you need to be very worried about very low noise figure devices that are under $75, some may have decent noise figures, but most junk from Asia under $15 will not perform to spec.

A little ingenuity goes a LONG way if you are patient. Ask me how I know.

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Old 11-15-2017, 8:23 PM
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Quote:
Originally Posted by deltaleader View Post
Need a little advice here, still very much new to this stuff. After researching a good antenna and cable suggestion. I am going with a 50ft LMR400 low loss cable from a OmniX antenna to my scanner. I realize this cable is quite stiff and will also need to run about a 10ft patch cable from the LMR400 to the scanner.

I am looking for a 10ft BNC Male to BNC Female patch cable. Was looking at the LMR 240 Ultra Flex cable for that based on my research.

Questions I have:

Does this setup sound reasonable?

Any other suggestions for a 10ft cable I should consider that is not going to mess my signal up?

Where are people buying these kind of cables? I cannot seem to find a reasonably priced site online.
For what it's worth and all due respect to the above posters, I swear by Times LMR240 for all my feedlines and patches-my patch from my antenna switch in the living room runs 32' to my SX-88 in the bedroom...no loss. Last time I bought runs of LMR240m I went with the Ultra-Flex when I normally go for the hardline. I don't like the Ultra-Flex mainly because I feel its jacket is too soft and cheap. Next time I make it to HRO in Oakland I intend to get the hardline. Very strong stuff and pretty easy to work with for hardline. I still have the hardline from several years ago feeding my scanner's D130J. Still like new and reliable through all the salt and weather here. Check HRO-they're pretty reasonable.
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Old 11-15-2017, 8:54 PM
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I also have the tools, equipment and knowledge to determine what my spectrum looks like. I also can use some modeling tools to predict with a reasonable level of accuracy what may occur with FM and TV Broadcast.

I have also vetted a number of Pre-amps and found a quality product at a reasonable price point that in some instances would be cheaper than an antenna and coax upgrade so I put this out for anyone that would consider this as an option. But they need to listen and follow directions, cheap amplifiers are not the solution and most sites need an FM Broadcast filter.

As with any change in a receive path, often the first attempt may not be successful and addition effort and experimentation may be required.
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Old 11-16-2017, 6:59 PM
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rg8x is very flexible and a 10 ft jumper of it won't hurt much
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Old 11-16-2017, 7:57 PM
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LMR240 is the same size as RG-8X, has about 50% less loss and it only costs a little more.
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rg8x is very flexible and a 10 ft jumper of it won't hurt much
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Old 11-16-2017, 11:17 PM
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My second choice is MPD Digital on Ebay. I have used both and never a problem. MPD is usually more expensive though. Good luck.
MPD is expensive, but their quality is excellent.
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Old 11-17-2017, 6:22 PM
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Thanks all for the information. I got everything up a going today and am very happy with the quality I am hearing. No more static and unclear receives. Granted I am mostly monitoring my local area but the Omni-X antenna made a huge difference plus it is on the roof with a clear view of the skyline.

I did go with the 50ft LMR400. Found a shorter route through my attic which technically saves me from having to use a jumper, but the coax is stiff for my handheld. So I am going to use a 3ft. LMR 240 UF to ease up the tension.

I did end up using MPD which I think their web site routed me to https://usacoax.com/. I didn't go through ebay on that one.
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