Coax: RG8UFoam, LMR400, LMR400Flex?

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robman50

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Hello,
I would like to get a coax that has the lowest loss possible for a 80 foot run from my scanner to my antenna.
I don't know what type of coax I should use but I was told that the LMR400Flex is for rotatable antennas? Since I am using a discone, that is not necessary.

Here are some of the choices.
Coax LMR400 Equivalent Cable 50 Ohm|LMR400 ( equivalent ) [CAB-LL400] : @ Radioworld Toronto
LMR400FLEX Cable Coax Strand Core (9913 Flex) - Durham Radio Sales and Service Canada
RG8UFOAM Heavy Duty Coax Cable - Durham Radio Sales and Service Canada
 

bharvey2

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I've used quite a bit of LMR400 and have been happy with it. It has less loss that RG8 Foam.
 

bharvey2

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LMR400Flex does bend more easily. But, if you're only going to route it once and leave it alone after that (and aren't using a rotator) I don't think you'd get much benefit from buying the flex version. In any case, you don't want to create a tight bend radius. I try to adhere to a bend no tighter that 10X the radius of the cable I'm using. A greater radius is even better in some instances. If you get too tight you can kink the cable and the center conductor can even migrate toward the shield over time.
 

robman50

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Here is another option.
http://www.amazon.ca/gp/product/B007ZQUW1O/ref=olp_product_details?ie=UTF8&me=
I can get it as cheap as $149 CDN.
The thing I don't understand is this, 'PL-259 Connectors are not recomended for use above 300Mhz (See N Male options).'
I like to do everything though. I've seen some stuff up on 400+ Mhz, so should I just use 'N'? What is an 'N' connecter anyway?
 
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bharvey2

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PL259 connectors are more lossy that N ones. I couldn't tell you by how much though. Although, I've seen some commercial radio designed for 400-500MHZ that have PL259/SO239 connectors factory installed and have used them myself without any obvious trouble. I've never done a side by side comparison though. Given your application, I think you'd be alright with PL259s.

Making 90 degree bends are fine. You just don't want them too sharp. When making those bends, think in terms of wrapping the cable 1/4 way around a large coffee can instead of folding the cable over the edge of a table. - I hope my description makes sense.
 

teufler

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Coax Loss Calculator
this is a line loss calculation page. Belden 9913 is almost as goodf as lmr 400, a couple of thenths greater loss, at 400 mhz for 80 feet. Not a big deal, you are not transmitting, pl259 will work on the antenna end, you will either scream at putting on a bnc plug or get an adapter pl259 to bnc. Belden 9913 bends more than lmr 400, hence much easier to work with. lmr 400 , is about $1.22 per foot, while belden 9913 is about $0.70 per foot. Both are double jacketed. Lmr 400 has a better jacket, stands up to weather, heat, cold, sun, coax cracking, but this will occur after 6 or 7 years.
 

cg

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LMR400 has a solid center conductor. The Flex has a stranded conductor.
That $2.60/foot price seems high. I just did a quick EBAY search and found 100' with no connectors for $150US shipped to Canada.
Wherever you buy it, be sure it is Times Microwave LMR coax and not "equivalent"

chris
 

cg

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Belden 9913 has air dielectric where LMR 400 has foam. That refers to what separates the center conductor from the shielding.
I have seen 9913 fill up with water due to a squirrel making a small hole through the outer jacket.

Brand name Times Microwave coax is all I use for my scanner antennas. LMR600 for 700/800MHz and LMR400 for VHF/UHF.


chris
 

robman50

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According to the store, here is what they said about the RG8UFoam. 'This is LMR400 equivalent' and '
The electrical losses are the same. The difference is the outer vinyl. LMR400flex has a higher quality softer vinyl.'
 

n5ims

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The thing I don't understand is this, 'PL-259 Connectors are not recomended for use above 300Mhz (See N Male options).'

One thing others haven't mentioned (something to remember when talking about RG-8 coax) is that RG-8X or Mini-8 coax (smaller diameter, about 1/4 - 1/3") is no where the same as standard RG-8 (about 1/2" diameter) in performance or loss numbers. RG-8X was designed for HF use and works well there, but has way too much loss for VHF or UHF use. While it may "work", it won't "work well" except for very short runs.

"N" connectors are a bit less lossy than the typical "UHF (aka PL-259/SO-239" connector, but that's really not what you should be worrying about. What you need on your coax is what you need to directly connect to on each end of the coax. Remember that it's perfectly fine to have different types on each end of your coax if that's what's required. The loss difference between "N" and "UHF" is only important if you can completely control what they connect to.

Most often a discone antenna will need a PL-259 on that end of the coax or you'll need an adapter to make it work. An adapter will have much more loss than any difference between a properly installed PL-259 and a properly installed N connector so you should go with a PL-259 on that end of the coax (if your antenna has a different connector requirement then by all means make the appropriate substitution).

Most often a scanner will have a BNC connector (they also often come with SMA so it pays to verify) so a BNC on the scanner end would provide the lowest loss. Note, if you have an SMA, a short jumper will probably be necessary since the SMA is such a small connector the LMR-400 will strain the connection if directly connected). If you use the jumper, it may be good to have that jumper premade with an appropriate SMA on one end and an "N" on the other end. Your coax should have the appropriate "N" on it so no adapters or barrel connectors are necessary (e.g. if the jumper has a male "N" have them put a female "N" on your coax).

As you can see from this, you will probably need different connectors on the ends of your coax. Your lightning arrestor should also be factored in and that may call for other type of connector as well, depending on what specific one you purchase (a good place for those low-loss "N" connectors if you haven't yet purchased it).

You want to avoid having to do what was needed in my situation going from a Mini-UHF male to a BNC male when my needs were immediate and supplier's selection was limited. I had to use a male-BNC to male-BNC barrel connector, a male-mini-UHF to female, and a female-mini-UHF to mini-female-UHF barrel connector. While it did the job at the time, it wasn't very efficient and made the connection an extra 3" long.
 

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ab3a

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I looked up the bend radius of LMR-400. It should be no tighter than a 1 foot radius, and I suggest using the repeating bend radius of 4 feet.

Look, this whole exercise is about loss. You want to keep that loss to a minimum. The less loss you have, the more you'll hear. At 80' with Type N connectors and fresh, genuine, properly installed LMR-400 cable you should expect a loss of about 4 dB from the antenna at UHF frequencies.

So if you're in the habit of listening to UHF traffic (800 MHz) then you really ought to consider quality coax and connectors.
 
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