LMR-400 on a repeater

[kmcdonaugh]

So I have had some people swear up and down that LMR-400 should not be used on a repeater. That after some time the sensitivity will degrade and it "will cause noise". Now for what I use mine for, it is probably good enough. But I have researched a little bit, and found that yes, for repeaters that experience heavy use this could eventually become an issue. However, it seems that is the case for regular LMR-400. I have found that this noise is actually from wire braid coax, and that you can actually buy LMR-400 that isolates the the two shields so the wire braid is not touching the foil, and does not cause the noise. My question is, is this a serious enough problem for the average repeater owner to even care? My opinion is no.

[SteveShannon]

11 minutes ago, kmcdonaugh said:

So I have had some people swear up and down that LMR-400 should not be used on a repeater. That after some time the sensitivity will degrade and it "will cause noise". Now for what I use mine for, it is probably good enough. But I have researched a little bit, and found that yes, for repeaters that experience heavy use this could eventually become an issue. However, it seems that is the case for regular LMR-400. I have found that this noise is actually from wire braid coax, and that you can actually buy LMR-400 that isolates the the two shields so the wire braid is not touching the foil, and does not cause the noise. My question is, is this a serious enough problem for the average repeater owner to even care? My opinion is no.

My third party observation of other people’s reports of LMR 400 losing sensitivity is that it’s caused by moisture entering the cable at the connectors.  With proper waterproofing, ideally N connectors rather than UHF connectors, and higher quality coax in the first place (I have M&P that I’m pleased with) I wouldn’t expect degradation.

Now with that said, if your run to the repeater is very long at all you’ll want to use something intended for low loss at UHF frequencies such as hardline. At GMRS frequencies you lose half your power every 100 feet for LMR400.

[Lscott]

2 hours ago, kmcdonaugh said:

So I have had some people swear up and down that LMR-400 should not be used on a repeater. That after some time the sensitivity will degrade and it "will cause noise". Now for what I use mine for, it is probably good enough. But I have researched a little bit, and found that yes, for repeaters that experience heavy use this could eventually become an issue. However, it seems that is the case for regular LMR-400. I have found that this noise is actually from wire braid coax, and that you can actually buy LMR-400 that isolates the the two shields so the wire braid is not touching the foil, and does not cause the noise. My question is, is this a serious enough problem for the average repeater owner to even care? My opinion is no.

The link below goes into a bit more detail on the subject.

https://www.repeater-builder.com/antenna/double-shielded-coax.html

[SteveShannon]

15 minutes ago, Lscott said:

The link below goes into a bit more detail on the subject.

https://www.repeater-builder.com/antenna/double-shielded-coax.html

That’s a good point.  Out of laziness or bad habits, I tend to equate the various coax cables that are similar to LMR400.  LMR400 is the cable made and sold by Times Microwave which does have an aluminum foil shield and a copper braid with a solid copper inner core.  

The actual cable I use is a Messi and Paolini product.  Their Ultraflex 10.3 mm cable has copper foil and copper braid shields and a stranded copper core..

[Radioguy7268]

Count me as one of the guys who uses LMR-400 (the actual Times Microwave stuff) on a regular basis. I'll use it all day long for rooftop sites with a coax cable run under 50 ft. I'll use it for both UHF and VHF. I won't even blink at using it when price (bidding) is a consideration. If money doesn't matter, and the folks are willing to pay for Heliax (CommScope LDF-x50A) then buckle up & let's build something that's going to last 40 years.  Otherwise, I'm going with a likely 10-15 year job and paying attention to waterproofing the connections. If you're running 100 foot of cable, or going up on an actual Tower site, then the math starts to work in favor of springing for the good stuff.

Oh, and for all the hammy's out there that scream about using LMR-400 - it's probably those UHF PL-259 connectors that you keep soldering on that ruins the job, not the cable. 

I can easily count the number of jobs I've ever had to go back to due to a high noise floor from failed LMR-400. The answer is Zero. I've been doing this for close to 30 years now. People let theories of perfection get in the way too often.  Crap like tin plated connectors and poor workmanship are more likely the cause of cable problems. You can look for value - just quit buying junk connectors that are 25 cents less than the next lowest price you can find online.

[JohnE]

From personal experience wish I still had the pics

LMR 600 long story short the outer casing on the cable becomes porous and water migrates into it. at best in the NE 5-7 yrs and it needs to be changed. 

As a sub for 400 I sometimes use FSJ 2. Similar size and loss