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LMR240 versus LMR 400 - is it really that big a difference?

60K views 36 replies 11 participants last post by  redline 
#1 · (Edited by Moderator)
I need to run new VHF cable up the mast and have concluded from the research that either LMR240 or LMR400 would be the best choices for a 55' mast and probably another 15' of run to the nav station. Comparably, LMR240 is half the size and twice the attenuation loss as LMR400, but this still doesn't seem huge and either one seems to be the highest quality and lowest loss option for marine coax. There is also the DB (waterproof) version.

I am leaning toward the LMR240 because of its smaller diameter and would run the cable up with a messenger line. I am also scheduled to do the haulout toward the end of March so could drop the mast, if pulling the cable up doesn't work. Just want to do a sanity check with those who have more knowledge of these things. The old coax is 28 years old and probably all the cables/wiring are going to get replaced. I have a new mast headlight and NMEA 2000 anemometer that need to go up, too.
 
#2 · (Edited by Moderator)
I need to run new VHF cable up the mast and have concluded from the research that either LMR240 or LMR400 would be best choices for a 55' mast and probably another 15' of run to the nav station. Comparably, LMR240 is half the size and twice the attenuation loss as LMR400, but this still doesn't seem huge and either one seems to be the highest quality and lowest loss option for marine coax. There is also the DB (waterproof) version.

I am leaning toward the LMR240 because of its smaller diameter and would run the cable up with a messenger line. I am also scheduled to do the haulout toward the end of March so could drop the mast, if pulling the cable up doesn't work. Just want to do a sanity check with those who have more knowledge of these things. The old coax is 28 years old and probably all the cables/wiring are going to get replaced. I have a new mast head light and NMEA 2000 anemometer that need to go up, too.
Whichever one you get, choose the "UF" suffix, e.g., LMR-400UF. These are "ultra flexible" and will be easier to deal with.

I'd choose LMR-400UF over 240 for run like yours, but I might go for RG-213 or, better, RG-214 for several reasons, including terminations. Be sure yours are professionally done, if possible.

A good source for cable, connectors, etc. is: RF Connection Coaxial Cable

Bill
WA6CCA
 
#4 ·
I believe the LMR cables have foam dielectric and the RG-213 and 214 are solid. The foam dielectric will have lower loss, but is more fragile especially around tight radii. Also more challenging to solder the connectors to without damage to the foam.

Losses are pretty high at VHF. Even with a well-matched antenna, difference in loss between the 240 and 400 is probably 2 or 3 dB for your 65 or 70 feet of cable. Any of them will work fine for short-range signals. Not sure what the cost difference is, but I'd probably splurge on this assuming I can fit it in the space available.
 
#7 ·
Thanks, MaineSail. Love all the info on your website. I had seen a YouTube video for making the VHF connections. It said to peel back the shield, which someone criticized in the comment section, but didn't say what to do instead. You flared it. That's helpful to know. The video also showed them soldering the pin to the conductor, but you did not do this. I understand that it could be easy to damage the dielectric, but on another site, they placed a metal shield in front of the dielectric. Would the soldering better ensure a good connection?

It's also interesting that the Times Microwave site says that LMR 400 UF has a life expectancy "in excess of 10 years" while LMR 400 is in excess of 20 years. Is this because the UF cable material is less robust to UV or other damage? Anyone know?
 
#8 ·
I need to run new VHF cable up the mast and have concluded from the research that either LMR240 or LMR400 would be best choices for a 55' mast and probably another 15' of run to the nav station.
I usually run coax down the mast (*grin*) since more often than not I run new coax with the mast up. Make your masthead connection on the ground and take the whole bit up the mast.

I am in accord with Bill (btrayfors) and RC (Maine Sail). LMR400-UF, RG-213, or RG-214 are the best choices. Do not abandon wires in place in the mast. Pull out anything you aren't using.

Bill (I think) and I both prefer solder-solder silver teflon connectors. RC has a particular brand of solder-crimp connectors he has had good experience with but I have not tried them yet.

I would not use LMR240 or RG-8X if I could avoid it. I use RG-213 or RG-214 at HF so I will certainly use it at VHF.
 
#9 ·
Thank you, Auspicious. That answered some questions. I had actually been thinking of running the wire *up* the mast because it seemed that hauling 55' of cable would be hell, but how I'd crimp and solder while dangling up there is probably completely unrealistic.

Maybe I should have entitled this: what's the difference between RG-213 or RG-214 and LMR 400? It looks like RG cable is much more expensive than LMR, but in my reading, it seemed that LMR had less loss than RG. I can't seem to find much that compares the merits of RG versus LMR.
 
#16 ·
Maybe I should have entitled this: what's the difference between RG-213 or RG-214 and LMR 400?
One thing to look at beyond the size of the cable, is how much loss there is. You transmit 100 watts of power from the radio, not all the power is coming out at the other end. The higher the loss, the worse the cable is. Something might work well for HF, but when you get into the higher VHF/UHF frequencies, it might be pretty bad and you could end up losing half your power in the cable before it gets to the antenna.

Since you're looking at using the cable for VHF use, this is what I found for the cables you are considering at www.universal-radio.com

The higher numbers are the worst ones.

RG213
Attenuation (dB per 100ft)
100Mhz 2.1
200Mhz 3.0

RG214
Attenuation (dB per 100ft)
100Mhz 1.9
150Mhz 2.8

LMR-240UF
Attenuation (dB per 100ft)
146Mhz 3.0
150Mhz 3.0

RG-8X
Attenuation (dB per 100ft)
100Mhz 3.0
146Mhz 4.5
150Mhz 4.7

LMR-400UF
Attenuation (dB per 100ft)
146Mhz 1.5
150Mhz 1.5

So you can see why people are recommending LMR-400UF over the other types. It has a lot lower loss so more of the power you are transmitting will actually get to the other end. Ideally, you want the lowest loss cable you can get for the frequency it'll be used on.

Hope this helps.
 
#10 ·
The LMR uses a closed cell foam dielectric where the RG-213 and 214 uses a solid plastic. The LMR will be much lighter and have lower losses. The only real minuses would be less physical toughness and somewhat more difficult to solder on the connectors - due to the foam. Since most of it will be in the mast, I'd probably go with LMR400 UF if it were me. You could transition to something else once it exits the mast. For shorter jumpers, I'd use LMR 240. You just have to avoid crushing the LMR. RG-214 is probably overkill. LMR is widely used in commercial applications and is electrically superior, really.

For making up solder joints at the top of roofs, masts and towers, there is this butane-powered soldering iron:

Robot Check

Learning to solder coax connectors takes a bit of practice. Plenty of guidelines available on-line. Just buy top drawer connectors. You need a high output soldering iron to quickly heat the large connector body without melting the coax dielectric. Having some pre-made with connectors is a nice option.

For coax and connectors, a good resource is the Wireman: https://thewireman.com/products.html At least I've had good luck with them in the past. You could give them a call with whatever questions you have.
 
#18 ·
The only real minuses would be less physical toughness and somewhat more difficult to solder on the connectors - due to the foam.
Agreed. The foam melts faster than the plastic. Equipment and skill make more of a difference.

You could transition to something else once it exits the mast.
Not if you can avoid it. Almost every transition means two connectors and an adapter. If you shop around you can get inline SO239 connectors and avoid the adapter. Good luck attaching that by the way.

The best approach is a long pigtail that is the end of the cable down the mast and routing that through the boat to the VHF. Yes you have to pull it back when you lift the mast. Yes you have to route it again when you step the mast. It is a huge improvement over a connector at the base of the mast.

For making up solder joints at the top of roofs, masts and towers, there is this butane-powered soldering iron
Sure. At the top of the mast with a moving target and the wind blowing. I have one. If I have to do work at the masthead I use a higher output propane plumbing torch. More heat, more focus, more control, less dwell time, fewer errors. Best is to do your soldering on the ground.

You need a high output soldering iron to quickly heat the large connector body without melting the coax dielectric.
For torches counting as irons then absolutely correct. You want lots of heat (high thermal inertia if you use an electric iron) for the least possible amount of time.

I'd just emphasize that having a BIG soldering iron is key. You want to be able to heat the connector as fast as possible so the solder will melt on the connector before the dielectric melts.
You said it twice so I will also. It is important. It is key.

So is practice.
 
#11 ·
Awesome, K7EL. Thanks for repeating your comments on the differences and the additional info. I appreciate everyone who answered my many questions! I'll practice soldering those connectors first and test them. I'm cognizant of the problems if I do this wrong, but it seems very doable. We'll see :)
 
#12 ·
Gamayun,

It is quite do able, just requires patients and preparation, 95% to 99% of my time soldering components and connectors is in the preparation for soldering. It also takes practice, so practice practice practice.
 
#15 ·
I've used LMR-400 before on an 80' ham radio tower and that is some stiff stuff. So agree with using the UF type for better bending. I'm planing to use the LMR-400UF myself for a new radio setup between the radio and the mast step, replacing the 35yr old cable on the boat now.

Hope it works out for you.
 
#20 ·
A pigtail is a length of cable coming out of the mast that's long enough to reach the VHF head unit wherever it's mounted in the cabin. In other words, use a cable that's long enough to travel from the masthead, out the bottom of the mast, and then to the radio. There'll be just two connectors, one at the masthead and one at the VHF.
 
#21 ·
Ah yes, now I understand. I was planning on making a jump at the mast base to make it easier to separate when pulling the mast. Perhaps SV Auspicious is saying that a pigtail is huge improvement over a crimp connector at the point? And then make just one connection at the masthead. I'm thinking that the decrease in lifespan of the 400 LMR UF has to do more with its flexibility than with UV damage. I'm hoping that's the case. Maybe an extra long piece of heat shrink around any exposed cable would help....
 
#22 ·
The manufacturer specifically rates it for 10 years of UV exposure. Without UV exposure (or with a secondary UV shield on the short exposed bit at the top of the mast) and with good soldered connections, it should last multiple decades.Yes, SVA is saying that the fewer connectors, the better. Unless you pull your mast every year, there should be no need to put a connector at the base of the mast if it's not a huge PITA to get the cable end to the VHF head. Since you're in San Francisco, I assume you don't pull your mast for the winter so I agree with his advice even if it's a bit of a run from the Freedom's mast base to the typical VHF location on that model.
 
#23 ·
Hmm, it is a bit of a run with multiple turns and that would be a PITA (to me). The mast is far forward than a typical boat and the nav station near the companionway. I'll have to think on that. I have never pulled the mast, but have only had the boat for 3 years. I am considering it during the haulout in March, especially if I run into trouble with the wiring.
 
#24 ·
gamayun,

While a PITA with one long run, it will in most cases save you from being a PITA when you need it most in foul weather and you need to make a call, each connection you make, e.g. each extra cable adds loss due to mismatch of impedance of the transmission line, the coaxial cable, this reduces your transmitted power available at the antenna. Each additional connection is also a potential point of failure, keep your loses due to mismatch low and the potential for failure also low by minimizing the number of connections you use. How much loss, depends on several factors and are beyond the scope I am willing to go into for this post, but realize any added connection will add loss to your transmitted power and it could be substantial, a 3 dB loss while it seems insignificant is actually a loss of half your power, e.g. radio transmits 100 watts, antenna only transmits 50 watts, you have lost 50 watts to impedance mismatch and heating of the coax lines.

In short, if you can keep the connections to one cable, two connections; one at the radio and one at the antenna you will be better served.

I will now step down of the lectern,

Thomas
BSEE/BSCPE
KK4UHH
 
#25 ·
Regarding connectors and losses - too much is being made of this. Assuming a well-made connection, losses will be immeasurable. There is a professional who has posted actual experimental measurements on other forums. He connected a ridiculous number of various types of connectors - even including BNC and other non-vhf connectors and saw 0.1db loss at VHF frequency through the entire mess.

I wouldn't hesitate in the least to add a connector if it meant avoiding a difficult snake through the boat. Particularly if one needs to pull the mast regularly, especially if using a larger, stiffer cable like lmr400.

Mark
 
#26 ·
I agree with Mark: the losses due to additional connections have been proven to be minimal, at least at the HF and VHF frequencies we're talking about.

However, Thomas KK4UVH is correct about the potential losses from additional connections. This may be due to poorly-installed connectors, additional surface corrosion potential, moisture ingress for badly sealed connections, poor choice of connectors, etc., etc.

Bottom line: use the minimum number of connectors feasible for your installation, but don't be paranoid about an additional connection if this is really necessary in your situation. But, if it is, then be 100% sure that it's done correctly with the best quality components and practice.

Bill
WA6CCA
 
#27 ·
I agree with the points made and can see both sides. One fun thing I've learned in sailing is that there is never just one way of doing anything, but I completely understand how a proper connection can mean the difference between having reception for many miles to not being heard across the marina. I do want to get this right (the first time) and the input here has been very educational for me. I'll let you know how it goes. Thanks all!!

Oh, I used to be KG4CJT till I let my license lapse. The Ham community is very much like the Sailing community. Always super helpful :)
 
#29 ·
A bit of a derail here, my mast has a small, plastic track to encase the wires and protect them from the halyards, I assume. Right now the old cable runs up the tube along with the nav light wires. How would one fasten the LMR400 (it won't fit down the tube)or do you let it float in the mast?
Thanks
Brad
On the hard next to Lake Huron, still no ice!
 
#30 ·
Dave, I'm sure you have seen John on Laurie Ann's experiment with connectors. He did not see even a 0.2db (your low end for a single connector) loss through a large number of connectors - several of them BNC and SMR types.

For fun, I just stuck 6 various connectors, pigtails and barrels into our VHF. VSWR before: 1.1:1, VSWR after: 1.1:1. The two barrel connectors were cheap 99 cent ones, and a 3' pigtail was rg58.

I don't have a db meter, but according to your post, I should expect 1-3db loss. I doubt I'm seeing that- I doubt there is any practicle loss at all.

Mark
 
#31 · (Edited)
Unfortunately you cannot make the assumption that just because you have a low VSWR means you have low loses, it simply means that your transmitter, transmission line and antenna are properly match or TOTALLY mismatched, read on. One could have High loses and a low VSWR simple stating I have a VSWR of 1.1:1 does not mean you have low loses.

How you say: here is how

VSWR = (1+the square root of (Power reverse/Power Forward))/(1-the square root of (Power reverse/Power Foward))

where power reverse is the power measured reflected back by the antenna and power forward is the power sent from the transmitter.

so imagine this scenario 3 dB total loses and a reflected power of say 0.1 watts when transmitting 25 watts at the transmitter.

your VSWR at the Transmitter is 1.14:1 not bad VSWR but your transmitted power is only 12.5 watts, or 50% of your transmitted power at the antenna, if your loses where 6 dB you would be transmitting 6.25 watts, yet your VSWR can stay the same.

How can this be, the very nature of VSWR, is that the power is reflected back down the transmission line toward the transmitter, or point of measurement, it does not take into account loses along the line which manifest themselves in the form of heat. It is possible in fact to have a VSWR of 1:1 and not transmit anything, as all the power is adsorbed in losses and no power is reflected back down the line.

So please do not assume just because you have low VSWR you have low losses. You can have low VSWR and high loses as VSWR is just a ratio of Forward and Reflected power it is not a representation of loses. One can have a low VSWR and have high loses.
 
#35 · (Edited)
colemj,

My apologies, misread your post, lumped the last two statements together. Having 30 years around RF equipment, as a technician first and now as an engineer, I have had to many discussion on the differences between VSWR and losses. Many seem to lump the two together and have difficulty separating the two concepts. As VSWR can be corrected for and is with an antenna tuner or and impedance matching device, but losses are just that losses they are gone.

Bottom line when dealing with any RF transmission system keep the connection to a minimum, avoid tight radius bends that could damage the coax, keep the connections clean and free of corrosion, keep the connections tight and properly mated but do not over tighten. I have found by adhering to these principles that any problems I have are usually in the equipment not the transmission lines and antenna, and when I have not verified these often times I find the problem there.
 
#36 ·
Came across this article in the New York Times today about the discovery of gravitational waves. Many of the researchers who were instrumental in the work have now retired, one has dementia. One of them is still a tinkerer in the lab. The NYT reports that "[o]nly three days before the black hole chirp came in, Dr. Weiss was at the Livingston site...and was horrified to find that the antenna readings were plagued by radio interference. That needs to be fixed, he told his colleagues, imploring them to delay the engineering run. But they demurred, saying that everything was ready, that it was too late to stop the program. Lucky for them. "We would have missed that big event," Dr. Weiss said."
 
#37 ·
I too have one of those long somewhat twisty runs from mast base to nav station, so a connector at the mast/deck is not optional. What I can recommend heartily is the CableClam or similar fitting which goes over the cable and let's you put the connector inside the boat where it stays nice and dry.
There's nothing I hate to see more than a pair of PL259 plugs back to back with a bit of tape over them at the bottom of the mast. Usually in the way, easily stepped on, and ideally placed for water to run down the cable into the joint.
The larger CableClams can accept more than one cable, and the base opening is large enough to accept a coax plug or radar connector.

(Redline has 9 cables coming out of the mast, so those connectors *have* to be kept inside out of sight!



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