Coax Comparison

[fourstringburn]

LMR 240 is RG8X size wise just as LMR 400 is RG8.

The LMR cable is really designed for losses that occurs in coax in the VHF range and above. HF frequencies are better off with solid or stranded RG8X type coax even though the spec's you read on losses and velocity factors can make you believe otherwise. If you look up spec's on Times Microwave LMR, you'll see the frequency losses aren't listed for HF frequencies below 30 MHz but they are spec'd for frequencies way up to the GHZ range at 100ft lengths.

Either coax works but for a truck install, RG8X will be just fine. Nothing much will be gained or loss with lengths well under 30ft on a mobile install. RG58 is fine unless high power is going to he used.

I use RG213 for my HF mobile rig because I need something stiff like a solid conductor in a stranded type coax. I have part of the coax exposed underneath the antenna and the bigger coax doesn't flop around in the wind like RG8X would eventually leading to a short at the coax connector.

 

[Redbeard U812]

After reading spec sheet find it has slightly higher velocity and attenuation. But not real impressed with the 4.5mm hybrid alum core, copper shield conductor compared to 9.5 AWG copper. Also, the Eco has 100% shielding factor for the copper foil and 72% with the copper braid, where Buryflex has 100% factor for alum. foil and 97% for tinned copper braid.

Though it's a trade off, I'm interested to find the cost comparison. I feel the Buryflex is built a little better, if significantly lower cost is factored, the Eco would be good for longer runs.

 

[338_MtRushmore]

The LMR cable is really designed for losses that occurs in coax in the VHF range and above. HF frequencies are better off with solid or stranded RG8X type coax even though the spec's you read on losses and velocity factors can make you believe otherwise. If you look up spec's on Times Microwave LMR, you'll see the frequency losses aren't listed for HF frequencies below 30 MHz but they are spec'd for frequencies way up to the GHZ range at 100ft lengths.

Are you saying RG8X is preferable for HF over LMR400? If so, I've missed the boat big-time, and need some more details please.

 

[Road Squawker]

Are you saying RG8X is preferable for HF over LMR400? If so, I've missed the boat big-time, and need some more details please.

100 watts,.. 100 feet of coax @27 MHz

RG8X 1.55 Db loss 69.9 watts at the antenna

LMR 400 .69 Db loss 86.4 watts at the antenna

 

[338_MtRushmore]

I'm familiar with the specs. Fourstring was saying that the specs were misleading, and RG8x was better than LMR at HF.

 

[Slowmover]

LMR 240 is RG8X size wise just as LMR 400 is RG8.

The LMR cable is really designed for losses that occurs in coax in the VHF range and above. HF frequencies are better off with solid or stranded RG8X type coax even though the spec's you read on losses and velocity factors can make you believe otherwise. If you look up spec's on Times Microwave LMR, you'll see the frequency losses aren't listed for HF frequencies below 30 MHz but they are spec'd for frequencies way up to the GHZ range at 100ft lengths.

Either coax works but for a truck install, RG8X will be just fine. Nothing much will be gained or loss with lengths well under 30ft on a mobile install. RG58 is fine unless high power is going to he used.

I use RG213 for my HF mobile rig because I need something stiff like a solid conductor in a stranded type coax. I have part of the coax exposed underneath the antenna and the bigger coax doesn't flop around in the wind like RG8X would eventually leading to a short at the coax connector.

Thanks.

 

[fogdog]

Bud or Bud Lite ?

 

[dave457]

100 watts,.. 100 feet of coax @27 MHz

RG8X 1.55 Db loss 69.9 watts at the antenna

LMR 400 .69 Db loss 86.4 watts at the antenna

I don't think those 16w will make a difference on the receiving end

 

[Redbeard U812]

Bud or Bud Lite ?

Shiner........

Now I am getting thirsty........

 

[Shockwave]

Sometimes the coax loss is not the most important thing to consider. The isolation the coax provides the signal inside, to the world outside can also be an important factor. Cheap cables often have less shielding. That can make a difference with interference on both TX and RX. Most only think about the signal leaking out of the cable and causing interference. The same thing can happen on receive. For example, if your coax passes by any equipment with a switching power supply you may get a constant noise level from outside interference leaking into your coax. All things to think about before the installation.

 

[w9cll]

Why would you run LMR-400 in a mobile install? You are running what 16' or so? It's not worth it, RG8x or even RG58 is now than adequate even running some power.

 

[Shockwave]

While I wouldn't pick LMR-400 for the mobile, RG58 might not be the first choice running any power either. Today's vehicles are very busy electronic environments and running low quality RG-58 at a couple hundred watts, parallel to any wiring harnesses or ECM could cause trouble. Increased opportunity for ignition noise to enter through poor shielding on coax too. There are good quality RG-58 cables available and even better alternatives still in that size cable.

If you have these problems in the mobile and coax leakage is not the problem, you may have a CMC issue on the coax. Guess what? Those RF ferrite beads that work on coax in the house, also stop CMC from coming back down the coax in the mobile. Everything from RF lip burns to mic feedback can go away placing one of them on the coax right at the antenna.

 

[Redbeard U812]

While I wouldn't pick LMR-400 for the mobile, RG58 might not be the first choice running any power either. Today's vehicles are very busy electronic environments and running low quality RG-58 at a couple hundred watts, parallel to any wiring harnesses or ECM could cause trouble. Increased opportunity for ignition noise to enter through poor shielding on coax too. There are good quality RG-58 cables available and even better alternatives still in that size cable.

If you have these problems in the mobile and coax leakage is not the problem, you may have a CMC issue on the coax. Guess what? Those RF ferrite beads that work on coax in the house, also stop CMC from coming back down the coax in the mobile. Everything from RF lip burns to mic feedback can go away placing one of them on the coax right at the antenna.

Changed the 58 in my truck to the Buryflex I had leftover from tower. Better shielding resulted in not having to use ferrite beads like you stated. Before placed one between radio and linear, and one right at antenna connection. Now none. Have also noticed ECM in truck not throwing codes. Have a programmer which I can view and erase codes, that had even been effected by RF feedback.

Good point there Shockwave

 

[Shockwave]

We also have to consider that cables with thinner conductors have more inductance too. That added inductance between the amplifier and exciter and the amplifier to antenna, can cause problems. That's one reason why some amplifiers without tuned input circuits often perform better when driven through the shortest cable possible. I know in the case of tube amps without an input circuit, the RF return path from the amplifiers input has to go all the way back to the exciters output stage. The other reason is the mismatch between the input and 50 ohm cable becomes worse as the cable is longer.

 

[fourstringburn]

Are you saying RG8X is preferable for HF over LMR400? If so, I've missed the boat big-time, and need some more details please.

Ok,

First off all I'm suggesting to this thread is that if the OP already have some good working condition RG8x installed on his mobile CB, nothing even slightly significant will be gained by replacing it with LMR240 just because the spec numbers look good. Once you compare the 2 types of coax on HF frequencies below 10 Mhz at 100 ft lengths, they are nearly identical.

The key here for comparisons is always at 100 ft lengths. Once you subdivide the lengths down to 20 ft or less for a mobile install or even 50ft or so for a base, the differences in losses seem trivial.


Other things to consider,

The skin effect depth at HF freqs is deep and you need a pure copper center conductor and copper shield like on RG type coax. Dielectric losses on HF are low so the center insulator can be a solid plastic type as used with RG213 or gas injected foam like RG8x.

At VHF & UHF the skin depth is shallow so the copper center conductor and copper clad aluminum used on LMR coax is OK but you need to have low loss center insulator like used on LMR cables because dielectric losses are high at VHF & UHF and beyond. This is exactly what LMR coax is designed for.

If you want the best, go with the large Heliax cables which is a hollow center conductor. That would be an extreme overkill for a mobile but if spec numbers really matter, go for it!

Remember, RF travels on the surfaces of a conductor not through the center of it. This is called the "Skin effect".



Here something to read...



LMR-400 for Ham Radio?


I see lots and lots of posts from people extolling the virtues of using LMR-400 coaxial cable in their ham radio setups. LMR (Land Mobile Radio) cable was developed by Times Microwave Systems as a high quality coaxial cable which can be used with excellent loss properties at frequencies greater than 1 GHz. If your ham radio interests lie in the 1.2 GHz band and above, I can see no reason why you shouldn’t use the LMR series of cables in your setups, since the more traditional RG series of cables often are out of specification above 1 GHz.

However, if you are running the usual 1.8 MHz to 54 MHz range of frequencies, I see no technical reason[*] why you should use the LMR series, especially LMR-400, based on the loss characteristic. Even at 144 MHz, there is not much difference between LMR-400 and good old RG-8 or RG-213. Sure, the double-shielded LMR series of cables has a better shielding characteristic, but you need to figure out whether this alone is worth paying the premium for.

Don’t get me wrong – I’m not saying that coaxial cable loss is trivial – the receive mode antenna system noise figure can be dominated by the feeder attenuation (loss), since for a passive device, the noise figure equals the insertion loss. However, I have noticed a lot of posts from people swearing by LMR-400 due to its low loss, even in the HF bands, and I somewhat disagree.

Here are some numbers via the Times Microwave Coaxial Cable Loss Calculator for 100 feet of cable:


Cable Loss (dB), 100 feet

To put this into perspective, if you’re running 100 feet of RG-8 or RG-213 and are thinking of upgrading to LMR-400 because of the loss you’re incurring, think again, especially if you mainly operate on the HF bands. Based on the above numbers, and a transmitter output power of 100W, the power arriving at the antenna using the same 100 foot length of the same types of cables would be:


Power at antenna, from 100W transmitter

So, if cable loss is your obsession, and that extra 4 watts is important to you on 40 meters, or if you think that extra 9 watts will make the difference to your QSO on 6m, then go ahead and use LMR-400. Remember, the numbers above are for 100 foot long lengths of cable, and it’s always good radio practice to reduce the length of your antenna feeder by as much as you can. When it comes to coaxial cable, less is more.

Also, remember that coaxial cables (even cable of the same type) are not constructed in the same way. Always examine a coaxial cable for shield coverage, and discard it if there is not complete coverage. Also, if you get the chance, heat up a piece of the shield braid and center conductor with a lighter flame and see how it is affected by the heat. Pure copper wire will glow while heated, but will hold its shape. Copper coated aluminum wire will glow, bend, and distort when heated.

Good luck!