LMR400 or RG8 or ???

Discussion in 'General Technical Questions and Answers' started by KC2UYZ, Apr 4, 2009.

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  1. KM3F

    KM3F Ham Member QRZ Page

    If you intend to get into serious weak signal work on SSB and EME at 6m and above, get the best you can afford for loss per 100 feet....and...... the connectors can be an issue depending on how serious you become.
    My experience is that PL259 UHF hardware is not the best to use above 6m.
    The next level is type N connectors for any coax, semi hard and hard line.
    This hardware is much more expensive than the UHF types, so do yourself a favor and get the best installation the first time so you don't have to redue it it later.
    UHF hardware does not keep the impedence match at each connection point such that when you look as VSWR you are looking at a large sum of all the disruptions in the transmission line besides the line loss.
    Switching antennas at the far end of a single transmission line also demands the best antenna relays you can get hold of.
    I have been experimenting with all this on temp antenna installations and see all the issues that contribute to a good system and what it cost to install tbe best system to meet my needs.
    I have been advised by many people that LMR 400 would be good enough but that is their position not mine. I will be going with LMR 600 or more likely larger Heliax line very shortly for up to 70 cm permant installation.
    Remember that 3db loss per 100' at 400 mhz is half your transmit power waisted as well as recieve sensitivity.
    Last edited: Apr 5, 2009
  2. K9KJM

    K9KJM Ham Member QRZ Page

    As already pointed out, Choice of coax depends on a number of factors.

    For HF, Most any coax will do. RG 213 is generally considered the "Cadillac" of coax for HF, Something like Belden RG 8X works just fine on HF for a 100 foot run. (RG 213 type is LOTS "tougher" than foam filled LMR 400. You could run RG 213 over with a truck and not have a problem!)

    There are several types of Times LMR 400, Solid center conductor (.79 cents a foot in short lengths) And "Ultraflex" for going around rotors, etc.

    While some "Clone" types might be OK, I dont see much of a reason to take the chance. If you buy the real thing, TIMES LMR 400 in a bulk spool of 500 feet from one of the distributors, You can get it for as low as in the .50 cents per foot range............

    LMR 600 IS good coax, BUT the price of the connectors is high. A person is really MUCH further off just getting the REAL thing, Something like a roll of good used Andrew LDF5-50A 7/8" Heliax (Or similar) good used at a swapfest for LESS money than new LMR 600 would cost! IF you need to run longer than the 70 or so feet that LMR 400 is good for at UHF..........
  3. K3DAV

    K3DAV Ham Member QRZ Page

    Only one slight difference.

    I have 3 antennas. 2 of them are fed with Times Microwave LMR-400. The 3rd is fed with the generic that I got from a friend.

    The only difference I could see between them is, the foil wrap around the foam on the Times Microwave was molded directly to the foam insulation. You would have to slice it with a knife and shave it off to remove it. However, with the generic 400, the foil was just wrapped onto the foam and could easily be unwrapped and removed. Other than that, they were identical.

    As the rest of these guys have said, on HF it will work with any fair to good coax. But for 2 meters and up, the Times Microwave LMR-400 is the next best thing to hard-line. The solid copper center conductor, and the foil molded to the foam assures a "close enough" to 100% shielding. The loose wrapped foil on the generic 400 may or may not have a small effect on the amount of shielding. But the difference will be barely noticable at best.

    The only thing to be careful about with LMR-400 is not bending it too tightly. It will make a kink you can't remove. For myself, I would rather spend the few extra pennies for the Times Microwave LMR-400. But to each his own.

    Good luck.
  4. KC2UYZ

    KC2UYZ Ham Member QRZ Page

    Hey thanks....but someone here said LMR400 has a solid aluminum core flashed with copper. Which is correct?
  5. KC8VWM

    KC8VWM Ham Member QRZ Page

    Don't need to focus on whether the "core" is solid copper or not because it is the "skin effect" of such a conductor that really matters. The bulk of the conductor merely relates to the conductors power handling capabilities.

    In addition there are better transmission lines than LMR 400 that are "closer" to hardline in terms of reduced line loss specifications. For example LMR 600 etc..

    My Best, Charles - KC8VWM
    Last edited: Apr 6, 2009
  6. K7JEM

    K7JEM Ham Member QRZ Page

    It is AL with a copper coating. It makes it much lighter than a solid copper center, with similar attenuation, due to skin effect (as noted).

  7. KC2UYZ

    KC2UYZ Ham Member QRZ Page

    Thanks Joe and Charles. Much appreciated.
  8. K3DAV

    K3DAV Ham Member QRZ Page


    Sorry ZIFF, my bad. It is aluminum with copper flashing. It's still the best bang for the bucks. Thanks for the correction guys.
  9. K9KJM

    K9KJM Ham Member QRZ Page

    TIMES LMR 400 is made in several different versions. The plain (cheapest) version has a solid aluminum center conductor that is copper clad. Works great for all but an installation that needs constant flexing. (Like around a rotor) TIMES LMR 400 "Ultra Flex" has a stranded copper center conductor, (And costs more)
  10. N1JBS

    N1JBS Ham Member QRZ Page

    Putting connectors on Lmr-400 is no harder than regular Rg8/u if you have a Sharp Knife.
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