RG-8X or RG-58 for mobile install??

Discussion in 'Mobile Radio Systems' started by W9DSD, Sep 13, 2011.

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  1. W9DSD

    W9DSD Ham Member QRZ Page

    I'm looking for cable recommendations for a mobile install. I'm mounting a 1/4 wave dual band antenna on the driver's side rear stake pocket of my truck. I'm going to route the cable along the frame where it exits the truck bed, and through the firewall into the cab, probably about a 15' run.

    Which type of cable will be the better one for this install, considering that it will be exposed to moisture under the truck? Thanks for your help.
     
  2. W1VT

    W1VT Ham Member QRZ Page

    I'd suggest a cable designed for direct burial, such as Times LMR-195-DB or LMR-240-DB.
     
  3. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    You really don't need any coax larger than RG8X. The lengths are short, so the difference in loss is just a few tenths of a dB. Any decent grade is just fine. The JWC RG8X sold by AES, and HRO, is just fine. And, there is another related issue, especially when operating HF.

    Almost without exception, most mobile installations end up with some common mode current. If you're careful, you can get 7 turns of RG8X through a 3/4 inch ID split bead. You end up with a CM choke of about 2kΩ at 10 MHz, and the impedance is mostly resistive, which is what you should strive for. If you were to duplicate the choke using RG8 sized coax, you'd need 49 ferrite cores. The cost differential is obvious.
     
  4. KF5FEI

    KF5FEI Ham Member QRZ Page

    If you are going to do 2m and up, go with LMR-240. 58 and 8X can be lossy at higher frequencies, even with short runs.
     
  5. W1GUH

    W1GUH Ham Member QRZ Page

    Practical suggestion -- get your coax jumpers from someone you know to make good ones or make them yourself. Me and a friend have wound up with jumpers that went bad (opened up somewhere) pretty often. And I gotta tell ya...a bad coax jumper can drive you up a tree -- can appear like something awful has happened to the antenna!

    Rule of thumb....

    If your antenna (fixed or mobile) seems to go bad "all of a sudden" check the coax connections FIRST!

    Have fun!
     
  6. N4EYZ

    N4EYZ Ham Member QRZ Page

    I ran 8x for hf and 2/440 to my 706 for over 10 yrs with never a problem. Ran under the truck too. Do it and don't worry about it.

    Wayne/n4eyz
     
  7. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    RG58 perhaps, but RG8X is better than most folks realize. If you just have to have lower loss UHF cable, then RG223 is the way to go. You'd best sit down for the price, however.
     
  8. WB0LSR

    WB0LSR Ham Member QRZ Page

    I'm with the LMR240 suggestion, although I'm not practicing that myself right now. My dual-band setup is running a short run of RG-58 presently, I've not had any real issues with losses, at least not according to what I measure at the antenna. LMR-240 has very low loss at higher frequencies, with better performance than 8X with the same diameter. It is a tad more expensive though.
     
  9. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    Frankly, in a mobile installation, and especially with FM, you will not be able to tell the difference between RG58/U, RG8/X, LMR-240, or even LMR-400 or LMR-600. You are going to lose more in the connectors than what you can lose in 10 to 15 feet of cable.

    Now if you are running mobile E.M.E. using CW or SSB, then you "might" see a difference and even then it is going to be so small that it won't make any difference unless you are operating in the SHF region!

    Glen, K9STH
     
  10. KC9SQR

    KC9SQR Ham Member QRZ Page

    If the antenna is being put on your truck for general local and repeater work, I'd just run the rg-58 and be done with it... That's what I've used for a while with results I can't complain about... As long as the coax run is short like 10-15 feet, I don't think you'll have any issues...

    Using my HT through about 12 feet of rg-58 I can get into the "255" from about 30-40 miles away :)
    I'd think that sticking a decent antenna with 3db or more of gain on the roof should offset any losses from the coax... But I'm only going by personal experience with my own setup...

    73
    Will
     
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