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've been giving my issue with SWR a lot of thought, and i think i'm gonna swap out the RG58 coax for LMR400 and see what happens. I have some extra laying around, and at this point i have nothing to lose. I think i may have gottten some crappy coax. It's the one thing i haven't tried yet. I'll use a short piece of something a little more flexible once i get into the cab and see if that improves the situation.


    K4LMP,

    What kind of power are you putting through your mobile??
     
  2. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    There is no reason to swap out the coax. The difference in power reaching the antenna won't increase more than about .25 dB. In fact, there is a reason not to. No matter the install, there is always some common mode current flow. Choking RG58, or RG 8X requires just one split bead with 7 turns. Equaling that with LM400 will take 49 split beads. As for power? Good quality RG8X will easily handle legal limit if the SWR is reasonable. With just 500 watts, RG8X will handle even 10:1, so the question remains; what perceived advantage do you think you'll have?
     
  3. K4LMP

    K4LMP Ham Member QRZ Page

    Dave, the power depends on where i'm at and what repeater i'm trying to get into. The radio is 50w on 2m and 35 on 440. I think in memory, I have most set at about 25 watts. I checked my swr with the analyzer, and all was well. I did check the reflected power on my meter, and it was minimal, not enough to worry about.

    Jeff
    K4LMP
     
  4. W9DSD

    W9DSD Ham Member QRZ Page

    You said it yourself in a previous post, where you stated that "bad coax just happens". I have nothing to lose by running the heavier cable. I have no clue as to the manufacturer of the current coax i'm using, other than the fact that it's an imported cable, and as a result, may very well be s@&!. It appears to be aluminum with a stranded center conductor.

    So, i am going to run the LMR400 just for giggles, grins, and the fact that i have nothing else to do tomorrow on my day off. I'll let you know how it turns out. I'm betting that the new cable will drastically improve my situation, and if not, at least i can say i tried.

    The antenna will primarily be used for 2M work, local repeaters as well as simplex. The 70cm end is primarily for use with the HT. Thanks for the advice.
     
  5. K7JEM

    K7JEM Ham Member QRZ Page

    The chances that it is the coax is very slim, especially since you already tried it with another piece. Your problem is most likely the antenna is too long, or the mount is giving issues. You never ran the simple SWR tests at various frequencies, so we really don't know. 20 minutes of troubleshooting and measuring trumps an hour of shotgunning.

    LMR400 is a poor choice to be using in a mobile setup, just makes no sense. But you will do what you want, makes me wonder why those of us that have tried to help even responded in the first place. There just isn't much to go wrong with a piece of coax. Check it for physical issues, check for shorts or opens, and it should be OK. Connectors are more often the culprit on coax cables, rather than the cable itself. We can only assume those were put on right.

    Joe
     
  6. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    I have had bad coax cable several times. That is why I won't purchase any more cable made by Coleman. What I use now came from AES (http://www.jscwire.com/jsc_ss.taf?p=3062) I've used about 200 feet of it off a 500 foot reel, and have had no problems. The best part is, it is made right here in the good old USA!
     
  7. KG6UTS

    KG6UTS Ham Member QRZ Page

    I used RG-141 on the Jeep mobile, short runs and same size as RG58 but better shield etc. It was purchased surplus.

    EdZ KG6UTS
     
  8. KB0MNM

    KB0MNM Ham Member QRZ Page

    Dave- See page 48 of the September 2010 QST magazine. W1ZR rates Belden 8259 (RG-58) for 2.2 dB per 16 ft. at 440 Mhz. Unless you want to waste a lot of money with hardline, this is the result that should be acceptable. I suspect that the 1/4 wave is not exactly correct- depending on which band. This post is devoted to my old associate Steve ( NAS )- who may not have been thinking about the reaction at higher frequencies. But then things do get warm in Arizona. 73-
     
  9. KB0MNM

    KB0MNM Ham Member QRZ Page

    Dave- You also mentioned moisture under the truck. This is something that you probably cannot escape. The real problem is all of the tiny little rocks that might hit the coax. Consider using a product like "convoluted loom tubing". This is something that can be purchased in many automotive stores ( at a rather large price per foot ), or through some trade suppliers. It is generally black and often called "Split loom". There is no problem with moisture nor even salinity from the roads if it cannot enter the cable shield. Use a good tape ( like 33+ ) if you want no repeats. 73 - Jon
     
  10. AD5MB

    AD5MB Ham Member QRZ Page

    W9DSD, have you read This web page about mobile radio installations?

    I am an electronic technician since JFK was in office and an electronics instructor since Richard Nixon lived in government housing and a tech writer, and I am awestruck by this web page

    forget split loom - use spiral wrap. much thicker, stands up beter to UV and ozone, you don't have to use tie wraps to keep things in.
     
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