Antenna/Feedline selection for Mobile Install

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KN4SLJ, Jun 7, 2019.

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  1. KN4SLJ

    KN4SLJ Ham Member QRZ Page

    Hey guys. I'm fairly new to the hobby and am planning on relocating my iCom ID-4100 to my truck alongside or in place of my CB. I have a run of Belden RG-8x already running to the front driver side stake hole mount for my 5ft Firestik CB antenna, and enough coax for a separate run to the opposite stake hole if necessary. I know that RG-8x is less than ideal for uhf/vhf use, but in real world use does it make a big enough difference in a 20ft run to matter or is there some other kind of flexible feedline that I should invest in? I also have some LMR-400 but it may be...difficult to do a mobile run with that. If I don't replace the CB, I'd like to mount the dual band antenna on/in the passenger side front stake hole, opposite the Firestik. I would prefer that it be fairly large to get some altitude over the cab of the truck. It's one of the aluminum body F-150s. I read that the aluminum would be a poor groundplane but on 11Meter my SWR is 1.1:1 so I dunno. Maybe it would be more pronounced with UHF/VHF. I was looking at the ~5ft Comet CSB-790A antenna but haven't found any reviews on it and some others don't have kind things to say about the Comet brand in general. I have no experience one way or the other and I was hoping somebody could make a recommendation. I wouldn't mind spending more for higher quality but I don't even know what to look for. I currently have the radio in use as a base station on a Tram 1480 to good effect, but I think I'll just get more use out of it if it's mobile. Now that I've learned about HAM, the shenanigans on 11 Meter makes my skin crawl. One dude was whistling and splattering over 15 channels the other day. I kid you not... Anyway, any thoughts or suggestions on how I should proceed?
    Last edited: Jun 7, 2019
  2. NH7RO

    NH7RO Ham Member QRZ Page

    The RG8X will be OK for a short run, at least for starting out on 2m. Comet and Diamond are also fine; I've been using a Comet dual band for years in my mobile w/o any issues. A Larsen NMO mount centered in your roof is probably about the best way to go if you want the best and a simple 1/4 wave (19") is all anyone needs for 2m/70cm in general. The 70cm band is the third harmonic of 2m so one antenna will perform fine for both bands.

    By the way, "ham" is not an acronym---no need to capitalize it as such---ever!

    Ham radio is a great hobby and I'm sure you will enjoy it having been through the CB scenario already; a lot of us also got our start the same way.


    K0UO, W6KCS, KC8VWM and 1 other person like this.
  3. KN4SLJ

    KN4SLJ Ham Member QRZ Page

    My apologies on the ham thing. I feel like if I don't capitalize it then I'm taking about a delicious meal instead of a cool radio hobby.

    What type of feedline is preferred for a mobile 2m/70cm run? I don't need a lot of it so a purchase is not out of the question. I wish I could put it on the roof, but the body being aluminum precludes the use of a magnet mount and there isn't enough alcohol in the world to make me want to drill a hole in the roof of my new truck lol. With 11 meter they said to get the antenna loading above the roof line if at all possible. That's why I got a tall top loaded antenna. I could always get a shorter vhf/uhf antenna, but with it mounted on the bed wall/stake hole it will only barely peek over the roof. Would that be a deal killer or would it be okay?

    Sorry to keep on. I'm not ashamed to ask a question or two.
    NH7RO likes this.
  4. WZ7U

    WZ7U Ham Member QRZ Page

    Stake pocket is a poor choice for locating the antenna but I suspect you already get that. As a compromise solution, it will work, just not as good as it could in a better spot like on top of the cab. RG8X works for short runs, the loss in that case isn't large enough to get your panties in a wad. LMR400 works great but is kinda stiff for that application. One choice nobody considers much is quad shield RG6. It can be made to work with a little ingenuity. Cheap and handles a bit of power too. JMO. See here -

    In case you aren't aware of this site, check it out. Carve out some time as it is quite extensive.
    NH7RO likes this.
  5. KN4SLJ

    KN4SLJ Ham Member QRZ Page

    Excellent site. There's a wealth of info there and I am going to be reading it. Thank you. The stake hole is definitely a compromise. That's the main reason I'm concerned over antenna and feedline choice. Both of those options are under my control...within reason anyway. Performance as a base station has been outstanding and I just want to lose as little of that as possible. Thanks again.

    NH7RO likes this.
  6. W5LZ

    W5LZ Ham Member QRZ Page

    The key word in this so far has been a "short" run of feed line. In almost any vehicular installation you are talking about a short run. Not all installations, but how many people have that long of a car/truck? As also said, almost any coax will work on VHF/UHF if it's a short run. You honestly won't gain anything by using 'whatever' bigger/larger/better than RG-58, or RG-8X. That's true about getting a signal from the radio to antenna and the other way around. When you start talking about how much transmitted power you run, then things change a bit. For the average VHF/UHF radio you aren't talking about a lot of power in a mobile.
    There's nothing in this post that hasn't been said a million times, so no super great revelations...
    K7MH and NH7RO like this.
  7. NH7RO

    NH7RO Ham Member QRZ Page

    This may shock you a bit---but if I had a brand new truck I'd be absolutely itchin' to punch some holes in the roof! So many bands, so little time---and the center of the roof has been proven to be the absolute best spot for mobile antennas. Sorry I forgot to direct you to Alan's fine site (K0BG) but WZ7U did so already. Have fun and feel free to keep asking questions; that's what we're here for anyway.


    K0UO and K7MH like this.
  8. K7MH

    K7MH Ham Member QRZ Page

    Absolutely fearless! I like it!:)

    In as much as Larsen antennas are heralded as the greatest thing since peanut butter by the ham community, their antenna mounts and such I suspect are held in high esteem as well generally speaking.
    They don't use any cable that is particularly super duper when you buy one of their mounts that include cable. They know short runs like that in mobiles do not share the same concerns that a long run at home might have.
    They don't dwell on it so neither do I. I used to have some RG58 Superflex that I really liked. It was just easier to work with. I usually use NMO mounts that come with the cable already attached and just use that.
    If you will just be on FM and using a lot of repeaters you are not exactly doing weak signal work where you need every bit of signal you can get.
    Last edited: Jun 8, 2019
    NH7RO likes this.
  9. W6KCS

    W6KCS Ham Member QRZ Page

    RG-58 is fine for VHF/UHF. I use the double-shielded fancy version which is RG-223, but they are both low loss, the stuff I've tested is around a dB for six feet at 1 GHz, so low you wouldn't notice in a typical mobile installation.
  10. KN4SLJ

    KN4SLJ Ham Member QRZ Page

    Thanks for all the help, guys. Looks like I'll be going with a Diamond sg7500nmo 41" and the leftover Belden rg8x from my CB install. I also checked out some attenuation charts and they echoed what you have told me. I figured I'd also mount a nmo L bracket just beside the stake hole inside the bed instead of actually IN the stake hole. Drilling holes in the bed wall isn't too bad. The roof though... Phew. Makes me sweat just thinking about it. I'd like to rig up some kind of mast at the front of the bed by the back window to get the antenna base above the roof line but I don't know how I'd go about it. I don't have a welder so fabricating something would be problematic.

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