Best Coax for Long run HF?

Discussion in 'On-Air Operations - Q&A' started by KM6KRE, Feb 28, 2018.

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  1. KM6KRE

    KM6KRE Ham Member QRZ Page

    Good morning,

    I'm sure this is a repeat question but I've been digging around for several hours and can't seem to find a solid answer. I'm in an HOA, luckily I'm next to the easement, and would like your opinion as to the best coax for my set up.

    I plan in running legal limit at 250-300 feet. I think I'll need a "hard line" in between my end feed EFHW-80-10-HP antenna and my entry panel into my shack. The loss calculator I've used for that length of LMR 400 is almost 50% in 10 and 20 meter bands. LMR 600 is ridiculously expensive for length of a run but the losses are less.

    Looking for recommendations/suggestions.

    Thank you,

    Wade
    KM6KRE - no longer in CA, just moved to VA. FCC is up to date, just waiting on QRZ to run another database sweep.
     
  2. KD0CAC

    KD0CAC Ham Member QRZ Page

    Seems as though you have several wrong details ,
    LMR 400 is not hard line .
    And 50% loss at 10m is off by close to double .
    http://www.timesmicrowave.com/calcu...ency=10+MHz&runLength=300&mode=calculate#form
    One of the thing to lookout for , is some of the labels for coax are generic - so multiple manufactures , so the spec.c vary .
    I try to avoid the word best , and even worse additives , super etc.
    As an example best could go in 2 different directions , 6' coper pipe [ have not worked with commercial hard-line like this , but have been around it ] or a better suggestion , some surplus or not retail - 9913 at the " best " price you can find , again best might get you a cheap manufacture and less quality .
    Here's a chart / not calculator , easier to go through type of spec. quicker .
    http://www.timesmicrowave.com/calcu...ency=10+MHz&runLength=300&mode=calculate#form
     
    KM6KRE likes this.
  3. N8AFT

    N8AFT Subscriber QRZ Page

    Open wire line is lowest loss HF.
    Doublet antenna design is historically the most efficient and it's easily tunable.
     
    2E0TWG, KD9CKB, AI3V and 1 other person like this.
  4. KM6KRE

    KM6KRE Ham Member QRZ Page

    Thank you for the feedback, I'm kind of a newbie and ever corner I turun, there's something new to learn. I'll look into the LMR 400 option.
     
  5. KM6KRE

    KM6KRE Ham Member QRZ Page

    Thank you!
     
  6. K7GQ

    K7GQ Subscriber QRZ Page

    Just wondering - are you intending on placing your antenna a little north of the basketball court in the trees?

    Usually, one end of an end-fed antenna is close to the shack or even in it. Running so much coax to an end-fed antenna doesn't make a lot of sense in that you'll have unusual impedances to match - not well suited for coax. In this hobby, almost all coax impedance is 50 Ohms and the antenna you're considering would not be a good fit.

    On the other hand, several companies make a multi-band dipole which should well be a close fit for a coax-fed antenna system.

    Good luck!
     
  7. KM6KRE

    KM6KRE Ham Member QRZ Page

    I had my eye on the trees! I'll consider a dipole instead. Still so much to learn with this hobby, had no idea when it first sparked my interests!
     
  8. K8ERV

    K8ERV Ham Member QRZ Page

    Not sure of it's power capacity but you might check the TV cable 75 ohm hardline, I think it is very low loss and may be available
    from cable company cheap or free.

    TOM K8ERV Montrose Colo
     
    KC8VWM likes this.
  9. AI3V

    AI3V Ham Member QRZ Page

    Well, I have worked with 6 1/8inch Hardline.

    Some thousand foot runs.

    They make even bigger stuff.

    Anyway, it's a question of how much you are spending to generate that 1500 watts, vs how much is lost in any given $ize of feedline.

    Strictly interperating the rules, you can have 1500w out of the amp.

    You could argue the spirit is 1500 at the antenna feedpoint, after all, you COULD install the final there.

    Also, there is the question of antenna gain vs power cost.

    And that antenna gain works double on receive, both a stronger signal, and possibly less noise.

    Rege
     
  10. K7TRF

    K7TRF Premium Subscriber QRZ Page

    As others have posted, as long as you have a fairly well matched antenna you'll be fine with LMR-400 or equivalent (e.g. RG-213) for a 250' to 300' run on the HF bands. Something like a set of parallel dipoles (aka fan dipole) fed with a single coax feed line or a multiband trapped vertical will satisfy the 'fairly well matched' condition. If you go with a non-resonant antenna like a G5RV or many end fed designs you may run into excessive coax losses on the bands where the antenna doesn't provide a decent match. IOW, if an antenna tuner in the shack is recommended for your chosen antenna design then it's not a great fit for your needs given your long coax run.

    The exception mentioned in a previous post is a multi-band doublet fed with balanced feed line. The big tradeoff here is that balanced feed line can be tough to run long distances. You can't bury it nor lay it on the ground and 250+ feet is a long horizontal run that would need off the ground supports along the way. But if you can work it out then yes, it's a very low loss way to run multiband operation out of a single wire antenna coupled to a good shack tuner.

    You can run coax on the ground or bury it if it's burial rated or if it's run through buried PVC or other conduit which can simplify your long horizontal coax run.

    Here's a decent coax loss calculator that can allow you to compare losses at different frequencies and different SWRs for transmission line runs of different lengths and for different cables: http://www.qsl.net/co8tw/Coax_Calculator.htm Note that the losses the calculator gives you are good first order estimates but not exact, still they're good enough for figuring out if you'd gain a lot with a different cable type or how high your SWR on the cable can get before losses become excessive.

    Remember to think in dB, not absolute watts. It may sound crazy to think about losing two hundred watts in your cable, but if that's 200w out of 1500w then it's only 0.6dB of cable loss. An S unit in ham radio terms is roughly 6dB and neither you nor the operator on the other end will be able to discern a signal strength change of 1/10th of an S unit. Neither we, nor radios hear in linear units so the difference you want to pay attention to is dB loss remembering it takes approximately 6dB of signal strength to make a single S unit change at either end of the radio link.

    So with 1500 watts out of your amplifier you could lose 3dB in your cable and your signal to the far end operator might change from 59 to 58. So don't go too crazy on trying to save every watt. All real world systems have some losses, try to contain them in a reasonable way but try to find a pragmatic balance between losses and overall system complexity and cost.
     
    KA0REN and KC9BNW like this.

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