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What is an acceptable loss for you for your coax on the HF frequencies?

Discussion in 'Ham Radio Discussions' started by KN4DQE, Nov 6, 2018.

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  1. KY5U

    KY5U Subscriber QRZ Page

    He’s runnin’ barefoot. What was your handle on CB? :):) Seriously check your figures. Cable loss is more like .3 db on 28mhz. Lower on lower bands.
     
    Last edited: Nov 7, 2018
  2. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I do that but sometimes I get dizzy, hanging from the boom of my beam on the tower.

    Plus it gets lonely.
     
    N0TZU likes this.
  3. K4KYV

    K4KYV Subscriber QRZ Page

    Or use open-wire line. The real thing, with copper wires separated by plastic or ceramic spacers every few feet, not that "crappy brown stuff". The run from my shack to the final stage of the transmitter tuning network located down at the base of the tower is about 140 feet. I tried fresh mil-spec coax, first RG-214, then RG-213. In both cases, the measured efficiency was about 92%. After a couple of years of exposure to the elements, in both cases the efficiency dropped off to around 80%. Then I replaced the coax with a run of homebrew open wire line, 440Ω, made with #8 wires spaced 2 ½ inches apart, and the measured efficiency was 98%.

    Probably none of those made a perceptible difference in the received signal at the other end, but I still think RF is too difficult and expensive to generate, and then waste in feedline losses.
     
    KN4DQE and KC8VWM like this.
  4. KC8VWM

    KC8VWM Moderator Volunteer Moderator QRZ Page

    Well I think you must be doing something right... At least my s-meter always thinks so anyways. :)
     
  5. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    If I turn my RF gain down enough, everyone is 40/S9.:)
     
    N0TZU, NL7W, WZ7U and 2 others like this.
  6. KK5JY

    KK5JY Ham Member QRZ Page

    ...and all the atmospheric noise just vanishes... :eek:
     
  7. KA2RRK

    KA2RRK Platinum Subscriber Platinum Subscriber QRZ Page

    Are you hooked to 120vac? Cuz, the AL-80B easily gets to 1kw.

    This your enemy, do something to lower these figures. I'm not really upset about these figures, but in my
    station I consider anything above 1:2.0:1 vswr out specification for high power use. High power is anything above
    50watts.

    LMR-400 abbreviated specs:
    @.7db loss per 100ft measured @30mhz That's excellent for HF service.
    @ 2500v rated handling I'd say you have little worry running the most power you can muster from the amp,
    Along with it's .1" diameter center conductor size.

    Now these later numbers from times micro are better than what you have! Because you are not terminated
    into a matched load the cable desires to perform at low loss. So if you actually measure your losses you probably are at 2db or slightly more, is my guess. And I wouldn't use the amp until this issue is addressed fully.


    KA2RRK
     
  8. W5TTW

    W5TTW Platinum Subscriber Platinum Subscriber QRZ Page

    Two questions:
    1. Have you considered switching to ladder line?
    2. Where will you put your tuner?
     
  9. KA9JLM

    KA9JLM Ham Member QRZ Page

    Yep. That is what these are made for.

    upload_2018-11-7_19-48-9.jpeg
     
    NL7W, K2XT, WZ7U and 2 others like this.
  10. KN4DQE

    KN4DQE Ham Member QRZ Page

    Ladder line could work up to a certain point. I hadn't considered that. Was just looking at coax due to ease of use. I was reading that I shouldn't because l necessarily need a tuner since the amp itself acts like one in a way. If I werewe're g to get one I was looking at the mfj-998rt, but that is a lot of money, especially when compared to replacing the coax.
     

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