Recommended Coax for 800W HF Linear Amp?

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This topic contains 2 replies, has 2 voices, and was last updated by Fred Kemmerer Fred Kemmerer 1 year, 11 months ago.

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  • #2960
    Fred Kemmerer
    Fred Kemmerer
    Keymaster

    What would be a recommended coax for use with an 800W HF Linear amplifier to antenna?

    - Fred (AB1OC)
    President, Nashua Area Radio Society

    ab1oc@arrl.net
    Visit us on the web at - https://www.n1fd.org

    #2962

    Hamilton
    Participant

    I like LMR-40o. It is not the least expensive but it is reasonable given the performance.

    Times has a nice calculator at http://www.timesmicrowave.com/calculator/?productId=52#form  You can compare a wide range of cables.

    It shows LMR-400 at 2.47 kW average at 54 MHz and 0.9 dB per 100 ft. LMR-240 is 1.11 kW average and 1.8dB per 100 ft. Power handling drops with increasing frequency and loss goes up making 6 meters a good comparison point.

    There are a lot of knock off cables out there with “400” in the part number. Some approach LMR-400 at less cost while many are cheap cables trading on the Times brand.

    73

    Hamilton

    Hamilton (K1HMS)
    Amherst, NH

    #2963
    Fred Kemmerer
    Fred Kemmerer
    Keymaster

    Hamilton’s advise is sound here. LMR-400 is a good choice for any HF application requiring power handling. When selecting coax, the following considerations should apply:

    1) What is the maximum frequency that the coax will be used at? Loss related factors will increase with frequency.

    2)What is the total length and how much loss does a given coax have at the desired length? I generally engineer my feedline systems to have no more than 1 dB of loss from the feedpoint of the antenna to the back of the transceiver.

    3) What is the likely maximum SWR that the system will be operated at? If you will be operating at SWRs of 2:1 or higher, the additional losses due to the higher SWR as we as the associated higher power levels generated on the coax need to be considered. There are several loss calculators online that will do these calculations for you. You can find one here.

    4) Given the intended power levels and the associated increases in power due to SWR above 2:1, choose a coax that can handle the desired power. Its best to consult the manufacturer’s specification sheet for the coax that you have in mind to determine the power handling capability of the coax you are considering. Note that power handling capability will also depend upon the maximum frequency that the coax will be operated at.

    5) There are some considerations depending upon how you will mount your coax. For example, if you intend to direct bury you coax, you will need a coax cable that is designed of direct burial.

    LMR-400 coax is generally a good choice for most high-power HF and 6m (up to 50 MHz) applications for lengths up to 150 ft or so. You can see the specifications for LMR-400 here.

    73,

    - Fred (AB1OC)
    President, Nashua Area Radio Society

    ab1oc@arrl.net
    Visit us on the web at - https://www.n1fd.org

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