Looking for Coax Recommendations

Discussion in 'Satellite and Space Communications' started by KF0FQL, Sep 16, 2021.

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  1. K7WDO

    K7WDO Ham Member QRZ Page

    If you've ever seen the center conductor on LMR400, you'll understand why it's a bit on the stiff side. The big difference between the normal and UF versions of LMR is the standard version uses a solid center conductor while the UF is stranded. This lets it stand up to repeated flexing and tighter bends that might cause a solid center to break. It's still a thick, heavy cable so great for fixed installations, but a little heavy for portable ops.
    As for the comment on LMR400 not being as good for VHF, it's more a case of coax tends to have higher loss per foot as the frequency increases so using a higher grade coax like LMR400 or 9913F7 for UHF will show a more noticeable improvement than with lower frequencies. It works equally as well with VHF, but you just won't think you're getting as much bang for the buck compared to a lighter (cheaper) grade of coax.
  2. AI5DH

    AI5DH Ham Member

    If you use the UF version you give up the low loss. You defeat the purpose.
  3. K7WDO

    K7WDO Ham Member QRZ Page

    As in engineering, there are always compromises and you do lose a little performance between the regular and UF versions, but it's not horribly bad (0.3 to 1 dB per 100 feet). It's still a pretty good trade off if the coax is going to be flexed on a regular basis like in portable operations or a rotor loop.

    From the specs:
    Coax (type) dB Loss per 100 feet (2m/70cm)
    Belden 8240 (RG-58) 3.8 / 8.4
    Belden 9258 (RG-8x) 3.1 / 6.6
    LMR-240 (.24”) 3.0 / 5.3
    LMR-240UF (.24”) 3.6 / 6.3
    LMR-400 (RG-8) 1.5 / 2.7
    LMR-400UF (RG-8) 1.8 / 3.3
    Belden 9913F7 (RG-8) 1.5 / 3.0

    Note: Belden quotes loss at 100 MHz & 400 MHz, Times Microwave quotes it at 150 MHz & 450 MHz so don't read too much into that 0.3 dB difference between LMR400UF and 9913F7. See https://catalog.belden.com and https://www.timesmicrowave.com
  4. AI5DH

    AI5DH Ham Member

    I am a train driver, and that was my point. Using the numbers you provided, LMR-240 UF has roughly the same loss as the RG-58. No gain realized with the upgrade.

    It's a moot point because the coax length in question is 10-feet. That short of coax length does not matter what type it is; the losses will be minimal. Use what you got is more than good enough, and if you need to purchase, purchase what will fit most all your applications. The application being satellite, the most critical factor is the receiver noise factor.
  5. N4UFO

    N4UFO Ham Member QRZ Page

    How exactly do you figure that???

    Attenuation dB/100 ft

    RG-58 10.6 db @ 450 MHz (generalized coax chart)
    RG-58 low loss 7.8 db @ 450 MHz (pasternack)
    LMR-240 5.3 dB @ 450 Mhz (pasternack)
    LMR-240UF 6.3 db @ 450 MHz (pasternack)
    CQ118 6.2 db @ 440 MHz (wireman)

    Difference between RG-58 and LMR-240 UF is over 4 dB. (still 1.5 dB over the RG-58 low loss), but only 1 db more than the regular LMR-240. I calculate over 4db gain there over RG-58. I hardly call 4 dB difference 'roughly the same loss'.

    Minimal or not, real world usage with satellites tells experienced ops that the difference is significant enough and that coax type does matter. So-50 satellite is transmitting 250 mW to a 1/4 chassis mounted quarter wave whip from over 400 miles up moving at about 4.5 miles per second. Trust me... even with a few feet of coax it CAN matter. (at 10 feet LMR-240UF is 0.43 db less loss than RG-58) Same argument as removing a few feet of coax... some say it doesn't matter, but it does. I've seen it, ops I know have seen it, published ham experimenters have seen it.

    Quoted from: https://www.jerryclement.ca/MachineShop/Antenna-Werks/i-sNNxBCL

    "However, when using the CJU antenna with a length of coax connected to my Yaesu FT-817ND, I noticed some loss in the signal. To rectify the problem, I mounted the antenna on a Advanced Receiver Research preamplifier with included handle. Now, I can work the satellites right on the horizon and the modified antenna looks kinda cool besides."

    Huh, published ham... added a few feet of coax and noticed enough difference to add a preamp. Who'da thunk it?
    Last edited: Sep 18, 2021
    N5WTF, KS1G, KB1PVH and 2 others like this.
  6. K3RLD

    K3RLD Ham Member QRZ Page

    Regarding LMR400UF, I've attempted to use it and find that it is practically unusable as a portable coax. Sure, it's more flexible than true rigid coax, but not by much. :)

    If you are going to go with LMR_UF for portable usage, the 240 is really the only option.
    KS1G likes this.

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