I have about 150 feet of LMR400 going to a tri-band 6m/2m/70cm antenna, and unfortunately the loss is quite high at these high frequencies, at this length. About 70 feet of that run is non-negotiable because that's how high the antenna is up in the tree. And then it's another 80 feet to my shack's entry point.

I'm wondering if I could replace the 70 feet of LMR400 that's going up to the antenna with 300 ohm window line I have available. Would that reduce loss? What would be the best way to do this (I'm assuming I need 4:1 or 9:1 baluns on both ends)?

Although the height is wonderful (I'm in a valley so it's pretty much required), the loss on the line making it very hard to hear/receive certain signals.

  • $\begingroup$ I'm thinking of doing exactly this for my 6m... the ladder line is not only lower loss but also lighter (with 50ft hanging from the antenna) and cheaper. $\endgroup$
    – user10489
    Sep 3, 2022 at 15:30

1 Answer 1


While maybe interesting on 6m (50 MHz), I'd expect the losses in twin-lead RF lines at 144 MHz and especially 400+ MHz (70cm) to be much higher. Honestly, twin-lead is really not made for anything that's beyond 100 MHz - the conductors are really (typically) just unbraided litz wire, which leads to a lot of conductive losses, and the fact that the geometry of window line is much less tightly definable than on coax means that at least to 70 cm, I'd expect some 30 m of twin-lead to look more like an antenna then a transmission line.

On the other hand, LMR-400 is a nice, low-loss medium. For 150 ft (my head sas that's 50 m in non-freedom units), I would expect some 4.4 dB in loss at 422 MHz – quite good, actually! For the 50 MHz (6m band) sine, I'd expect some, rule of thumb, 1.5 dB loss. So, while not zero, you'd need to do extremely well on the necessary matching, connection, weatherproofing and isolated mounting of the window line to not get more loss there than what you'd save at the low frequencies.

So, I'd just be happy about my (not really cheap!) LMR-400 line being in place, and I'd leave it untouched.

the loss on the line making it very hard to hear/receive certain signals.

I'd have my doubts: For microwave frequencies, i.e. > 300 MHz, we typically model noise to be dominated by 1. interference and 2. receiver noise. With narrowband receivers such as used by ham operators, the noise figures of receive amplifiers in that band should be low enough that losing a few dB on the cable doesn't matter – it does not make the interference-to-signal ratio worse, only the receiver-noise-to-signal ratio, and that's probably already not the problem.

For the 6m band, if I'm not mistaken, we model noise to be dominated by atmospheric noise, so that the cable loss doesn't matter at all! But I'm not an expert on these frequencies (they typically fall into what I'd usually call baseband…), so I'd have to defer to others there.

To know in what noise regime you are, maybe try with a low-power digital mode like FT-8 reception first. If that works well, you can use it to figure out whether your signal is actually close to the sensitivity of your receiver, or whether it's the interference that kills your reception. Good thing, that's probably "free to try", as you seem to have a computer!

Financially, trying with a slightly narrower preselection filter and an LNA might be cheaper than buying window line, cutting your expensive LMR-400, matching and connecting the window line and then, and that's the part where regrets happen if something goes wrong and water enters the coax, weatherproofing the connections. So, I'd start there!

  • $\begingroup$ Thank you, this is very helpful! I'm primarily interested in 6m at the moment, so I'll look more into the LNA and preselector configuration you mentioned, as that's new to me. Appreciate it! $\endgroup$ Sep 1, 2022 at 14:32
  • $\begingroup$ I agree, even at 70cm, if you lose more than a couple db, the problem isn't the type of cable, it's the cable itself (or a bad connector.) $\endgroup$
    – Duston
    Sep 1, 2022 at 14:42
  • $\begingroup$ @Duston I'm sorry, I don't quite understand "the problem isn't the type of cable, it's the cable itself", could you elaborate? $\endgroup$ Sep 1, 2022 at 15:37
  • $\begingroup$ What I mean is that LMR400 in general is good cable and wouldn't suffer that kind of loss. That particular piece of LMR400 that you have does not appear to be up to the specs of what LMR400 should be. $\endgroup$
    – Duston
    Sep 2, 2022 at 12:27
  • $\begingroup$ @Duston ah! Makes sense! Though we don't actually have measurements of it? $\endgroup$ Sep 2, 2022 at 14:57

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