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My question is specifically regarding using a homemade twisted pair of 14 AWG XHHW-2 wires as twin lead feedline for high-power HF ham transmissions. A somewhat similar question has been posted in the community (and answered) regarding the use of twisted pairs as found in CAT5 cable for lower-power transmission line, but I'm specifically asking about using 14 AWG XHHW-2 wires, not the flimsy wires typically found bundled as 4 twisted pairs in CAT communications cable. I'm intrigued with the concept of using 14 AWG XHHW-2 twisted-pair as high-power feed line because of its relative ease of construction, relative ease of routing between my amplifier and antenna, and (hopefully) improved power loss compared to coax.

So, what are the disadvantages (if any) of using twisted-pair 14 AWG XWWH-2 wire feed line vs traditional ladderline for high power transmission line?

Thanks in advance, Mark

Mark K1LSB
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  • 12 gauge is good for 30A. Legal limit is likely a lot more than 30A and 14 gauge is marginal for even 100w. – user10489 Jan 16 '24 at 12:32
  • the problem here is that a) all your losses are in the dielectric. I don't think dielectric of XHHW wires is going to be low-loss material, so no, you can't. and b) you simply won't produce a very reliable-impedance line. So, I'll go with "no, you can't, practically. This will be a very lossy and leaky line, rendering it so bad that you won't want to use it.". – Marcus Müller Jan 16 '24 at 20:05
  • Anyway, this question simply is factually impossible to answer - your specific cable in the way you built it, at your specific installation geometry and at your temperature would need to be checked with a network analyzer. twisted pair isn't consistent enough to make general statements (which is also why it's not great feed line) – Marcus Müller Jan 16 '24 at 20:07
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    The (previously) linked answer (mine) still answers this question almost exactly. Expected impedance. Concerns about losses. Comparison to 300 ohm twin line. Suggestions for how to test the insulation. The only difference is that the impedance may be a bit lower, 110-120 ohms because the wires are a bit closer together. I still don't recommend it, especially for a kilowatt, what you could use instead is a 300-450 ohm ladder line with home-made spacers. – tomnexus Jan 16 '24 at 20:40
  • Tom, I did thoroughly read your (previously) linked answer back when you posted in the original thread, thank you very much. Your comments regarding the PVC insulation on the UF-B wire were in fact what prompted me to ask about XHHW-2 this time. XHHW-2 uses cross-linked polyethylene (XLPE) for insulation, which has a dielectric constant of 2.2, very close to that of Teflon. So I was hoping that losses would be low. – Mark K1LSB Jan 17 '24 at 15:35
  • And regarding the feedline impedance of twisted pair being on the low side, I don't understand how that would really matter, given that many hams are using everything from 300 ohm to 600 ohm ladderline for feedline, and the specific impedance they select is of little consequence in the final circuit, assuming their matching transformer (tuner) is able to accommodate that impedance. So where am I mistaken in my thinking? – Mark K1LSB Jan 17 '24 at 15:35
  • Tom, I was also wondering about your suggestion of simply using a pair of RG-6 cables as balanced lines and grounding the shields....wouldn't the losses in that setup basically be the same as simply using a single RG-6 cable as coax? – Mark K1LSB Jan 17 '24 at 15:36
  • Marcus, what is low-loss insulation if Teflon is not? Cross-linked polyethylene (XLPE) has a dielectric constant of 2.2, very close to that of Teflon (2.1). – Mark K1LSB Jan 17 '24 at 16:22
  • @MarkK1LSB that's the real part of the dielectric constant, or its magnitude; what you care about for losses is the imaginary part; that's often encoded in data sheets as loss angle $\tan \delta$. You're generally right, teflon modifications tend to be on the lower loss side of things, but XLPE isn't similar to Teflon; typical XLPE has an $\varepsilon_r$ of ca 2.8 to 2.9, with $\tan \delta \approx 10^{-2}$ – Marcus Müller Jan 17 '24 at 18:06
  • Thank you Marcus, that's over my head but good info. So my next question is, would similar losses apply if I were to construct a 450 or 600 ohm ladderline using 14AWG XHHW-2 (compared to the losses in a twisted pair with the same wire)? In other words, I still don't understand where the losses occur. And would it still matter what particular insulation I used if I were building ladderline instead of a twisted pair? If not, then why would insulation material matter in a twisted pair but not in a ladderline? Sorry for the endless questions but I'm trying to understand. – Mark K1LSB Jan 17 '24 at 19:03
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    @MarkK1LSB maybe ask that in a new question, titled something like "ladder line vs twisted pair: where do the losses actually occur?" or so? – really not Constantine A. B. Jan 18 '24 at 09:07

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