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I've done outdoor activities, POTA and WWFF, with a coax RG58 feed line with PL conectors, around 3 meters (9.8 feets), for wire EFHW antennas working HF bands (40m, 20m and 10m).

Now I want to do SOTA, and it implies to climb a summit, so the weight in my backpack is an issue. I need a more long feed line, round 7 meters (23 feets), with BNC connectors. I'm thinking to make with coax RG174 but I'm afraid from the losses.

The power output of my rig is in the range 0.4w-5w.

What tipe of coax is better for this compromise use between lightweight and low losses?

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Plenty of SOTA activators use RG-174. Being on top of a mountain more than compensates for losses in transmit power. Being in a low RF noise location more than compensates for any receive losses.

One S-Unit is 6 dB, so even that much loss often is not noticeable.

SOTAbeams in the UK sells both RG-58 and RG-174. Either one can be a good choice. https://www.sotabeams.co.uk/co-axial-and-patch-cables/

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  • $\begingroup$ just to put attenuation into relation: typical RG-174 is spec'ed for much higher frequencies than what hams consider "HF bands", so it's even hard to find losses this far down in frequency; they'll be lower than what the cable datasheet (buy cable with datasheets!) says for 100 MHz. And Pasternack and similar higher-end suppliers specify that their RG-174 loses 27.56 dB/100m, or 0.2756 dB/m (yes, that's how the math works out), so you lose less than 2 dB in a 7m long cable. Unless you have phenomenal crimping abilities and phenomenal connectors, $\endgroup$
    – Marcus Müller
    Commented Mar 23 at 16:30
  • $\begingroup$ I wouldn't be convinced that cable losses matter more than connector losses - and you can't avoid these. So, relax and use any cable of the right impedance, be it RG-174, RG-58, or whatever your supplier has at hand, and for which you can specifically find BNC connectors!. Don't buy stuff that might have sat in wet environments for long (the typical "suspiciously cheap flea market cable drum"), as that might actually make a difference. $\endgroup$
    – Marcus Müller
    Commented Mar 23 at 16:33
  • $\begingroup$ And RG-174 is an excellent example of a cheap, reliably sourcable, well-supported coax type; BNC connectors for RG-174 tend to be a few Euros more expensive than such for RG-58, so balance cable and connector cost. $\endgroup$
    – Marcus Müller
    Commented Mar 23 at 16:41
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    $\begingroup$ Checking 23 feet of RG-174 at 14 MHz, I get 0.7 dB loss. RG-58 is about half that. So totally negligible. Even with 3:1 SWR, the RG-174 has 1 dB of loss. qsl.net/co8tw/Coax_Calculator.htm $\endgroup$
    – Walter Underwood K6WRU
    Commented Mar 24 at 17:07
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    $\begingroup$ Crimping losses can happen regardless of the type of coax, so that isn't a reason to stay away from RG-174. It is probably a reason to use professionally-installed connectors. $\endgroup$
    – Walter Underwood K6WRU
    Commented Mar 25 at 18:11
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You can't have your cake and eat it. Lightweight coax is smaller coax, and smaller coax has higher losses. Size (diameter), operating frequency, and loss are directly proportional. No one can answer your question except you. You have to decide how much weight and insertion loss you can afford.

For example, professionals aim to limit insertion losses to 2 dB or less. Say the feed line is 25 feet long and operates at 14.0 MHz. What coax is appropriate? RG174 = .8dB loss. RG58 = .5dB. Either works well.

Up the frequency to 144 MHz and RG174 = 2.8 dB (unacceptable) and RG58 = 1.8 dB, not great but doable. Go up to 450MHz, and both fail. RG174 = 5.3dB and RG58= 3.5 dB.

Go figure out what you need. I would use LCF158-JA. But that is just me.

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  • $\begingroup$ Heh. LCF158-JA IS ~1kg/m. If mass is a primary driver for choice, then losses will be had. This stuff looks nice, though. $\endgroup$
    – user26657
    Commented Mar 22 at 19:48
  • $\begingroup$ Well, it is a 1-5/8-inch hard line. At 25 feet, the loss is so low that it cannot be measured accurately. LOL $\endgroup$
    – user23405
    Commented Mar 22 at 20:33
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    $\begingroup$ yeah, that's the stuff you install between your radio unit at the foot of a tall tower, and the antenna, where power matters. Don't fully agree with "can't be measured", but "can't be measured with any effort that stands in any sensible relation to the application field here" :D Pretty sure though that there's realistically better trade-offs between portability and loss than this, but as you say: the highest band they want to work is 28 MHz, so: it really won't matter. Worry about the quality of your crimps, and the quality of your antenna matching, if you want something to worry about. $\endgroup$
    – Marcus Müller
    Commented Mar 23 at 16:51
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    $\begingroup$ @MarcusMüller yup, with most modern rigs make the effort to match as best you can, and losses aren't what are going to keep you from making contacts. $\endgroup$
    – user26657
    Commented Mar 25 at 13:33
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Good RG58 is typically 40g/m or less. Is that mass too much compared to the mass of the radio and batteries?

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