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Old 03-12-2020, 23:49   #1
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Which coax cable for HF radio to tuner?

Which coax cable should I use to connect my radio to the antenna tuner ~ 25' away? I looked at the coax attenuation calculator (https://www.qsl.net/co8tw/Coax_Calculator.htm) plugging in 14MHz and it looks like there's very little loss difference between RG58, RG59, and RG8X. Do I let color and cost become the determining factors or is there some other factor I need to consider?
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Old 04-12-2020, 00:17   #2
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Re: Which coax cable for HF radio to tuner?

If cost is not a factor I would highly recommend LMR-400 UF as it is less lossy than the RG cables. For marine SSB/Ham I recommend optimizing as much as possible.

See https://www.w4rp.com/ref/coax.html
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Old 04-12-2020, 00:47   #3
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Re: Which coax cable for HF radio to tuner?

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Originally Posted by Discovery 15797 View Post
If cost is not a factor I would highly recommend LMR-400 UF as it is less lossy than the RG cables. For marine SSB/Ham I recommend optimizing as much as possible.

See https://www.w4rp.com/ref/coax.html
That does look like a better cable. Unfortunately, it may not be available where I am (Langkawi, Malaysia). I may have to wait until I get back to Europe or the US to consider it.
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Old 04-12-2020, 05:03   #4
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Re: Which coax cable for HF radio to tuner?

Rg8x or 213.

58 or 59. (One if those is 75ohm tv cable and not correct, always mix which is which ). Is junk.
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Old 04-12-2020, 07:02   #5
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Re: Which coax cable for HF radio to tuner?

At 14MHz for 25 ft, the loss difference is trivial. Even at VHF, it isn’t a big difference for short lengths.
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Old 04-12-2020, 08:58   #6
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Re: Which coax cable for HF radio to tuner?

Loss is not ordinarily a factor for short runs at HF. You would choose a cable that is:
* Readily available, including suitable connectors

* Flexible
* Durable in a marine environment

* 50 ohms characteristic impedance

* Able to handle the power.


Ordinarily RG8 or RG213 would be used. They are reasonably flexible (though not as flexible as RG58 or RG8X) and perform well in a variety of environments. They're inexpensive. PL259 connectors for them are readily available. There is little difference between RG8 and RG213 at HF.


RG58 is marginal for the amount of power involved but will probably work OK as long as your tuner, antenna, and ground are good. Intermittent connections in these systems can reflect enough instantaneous power back towards the transmitter to damage RG58 though.


I wouldn't use LMR400 for several reasons. It has an aluminum foil inner shield that is more prone to corrosion than braid in marine environments. It also uses a foam dielectric that can lose its shape in high-temperature environments where there are tight bends or pressure on the cable.


RG8X has a foam dielectric also though the shield is copper braid. No real benefit for a short run where there's plenty of room -- the advantage over RG8 is that it's small and light.
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Old 04-12-2020, 12:43   #7
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Re: Which coax cable for HF radio to tuner?

If you wish to minimize loss /maximize transmission the use of PL-259 connectors is not recommended because they do not have a stable, defined impedance. This means some energy in the line is reflected back toward the source, causing loss. While this is not a major issue at frequencies of 30 MHz and below it is not good practice. I suggest using type N connectors where you have a choice or TNC for smaller, low power connections. Unfortunately, much HF equipment including antennas use PL-259 connectors which renders much of what I have stated moot.
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Old 04-12-2020, 14:25   #8
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Re: Which coax cable for HF radio to tuner?

Twenty-five feet of RG58 is just fine. The loss at 14MHz is only half a decibel, which is virtually undetectable. Just make sure you use the RG58 with a stranded inner conductor—a solid inner conductor will work-harden with the inevitable vibration in a boat, and will then crack or break.

RG59 is the wrong impedance (75 ohms instead of the required 50). AVOID.

Yes, the PL259/SO239 combination is sub-optimal, but every HF radio and tuner I have ever seen (and in 56 years of installing radios I have seen rather a lot) has been fitted with SO239 antenna sockets. At HF they perform adequately, and it is just not worth the trouble of replacing them. (And if the OP knew how to do that, he would not have started this thread!)

As this co-ax is to go between the radio and the tuner, the radio is unlikely to see any high SWR, so the idea that the RG58 might break down from over-voltage is highly unlikely. Besides, even a high SWR from the usual 100 watts is unlikely to be anywhere near RG58's break-down voltage. RG58 is rated to 800 watts in the real world.
So have at it, Epicurean. RG58 is your go-to coax for HF.
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Old 04-12-2020, 14:51   #9
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Re: Which coax cable for HF radio to tuner?

Quote:
Originally Posted by thunderhoof View Post
If you wish to minimize loss /maximize transmission the use of PL-259 connectors is not recommended because they do not have a stable, defined impedance. This means some energy in the line is reflected back toward the source, causing loss. While this is not a major issue at frequencies of 30 MHz and below it is not good practice. I suggest using type N connectors where you have a choice or TNC for smaller, low power connections. Unfortunately, much HF equipment including antennas use PL-259 connectors which renders much of what I have stated moot.

He's connecting two pieces of equipment that have SO-239s on them.
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Old 04-12-2020, 16:00   #10
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Re: Which coax cable for HF radio to tuner?

Stranded core as mentioned previously and I would recommend tinned braid versus the regular copper wire shield. I’m not sure if double braid is available with RG58 but if it is a option, I would also buy that. RG8X works great as mentioned but I would opt for tinned braid on it if available.
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Old 06-12-2020, 06:57   #11
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Re: Which coax cable for HF radio to tuner?

Thanks for all the advice. Now I just have to see what is actually available here (Langkawi, Malaysia).
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Old 06-12-2020, 15:52   #12
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Re: Which coax cable for HF radio to tuner?

In Malaysia you should be able to score loads of RG213, RG8X, maybe even LMR240. Both will work fine. Stick with standard: PL259. If you equipment came with N or TNC or 50Ω BNC, then yeah, go with those. Otherwise, PL259 is good enough.
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Old 06-12-2020, 16:07   #13
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Re: Which coax cable for HF radio to tuner?

FYI...I also would not recommend LMR-400 with a solid center conductor for marine installs. That is why I specifically stated LMR-400 UF (ultra-flex) that has a stranded center conductor.

If the aluminum 2nd shield on LMR cable corrodes it would likely be due to an incorrectly installed connector; which would also corrode the braid.

But, as others have suggested...at this length and frequencies the difference in cables is pretty insignificant...so use a 50 ohm cable that is readily available to you and install the connectors that match the equipment (probably PL-259s).
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Old 07-12-2020, 04:38   #14
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Re: Which coax cable for HF radio to tuner?

I recommend RG-8/U cable with PL-259 connectors.
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