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Old 16-05-2022, 06:37   #1
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General Radio/Ham cabling question for VHF

Since there's some really experienced and knowledgeable Hams here on Cruiser's Forum, I figured I'd get more trust-worthy, RF theory/science answers here than trusting some of the good ol' boys in my local Ham radio clubs....

Since, on higher frequencies like 144 and marine, it's preferable to use feedline like LMR400-type, how significant would be the effect of mixing different cabling, like 3ft RG8X, or a combination of available RG8X and LMR400 jumpers between equipment (tuner, SWR meter, radio)...fed by that primary run of LMR400, KMR400, etc ?

...any effects besides a little more loss ?
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Old 16-05-2022, 07:10   #2
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Re: General Radio/Ham cabling question for VHF

If you are keeping them short, like between devices such as SWR or Power Meter and radio, then it will be negligible. Because of turn radius and tight locations, it would benefit the use of smaller diameter cable like RG-58 or RG-174 in short runs. Just make sure you are using 50Ω cable so you have an impedance match.

Overall I would say don't make this molehill a mountain. Keep you runs short, maintain flexible cabling between devices and you should be fine.
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Old 16-05-2022, 07:15   #3
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Re: General Radio/Ham cabling question for VHF

The loss through good quality coax connectors is negligible. As long as the coax cables you mix are all 50 ohms, you are fine mixing them. Three feet is trivial.

It’s common for hams to mix cable sizes for interconnecting tuners, SWR meters, etc. when flexible cable is preferable but ‘harder’ thicker coax for long runs to towers where we again use more flexible cable which can tolerate movement as we turn antenna rotors.
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Old 16-05-2022, 08:50   #4
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Re: General Radio/Ham cabling question for VHF

Thanks....thought so, but had to ask, in case there was some odd real-world behavior I wasn't aware of at those freqs.

I have a spool of Ancor RG8X and Amphenol PL259's I can use to build a few more jumpers (for HF and VHF antenna interconnects with SWR meter, tuners, etc)....but when I went to the expense of 100' LMR400 feedline, couldn't help wondering if I was defeating it's purpose...

...but really didn't want semi-rigid solid-conductor jumpers either.
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Old 17-05-2022, 15:38   #5
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Re: General Radio/Ham cabling question for VHF

For HF you can use the RG-8X throughout. At those frequencies the loss is quite low.

For 2 meter (144) and marine VHF the losses are higher. Larger diameter coax it better.

LMR-400 is great coax but the conductors are aluminum. The center conductor is copper plated so you can solder the PL-259 to it but the shield can't be soldered. You need to use crimp connectors.

If you don't have the LMR-400 yet I suggest that you are better off with Marine grade RG-213. Besides being copper that can be soldered the dielectric is solid PE and the core is stranded making it more tolerable to bending than the foam/solid of LMR.
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Old 17-05-2022, 16:11   #6
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Re: General Radio/Ham cabling question for VHF

If you have access to a NanoVNA (not expensive) you can test the SWR of your cables easily with antenna attached or into a 50ohm load. I have a short blog post on this topic.
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Old 17-05-2022, 17:08   #7
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Smile Re: General Radio/Ham cabling question for VHF

Knowing practically nothing about electrical wiring, I was fortunate to have a marine electrician re-wire my boat including the ham station. Don't remember the size, but he used two-conductor cable the size of re-bar. He said when the mic is keyed the demand is much greater than the smaller (recommended) size wiring. It worked great because my signal was so strong I was occasionally asked to fill in as net controller. Hope this information will help.
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Old 18-05-2022, 07:15   #8
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Re: General Radio/Ham cabling question for VHF

You're talking VHF so don't sweat details about the cabling... really, what do you want to achieve anyway?
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