Hey everyone,I wanted to know if I would have great transmiting loss on a 70 foot long coax run? What would be a good coax for that long of a run? Would a 5 watts output be lost quickly on that long of a run?
Coxial question
- Thread starter Rt169Radio
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n5ims
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For most types of coax (the cheap brands excluded), a 70 foot run will work fine on HF, even with less than 5 watts. RG-58 would be fine, RG-8X (aka mini-8) would be better, and the larger RG-8 even better (especially as you increase your power). I'd stay away from low quality cable, but mostly for the uneven shielding and other qualities that make it low quality. I would also avoid RG-174, because it's simply too small to work with easily and connectors are hard to find for it.
As you increase in frequency, the type (and quality) of coax gets quite important. What works fine on the lower frequencies may work really poorly as the frequency increases. For VHF-Hi (2 meters for hams) I'd avoid using RG-58 or RG-8X for runs of any real length (they're OK for short patch cables or mobile use however). The various RG-8 flavors will work fine however (remember that RG-8X isn't the same thing as RG-8, although the name looks similar, the performance isn't anywhere near the same!). These include RG-213, RG-214, Belden 9913, LMR-400, etc.
For UHF (the 440 or 70 cm band) RG-8 would be the minimum level to start with with the lower loss versions generally worth the extra cost. You may even want to consider the commercial grade heliax like Andrew LDF4-50A or something larger than RG-8 like LMR-600. Please note that the heliax can be expensive, but you can often find folks selling short runs (end-of-reel type things) for about what a dealer will charge for LMR-400 and get much lower loss and better life out of the coax.
Use a coax loss calculator (Welcome to Times Microwave | Coaxial Cable - Attenuation & Power Handling Calculator) and your dealer's on-line price chart as a guide to find what works best for you price vs performance wise. And above all, stick with quality coax!
As you increase in frequency, the type (and quality) of coax gets quite important. What works fine on the lower frequencies may work really poorly as the frequency increases. For VHF-Hi (2 meters for hams) I'd avoid using RG-58 or RG-8X for runs of any real length (they're OK for short patch cables or mobile use however). The various RG-8 flavors will work fine however (remember that RG-8X isn't the same thing as RG-8, although the name looks similar, the performance isn't anywhere near the same!). These include RG-213, RG-214, Belden 9913, LMR-400, etc.
For UHF (the 440 or 70 cm band) RG-8 would be the minimum level to start with with the lower loss versions generally worth the extra cost. You may even want to consider the commercial grade heliax like Andrew LDF4-50A or something larger than RG-8 like LMR-600. Please note that the heliax can be expensive, but you can often find folks selling short runs (end-of-reel type things) for about what a dealer will charge for LMR-400 and get much lower loss and better life out of the coax.
Use a coax loss calculator (Welcome to Times Microwave | Coaxial Cable - Attenuation & Power Handling Calculator) and your dealer's on-line price chart as a guide to find what works best for you price vs performance wise. And above all, stick with quality coax!
Where would I get some RG-8 coax?
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