Off Topic RG-174
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Will RG-174 handle 100W at HF/6M?
I am building a tuning bridge for my Nye Viking tuner, and will be installing a relay to switch it in and out of circuit. My K3 will transmit and receive through the NC contacts of the relay. Mike Mike Short AI4NS [hidden email] _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Mike,
My chart in the ARRL Handbook says RG-174 has a dielectric breakdown voltage of 300 volts RMS. So in theory, it will handle 1800 watts at an SWR = 1.0 (less at higher SWR) - but I would not trust it at much over 25 watts myself. I like to see a larger safety factor where transmission lines are concerned. The ohmic losses may be great too, that all depends on the length and the SWR. 73, Don W3FPR Mike Short wrote: > Will RG-174 handle 100W at HF/6M? > I am building a tuning bridge for my Nye Viking tuner, and will be > installing a relay to switch it in and out of circuit. > My K3 will transmit and receive through the NC contacts of the relay. > > Mike > > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Well, that shows that it ought to be OK from the voltage breakdown
perspective, but consider current carrying capability or self heating of that little bitty center conductor too. It might be limiting. If you allow it an amp, 50 watts. Two amps, 200 watts. At 100 watts of course, 1.414 amps. Probably OK, I'd think. But I don't know that I'd go much higher. 73--Nick, WA5BDU Don Wilhelm wrote: > Mike, > > My chart in the ARRL Handbook says RG-174 has a dielectric breakdown > voltage of 300 volts RMS. So in theory, it will handle 1800 watts at > an SWR = 1.0 (less at higher SWR) - but I would not trust it at much > over 25 watts myself. I like to see a larger safety factor where > transmission lines are concerned. The ohmic losses may be great too, > that all depends on the length and the SWR. > > 73, > Don W3FPR _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Well, according to the wire tables, the 26 gauge center conductor can safely handle about 350 to 400 milliamperes, depending on how you interpret the safety factors. The center conductor is certainly not operating in "open air", so the best figure is probably the one used for wire in bundles. That works out to 10 watts or thereabouts, which strikes me as about right for RG-174. Give or take a little room for SWR, this sounds like a safe "rule of thumb" for normal use. At 1800 watts, I would stand waaaay back when power was applied! Can you say "BOOOM" ? - Jim, KL7CC Nick-WA5BDU wrote: > Well, that shows that it ought to be OK from the voltage breakdown > perspective, but consider current carrying capability or self heating > of that little bitty center conductor too. It might be limiting. > > If you allow it an amp, 50 watts. Two amps, 200 watts. At 100 watts > of course, 1.414 amps. Probably OK, I'd think. But I don't know that > I'd go much higher. > > 73--Nick, WA5BDU > > > Don Wilhelm wrote: >> Mike, >> >> My chart in the ARRL Handbook says RG-174 has a dielectric breakdown >> voltage of 300 volts RMS. So in theory, it will handle 1800 watts at >> an SWR = 1.0 (less at higher SWR) - but I would not trust it at much >> over 25 watts myself. I like to see a larger safety factor where >> transmission lines are concerned. The ohmic losses may be great too, >> that all depends on the length and the SWR. >> >> 73, >> Don W3FPR > > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > > Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Mike Short
At 06:33 PM 7/26/2008, Mike Short wrote...
>Will RG-174 handle 100W at HF/6M? Maybe. RG-188A/U (Belden 83269) might be a bit better, it's rated for much higher temperatures (to 200C), and has slightly less loss (vs. Belden 8216 RG-174/U). http://www.belden.com/pdfs/03Belden_Master_Catalog/06Coaxial_Cables/06Coaxial_Cables.pdf There's this: http://www.therfc.com/powerrat.htm#RG174 Says 174 is good to 160W@50MHz and 188 to 480W@50MHz Then this: www.qsl.net/va3iul/coaxloss.pdf Says 174 is good to 95W@145MHz and 188 to 380W@145MHz The two sources roughly agree. I assume that they assume a 1:1 SWR. _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Mike Short
Mike Short wrote:
> Will RG-174 handle 100W at HF/6M? > > For the reasons given in other posts, I wouldn't trust it. One thing I've seen with RG174 is migration of the center conductor caused by I^2R heating where the cable is bent into a small radius. It does not take much shift to cause a center conductor-to-braid short. If you have to use a small diameter cable because of physical limitations, I would go with a Teflon equivalent, such as RG-188. Jack K8ZOA www.cliftonlaboratories.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Jim Wiley-2
Jim Wiley wrote:
> > Well, according to the wire tables, the 26 gauge center conductor can Where do you find wire tables for 50MHz? The ones I've seen are for 50 or 60Hz. > safely handle about 350 to 400 milliamperes, depending on how you If you are using 60Hz wire tables, you will need to derate the current handling by maybe a couple of orders of magnitude! I'd suggest finding out the mains frequency resistance, then calculating the power dissipation per unit length. Next take the 50MHz attenuation and convert that to a power dissipation, and match the two. This is not perfect, because the attenuation will include dissipation in the dielectric and the shield, which might be closer to the surface and therefore dissipate more easily. -- David Woolley "The Elecraft list is a forum for the discussion of topics related to Elecraft products and more general topics related ham radio" List Guidelines <http://www.elecraft.com/elecraft_list_guidelines.htm> _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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