Okey, folks. Thanks for all the good input. Responding to several posted queries, I've gathered additional information:
1. I peeled away a sliver of the outer rubber insulation to inspect the shield. It's tinned copper braid over foil, which could be any of a number of RG-8 family cables. 2. Connecting the SWR/wattmeter at the "far" end of the cable shows that transmission loss is miniscule; at both 6 meters and 10 meters, I can't discern a difference in the needle position on the SWR/wattmeter. On 10 meters is's 12 watts. On 6 meters it's about 8.8, which is all that the K3 puts out on 6 meters. 3. SWR is 1.05:1 on 10 meters, and 1.5:1 on 6 meters, but I think this is the dummy load, not the coax. I get the same readings when I connect the dummy load to the wattmeter with a three foot section of Cable X-pert RG-8 foam insulation cable. 4. I'm pretty sure it's not RG-9, as someone suggested. Both the diameter and the capacitance per foot are much more in the RG-8 family than RG-9 (spec. .420 diameter, vs. measured .405 which is right on target for RG-8, and capacitnce of 23.1 pF per foot, vs. specified 30.0 for RG-9. 5. I'm certain that it's not 75 ohm cable, because of the low SWR on every band through 10 meters. In one sense, I guess it doesn't matter, since I know enough about the cable to put it to good use. The only missing data that might be useful under some circumstances would be the Velocity Factor. Thanks for all your input. Lew K6LMP > > --- On Wed, 4/13/11, Lew Phelps K6LMP <k6...@me.com> wrote: > >> From: Lew Phelps K6LMP <k6...@me.com> >> Subject: [Elecraft] OT trying to identify "mystery" coax cable >> To: "Elecraft Reflector" <elecraft@mailman.qth.net> >> Date: Wednesday, April 13, 2011, 11:58 AM >> I was browsing through the local >> Salvation Army Thrift Store (where I sometimes go looking >> for low-priced antique treasures), and stumbled across a >> 50-foot length of RG-8-type coax cable. At the asking price >> of $6.00, I couldn't pass it up. >> >> It has Amphenol male "UHF" connectors. And absolutely NO >> markings on the cable itself indicating manufacturer or >> type. The OD of the cable varies from point to point, but >> averages about .405 inch, which puts it in the RG-8b family. >> It is quite flexible, and clearly stranded center conductor, >> not solid. Capacitance of the 50 foot cable >> was measured 1155 pF, or 23.1 pF per foot, which eliminates >> some RG-8 flavors that have 30 pF per foot. The only >> distinguishing feature of the cable is that there appears to >> be a wire would spiral-wise (1/2 turn per inch) outside the >> standard foil shield and under the exterior rubber >> sheath. I've never need that construction before on >> any RG-8 cable. (I haven't cut it open to verify the >> construction, because I don't want to have to de-solder and >> reconnect the Amphenol connector.) >> >> I attached the cable to my dummy load and to the HF output >> of my K3. Keying the transmitter at 12 watts produces >> an SWR of 1.05:1 (external SWR meter) on all bands up to 6 >> meters, and continuity checks confirm that the cable has >> neither short circuit between shield and cable nor open >> circuit. In other words, it appears fit for duty. >> >> Two questions; >> 1. Anything else I can or should do to check the cable and >> make sure it's OK to use? (Unfortunately, I do not own >> or have access to an antenna analyzer.) >> 2. Based on the "spiral winding" between the shield >> and outer coverk does anyone have an idea what specific >> cable this might be? >> >> Thanks, and 73 >> >> Lew K6LMP >> >> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:Elecraft@mailman.qth.net >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
