What is the significance of using RG11 75 ohm coax vs 50 ohm? Sorry if this is a dumb question.
Bob AF9W On Oct 26, 2012, at 10:39 AM, N5GE wrote: > All, > > There's a trick I learned from an antenna engineer acquaintance > recently for tuning 450 ohm feedline's with a 1:1 balun with 50 ohm > coax feeding the TX. > > Here it is: > > 1. Assemble three RG11 coax lengths. One coax 6 feet 7 inches long, > one coax 6 feet long and one coax 9 feet long. From these three coax > lengths you can test with four different lengths of 75 ohm coax; > 6' 7", 12' 7", 15' 7" and 21' 7". > > 2. Beginning with the 6' 7" cable and connect the coax between the > balun and the 50 ohm feed line, repeat the test below with each of > the lengths above. Connect the cables with double female connectors. > > 3. If you have an analyzer (MFJ analyzers work fine for this) that > gives the Rs, Xs and SWR go to step 4; If you don't go to step 6. If > you have an AIM 4170 analyzer, you are in luck. The AIM allows you > to do single shot analysis of a single frequency, displaying more > information than you need for this test. > > 4. Record the Rs, Xs and SWR of each combination at the frequency you > are interested in. A spread sheet makes this a little less tedious. > > 5. After recording the calculate the SWR the tuner will see with the > following rules: > > Disregard Xs. > > If the Rs is greater than 50 divide the Rs by 50. > if the Rs is less than 50 divide 50 by the Rs. > > The result will be the SWR the tuner is working against when > searching for a match. > > In my case I am looking for a calculated SWR lower than 10:1 to help > my KAT500 tuner find an acceptable match to my KPA500 and NVIS Loop, > which works on all amateur bands for close in Non-DX rag chew > communications. > > > 6. You can still do the test, but you will need to do it by testing > with the tuner for the best combination of matches at each frequency > of interest. > > If you are going to do the tests, remember to use the MINIMUM power > your tuner can tune with and allow time for your rig to cool down > between tests. > > 7. When you have completed your tests measure the length of the > joined test coaxes, including the double female connectors, and make > a piece of RG11 that length. > > DISCLAMER: I'm not a real technical guy and probably don't know as > much antenna theory as many of you, but what I have described worked > for me. Your experience may not be the same. > > Amateur Radio Operator N5GE > ARRL Lifetime Member > QCWA Lifetime Member > > > > On Fri, 26 Oct 2012 05:42:20 -0700, Ron Midwin > <[email protected]> wrote: > >> I recently bought an LDG AT600 Pro Automatic Tuner. >> >> I seem to be able to get a low VSWR on 80 & 40 meters, but on 20, 15, & 10 >> meters the best it will do is ~ 1.8:1. >> >> My "G5RV" (It's really a Van Gordon 80 meter all bander fed with 450 ladder >> line, 33 feet long, and then transitions to coax thru a 1:1 choke balun; >> coax is ~ 6 feet long. >> >> Has anyone found a configuration that works better on all the bands? >> >> Previously I have been using an MFJ 962D manual tuner that is able to tune >> down below 1.2:1 on all bands. >> >> AE6RH >> K3 S/N 1997 > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > 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:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
