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## Re: [TowerTalk] Coax

 To: "[TowerTalk]" Re: [TowerTalk] Coax "Joe Subich, W4TV" Mon, 09 Apr 2012 16:15:22 -0400 mailto:towertalk@contesting.com>
 ```> ## and its even easier with any digital wattmeter. It gets easier if > the max power is 100w on the 1st meter, and less than 100w on the 2nd > meter. This assumes that the two meters are identical, calibrated identically and with identical deviations with frequency. At the very least, I would take measurements "both ways" - once with meter 1 on the input and again with meter 2 on the input - and average the readings. That should reduce the calibration errors. > Once below 100w, then I’m down to reading power in .1 watt > increments. The Telepost (N8LP) LP-100 meters can provide readings to 0.01 watt below 150 (I think) watts. However, again, one needs to be concerned about calibration accuracy *and* significance. Just because one can read a meter to 10 or 100 mW, is 1 that even significant since the devices are rated for 3% accuracy (3 watts at 100 watts)? 73, ... Joe, W4TV On 4/9/2012 10:28 AM, Jim Thomson wrote: > > > From: TexasRF@aol.com > Sent: Monday, April 09, 2012 6:22 AM > To: jim.thom@telus.net ; towertalk@contesting.com > Subject: Re: [TowerTalk] Coax > > Jim, the example compares 200ft of LMR400 to RG213. The stated difference is > .358 dB/100ft for a total of .716 dB. > > That is a power ratio of 1.179 or 100w vs 117.9w. That is easily measured > with a bird meter. > > 73, > Gerald K5GW > > ## and its even easier with any digital wattmeter. It gets easier if the > max power is 100w on the 1st meter, > and less than 100w on the 2nd meter. Once below 100w, then I’m down to > reading power in .1 watt increments. > I own 4 of these power master watt meters. They are superb. The bird and > also my CD meter are long gone obsolete, > along with the myriad of slugs. > > Jim VE7RF > > > > In a message dated 4/9/2012 8:04:42 A.M. Central Daylight Time, > jim.thom@telus.net writes: > Date: Sun, 08 Apr 2012 21:11:58 -0700 > From: Jim Brown > Subject: Re: [TowerTalk] Coax > On 4/8/2012 9:01 PM, Jim Thomson wrote: > > LMR-400db .666 db > > LMR-400UF .799 db > > RG-213U 1.024 db > > RG213 is not a spec, it's a very broad generic description. There are > RG213s built with thin copper braid and others with heavy copper braid. > The loss in cable is a direct function of how much copper they use to > build it. Based on resistance data, Davis's 213 is directly equivalent > to LMR400 for use on the HF bands. > > ## say what. Run 200 feet of 213-U into a dummy load at the far end, with > a wattmeter 1 foot before the dummy load. > > > You'll need far more precise instrumentation than a Bird to measure a > difference of 0.1 dB Rather, you'll need a scope, RF voltmeter, or > spectrum analyzer that can resolve 0.01dB, you'll need to measure by > substitution, and you'd better make a bunch of measurements and compare > them. > > 73, Jim K9YC > > ## Andrew .5 inch heliax uses a copper clad solid aluminum center > conductor. Andrew is the not the only game in town. > Other makers will offer .5 inch heliax in both copper clad Al and also > solid CU. Are you trying to tell us that the solid Cu > variety will result in lower loss. .875 inch heliax uses a hollow copper > tube. LMR-600 uses 5.5 gauge copper (7 x strands) > for the center conductor. Which one do you think will have the lowest > dc resistance for the center conductor. > > ## If Davis RF’s version of 213 has way lower dc resistance than belden > 213, then the strands would have to be a LOT bigger. If that was true, > the OD of the cable would have to be a lot bigger, and all those 213 > cables appear to be .405 inch OD. You can’t just use heavier gauge strands > for the braid and be able to use the same pl-259. Well maybe you can, > if you made the sheath from thinner material to maintain the .405 inch > OD. t > > ## LMR cables use a tinned outer braid...on top of a 360 deg AL wrap of > foil. Most eng notes will tell you that 90% of losses in coax cable are > dielectric losses..and not dc resistance loss’s. > > ## Bird products have limitations to them. Any array solutions power > master wattmeters will read in .1 watt increments, but only below 100w. > Above 100w, they read in 1 watt increments. Pretty easy to see the > difference between 1500w and 1498 w. (.00579 db) or the diff > between 1500 and 1499 w (.002896 db) Pretty easy to measure the diff > between 1500w and 1467w (.00966 db) > > ## It would not be rocket science to measure the difference between > davis 213, Belden 213..and LMR-400. Use 200-300 feet of each > of the 3 x cables, as long as they are all identical length, and use the > same freq to test em.... like 29.0 mhz > > ## The problem with using any scope is... if the scope is off by say 5%, > your results will be off by twice that. Voltage squared divided by 50 ohms > = power. The bottom line is..even a bird will show the big diff between > 300 ft of belden 213 and 300 ft of .875 inch heliax on 29 mhz. Its like > apples and oranges. > > ## If you are implying that dc resistance is the predominant factor in > coax cable loss, then all these various formulae + online loss > calculators must be out to lunch, and I find that hard to believe. > > ## Bigger coax is cheaper than a bigger amplifier. I want a bare min of > 2.5 kw at the feed point of the ant on any band. With a crank up tower > I am limited to flexible coax up the side of the tower. The best I can > come up with is LMR-1200DB to the base of the tower..and RG-393 > up the side of the tower. > > Jim VE7RF > _______________________________________________ > > > > _______________________________________________ > TowerTalk mailing list > TowerTalk@contesting.com > http://lists.contesting.com/mailman/listinfo/towertalk > _______________________________________________ > > > > _______________________________________________ > TowerTalk mailing list > TowerTalk@contesting.com > http://lists.contesting.com/mailman/listinfo/towertalk _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
 Current Thread Re: [TowerTalk] Coax, (continued) Re: [TowerTalk] Coax, Gene Fuller Re: [TowerTalk] Coax, TexasRF [TowerTalk] Coax, Jim Thomson Re: [TowerTalk] Coax, Steve Maki Re: [TowerTalk] Coax, Jim Lux Re: [TowerTalk] Coax, Grant Saviers Re: [TowerTalk] Coax, TexasRF Re: [TowerTalk] Coax, Jim Thomson Re: [TowerTalk] Coax, Jim Lux Re: [TowerTalk] Coax, Jim Brown Re: [TowerTalk] Coax, Joe Subich, W4TV <= Re: [TowerTalk] Coax, john [TowerTalk] Coax, Jim Thomson