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Re: [TowerTalk] Coax

Subject: Re: [TowerTalk] Coax
Date: Mon, 9 Apr 2012 09:22:14 -0400 (EDT)
List-post: <">>
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.
Gerald K5GW
In a message dated 4/9/2012 8:04:42 A.M. Central Daylight Time, 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 

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  
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 
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 
=  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 
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      

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