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Re: [TowerTalk] Coax

To: Jim Thomson <>
Subject: Re: [TowerTalk] Coax
From: Grant Saviers <>
Date: Mon, 09 Apr 2012 09:28:30 -0700
List-post: <">>
Having recently installed 1000 feet of 9913-F7 and 1500 feet of 
Bury-Flex I thought I pass along some observations:

The 9913-F7 braid "prints" on the outside of the cover, which I think 
makes it more difficult to seal against moisture.  The cover is also 
noticeably less tough than the Bury-Flex.  The 9913 is slightly more 
flexible, but not enough to matter in making chokes or rotator loops.  
In fact, the stiffer Bury-Flex is a little easier to dress in a rotator 
loop that stays in place.

The 9913 I installed a few months ago showed some oxidation of the braid 
tinning, when I installed a new connector, so that is a concern.  Some 
Bury-Flex looked great after the same exposure.

Both are about the same cost from DavisRF and have virtually the same 
specs (1.5db loss/100' @ 100MHz), however Bury-Flex is the winner for me.


On 4/9/2012 6:04 AM, Jim Thomson wrote:
> 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
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