[TowerTalk] LMR600 up to the top of tower ? Respon fr DAVIS RF

Robert Harmon k6uj at pacbell.net
Sun Aug 2 14:21:29 EDT 2015


Steve,

 After calculating loss when studying the different feed lines, then thinking about the connectors, 
 it is painful to then think about introducing loss back in with connectors.  I see the insertion loss 
 is extremely small with the connectors, so no worries.  
I am definitely going with BuryFlex for the rotator loop and up to the ant connections.  The run is fairly
short and I found the loss is not that much different compared to LMR400 especially for a short run like this. 

Now to decide feed line to the tower.  I have some good options to consider thanks to you and and 
the other posts.  I wont be burying the feed to the tower and Cellflex looks attractive.  Nice low loss, comparable to 
Heliax,  and more flexible than Heliax I understand.   

Thanks for the info Steve, much appreciated.

73,
Bob
K6UJ



 



> On Aug 2, 2015, at 9:43 AM, Stephen Davis <sdavis at davisrf.com> wrote:
> 
> John and Charlie are correct, no need, and physically impractical, to be running one type of coax all the way to top and or to antenna.  Noted was Bury-Flex ™ . At HF & VHF , the attenuation difference is minimal, LMR400 vs. Bury-Flex ™  (I'm partial to Bury-Flex ™ ….maybe say I'm biased because I designed it).  Although I don't know the length you have to run, thus the actual attenuation difference. I can provide that to you for any choice of cable you want to analyze, just need freqcy range of the application and length.   Bury-Flex ™ can be used as a rotor loop, just add about 20% more length than you would for an RG-213 or similar loop.   LMR 400 UF for a loop:  NO,  the outer jacket is TPR, won't last as long as Bury-Flex ™  or  9913F7.     We can equip you with any coax you want.  1/2" Heliax you can direct bury (same for LMR-600,  the 600 also comes in a DB (direct bury)  but you will be OK using their std. 600, it has exactly the same outer jacket PE, the DB just has the "Grease" which is only there to fill any knick in the outer jacket if you just happen to drive a stake, or roto till (yikes, in the area of your cherished buried cable  HI) in errant fashion.
> The grease will also act as a thermal barrier against wide swing temperature inversion… but that usually is only an issue where moisture is already inside and the temp drops a lot.  Or you take the reel of cable from your 70 deg F  , into cold outdoor temps.
> 
>  Grounding the shields:  we have some not so expensive grounding kits which you just cut away the out coax insuation, clamp it on and the other end of the grounding wire that comes with it
> can be clamped to tower leg.  Yes, it is real good idea to ground at top and bottom, but that theory usually is associated with using an inline surge protector, Polyp[haswer, at top and bottom. Without the surge protector, the only thing you are really giving a ground path for is the outer shield conductor vs. the center conductor would also be protected with a Polyphaser device.
> 
> Lastly, don't worry about putting connectors into the coax feed line, i.e.  bottom and top of tower, at the entrance panel to your house or shack, and 
> a transition at the drip loop.  So many hams worry about insertion loss of connectors and adaptors.  THe max insertion loss of a good commercial grade connector or adaptor is only .200 dB
> at the MUF of the connector.  UHF females and males (SO 239 and PL 259 )  are MUF 300 MHz.  The X to Y is linear so  if you are operating at 30 MHz, you insertion loss would be 
> 30/300 =  .10  X  .200 at MUF =  .02 dB per connector or adaptor. 
> 
> 73 Steve, K1PEK   DAVIS RF Co.            
> 
> 
> On Aug 2, 2015, at 9:42 AM, towertalk-request at contesting.com wrote:
> 
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>> Today's Topics:
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>>  1. Re: LMR600 up to the top of tower ? (Charlie Gallo)
>>  2. Re: LMR600 up to the top of tower ? (Steve Sacco NN4X)
>> 
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>> 
>> ----------------------------------------------------------------------
>> 
>> Message: 1
>> Date: Sat, 1 Aug 2015 22:02:45 -0400
>> From: Charlie Gallo <Charlie at TheGallos.com>
>> To: john at kk9a.com
>> Cc: towertalk at contesting.com
>> Subject: Re: [TowerTalk] LMR600 up to the top of tower ?
>> Message-ID: <1210224415.20150801220245 at TheGallos.com>
>> Content-Type: text/plain; charset=iso-8859-1
>> 
>> 
>> On 8/1/2015 john at kk9a.com wrote:
>> 
>>> I would never run one piece of coax underground that far and then up the
>>> tower, especially with a crank-up.  The tower piece will likely get damaged
>>> at some point.  LMR600 is not that flexible and certainly would not be good
>>> for your rotator loop.  I would direct bury large Heliax underground and
>>> then use something flexible and tough (like Belden 8267) on the crank-up
>>> tower.
>> 
>>> John KK9A
>> 
>> Yep  -  Remember,  your coax shield should be tied to the tower at the
>> bottom AND the top.  (Gee,  yes  you can carefully strip the outer jacket and bond,
>> but  easiest way is something like a PL-259 bulkhead connector mounted
>> to the tower (or polyphasor or similar - at least at the bottom)
>> 
>> You  can  easily  transition from one type of coax to another at these
>> points - tun the 600 to the bottom of the tower, and then buryflex (or
>> say  LMR400)  up, and then transition to something flexible at the top
>> ground  point.  All done, simple, and you are on your way to the start
>> of proper grounding too
>> -- 
>> 73 de KG2V - Charles Gallo
>> Quality Custom Machine-shop work for the radio amateur (sm)
>> 
>> www.baysidephoto.com
>> www.thegallos.com
>> 
>> 
>> 
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