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@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)
>
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Sat, 1 Aug 2015 22:02:45 -0400
> From: Charlie Gallo <Charlie@TheGallos.com>
> To: john@kk9a.com
> Cc: towertalk@contesting.com
> Subject: Re: [TowerTalk] LMR600 up to the top of tower ?
> Message-ID: <1210224415.20150801220245@TheGallos.com>
> Content-Type: text/plain; charset=iso-8859-1
>
>
> On 8/1/2015 john@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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