[TowerTalk] LMR600 up to the top of tower ? Respon fr DAVIS RF
Roger (K8RI) on TT
K8RI-on-TowerTalk at tm.net
Sun Aug 2 18:55:51 EDT 2015
All good info and in theory the Polyphaser at the top is sound. OTOH is
it practical and how much additional protection does it give over one at
the base of the tower? That would be the first thing to fail from a
nearby, or direct strike. If the top of the tower is easily reached,
then by all means go for it, but if it requires a long climb in
inclement weather I'd think twice. We get lots of thunderstorms in
spring and fall when climbing can be miserable. When my tower was
taking 3 visually verified hits per year, they quickly proved
impractical and expensive. The capacitance and inductance of the coax
usually reduces the differential voltage to the point where the
protective device at the base of the tower survives. If the strike is
powerful enough to damage the coax, it's also going to take out
connectors and probably do a lot of damage "up there". I've had strikes
that removed all the weatherproofing as well as the silver plating on
the connectors, leaving them looking like sandblasted brass, yet the
coax was not damaged nor were the internal parts of the coax connectors.
I did have to replace two Polyphasers. One at the tower base and one at
the CPG plate at the house entrance for the coax to the 2-meter array.
Other than the weatherproofing and the plating on the connectors there
was no additional damage. The rigs were hooked up and on at the time of
that strike.
About the Northern half of the US suffers from frozen ground. Some areas
with many freeze, thaw cycles. These cycles cause stones (large and
small) to slowly move toward the surface with lots of power that can
easily puncture most coax jackets. BuryFlex (TM) has a great advantage
here. So damage from above is not the only worry. However, direct bury
where the ground freezes for a third of the year limits your options in
case of failure making conduit a better choice. Again, BuryFlex (TM) is
much easier to pull than most other cables. If the run is long and
conduit is not an option (Sewer pipe is cheap and works as good as
conduit if buried deep enough). Although not as durable as schedule 40
PVC, it sure beats direct bury up here.
BTW the past few years the frost has only penetrated to about a quarter
of what it did when we moved here in 84. We used to be able to get some
pretty heavy equipment into the yard once the ground froze, but not recently
The other point, although the grounding kits are the most efficient, up
through 2-meters, I use grounded bulkhead connectors at the top and
bottom of the tower. Yes, I know those losses add up, but for HF and
low VHF are they worth any concern? With the patch panel, 6-pack for
SO2R and remote antenna switches I may have as many as 10 connectors in
a 220 foot coax run with the loss still being miniscule as calculated
and as measured via the AIM.
Between complete stations (1.8 through 440) in the shop and house, plus
the SO2R operation, I have close to 100 total coax connectors. Although
I'd prefer DIN, I have type N for the 144 and 440 bands and UHF for the
lower bands.. That's a lot of connectors to change, but I am looking
for some at a good price.
BuryFlex(TM) as a rotator loop. I have used a 2 turn coil about 16 to
18 inches in diameter laying on the flat tower top plate. It certainly
could be less than that. It's tough, slippery, and flexible which makes
it ideal for rotator loops.
73
Roger (K8RI)
On 8/2/2015 12:43 PM, Stephen Davis 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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>> 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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73
Roger (K8RI)
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