[TowerTalk] Freqent crank-up tower recmmendation

Sun Feb 28 19:30:38 PST 2010

Jim Thomson wrote:
> Date: Sun, 28 Feb 2010 02:57:39 -0500
> From: "Roger (K8RI)" <K8RI-on-TowerTalk at tm.net>
> Subject: Re: [TowerTalk] Frequent crankup coax recommendation
>
>
> Brahmangou at aol.com wrote:
>   
>> LMR400 is a solid center conductor cable, A poor choice for cranking up and 
>>  down.
>>  
>>   
>>     
> Depends... If you are talking about a mast with the coax spiraled around 
> it like a coiled spring it'll work just fine.
>
> ##  It still won't work... on a crank up. Nobody is about to spiral rigid coax around
> the tower itself... much less the mast on top.  Why not just use the correct coax
> to start with.. like LMR-400/600 Ultra Flex.... or the Davis Bury flex. The Davis
> Bury Flex sounds like the ticket.  Then the fellow  could bury the coax from shack
> to base of crank up.. and continue on up the side of the crank up.  
>
> ## No point in using rigid coax, like LMR-400DB  [solid center conductor]  going
> up the side of a crank up. IT WON'T FLEX.  
>
> ## I'm installing a HDX-689  in 2 x months.. and have the same issues.  My 
> proposed 'fix'   is to run LMR-1200DB, from shack to base of crank up,
> and either continue up the 1st 20'  of the bottom section of the new
> crank up, or up the 1st 20'  of the old tower... [ old tower is immedediately
> adjacent.. and it's all coming down, except the bottom 2-3 sections, Trylon].
>
> ##  LMR-1200DB, then is spliced into either  Tcom -600UF , or RG-393,
> both are flexible. One flexible cable up the side of the crank up, to
> AS remote switch box, mounted on mast.   Then 3-4 x separate runs
> of coax  to each ant.  By installing the remote switch box on the mast,
> there is only ONE  rotor loop involved,  not several rotor loops. 
>
> ## all coax braids get grnded at top of tower.   
>
>
>
> Would I use it that way? Probably not, but I would use it for a rotator 
> loop if the need arose and I know it works quite well if installed 
> properly. OTOH, As I ground the coax at the top and bottom of the tower 
> which means I am going to need a connector in the cable at that point 
> anyway, I might just as  well install a rotator loop using Davis 
> BuryFlex (TM) or another good, flexible cable. Three of the 4 loops are 
> 28' while the one to the tri-bander is only about 18'. With 4 cables 
> bundled together I need all the flexibility I can get.
>
> ##  are u using all these ant's  simultaneously??  
And more with the station set up for SO2R with VHF and UHF independent
of the other systems.
144 and 440 are often in use at the same time with the NWS and nets
where I can go direct while digital requires a couple of hops.
> IF not, why not use
> a remote switch box on the mast... and run ONE coax up the tower,instead
> of several of them??   For a fixed tower, I'd take ONE run of LMR-1200DB/
> 7/8"  heliax up the side of a tower any day... VS  2-6 x runs of  213-U....esp
> if you are talking about a long run of coax.  There is a huge diff  between
> LMR-1200/  7/8"  heliax VS  213.  213-U  has  FIVE  times the loss on 
> 10m alone! 
>   
I'm using LMR-600 on these.  The only run of 400 is to the 160 half
sloper. There are remote switches for the 75 and 40 meter half wave,
center fed slopers, but the top of that tower is a dangerous place for
switches.  It's taken 17 direct lightning strikes that I know of. How
many actual hits it's taken? I don't know.

Typical distance from rigs to antennas is 228' from the house and
roughly 180' from the shop.
There are two side mounted, 21' tall,  144/440 Diamond verticals as well
as the stacked pair of 11's on 440 and 12's on 144 @ 130'.  The
tribander is also run separate.  I've been QRO on all bands except 440
where we are limited to 50 watts out of the rig. That tempts me to
remote mount the RF deck at the feed point of a large array, but I think
I could probably get permission for EME as the array would have to
remain pointed 20 degrees, or more, above the horizon. OTOH it still
rules out point to point except for low power.

I'm also pretty well maxed out for antennas on the tower. Although the
25G is only 60 feet NW from the 45G, I could likely get away with a
tribander, multi-bander, or log at 60' which would open up the 45G for a
much larger array of 144 and 440 antennas and that would be a good
reason for LMR1200, but truth be told, I'd much rather have a 40 meter
monobander up there. Unfortunately any thing that massive is going to
require hiring some tower monkeys and equipment as I'm getting a bit too
long in the tooth for that kind of work.  I should have purchased that
shorty 40 that was offered to me about a year ago.

I'd not normally use the Ultra Flex versions for pigtails as the jackets
have not stood up well here.  LMR 600 "to me" is a reasonable compromise
It runs twice the attenuation of 1200 which is still only 0.4db/100' at
30 MHz, 1.0 db at 2-meters,  and 1.7 db at 450 MHz while LMR-400 is
0.7db at 30 Mhz or about twice that of LMR600. It's 2.7db at 450 which
I'd call close enough to lose half the power while 600 is a bit over
half that at 1.7db.  Connectors are also much more reasonable for LMR600
than 1200. IIRC LMR100 is also about 3X the price of 600 and 600 is less
than twice the price of 400 at roughly $1.50 something although the last
batch I purchased was only $1.29 which is about what I paid for 9913
when it first came out.

73

Roger (K8RI)
> Later... Jim   VE7RF
>
>
>
> 73
>
> Roger (K8RI)
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