[TowerTalk] Coax Question

[Roger (K8RI)]

Jim Thomson wrote:
> Date: Tue, 13 Apr 2010 21:53:49 -0700
> From: jimlux <jimlux at earthlink.net>
> Subject: Re: [TowerTalk] Coax Question
>
> Kipton Moravec wrote:
>   
>> On Tue, 2010-04-13 at 07:15 +0000, van wd8aam wrote:
>>     
>>> In regards to long runs of coax, has any thought EVER been
>>> given to RG213 to a remote tuned high power amplifier
>>> at the base of the tower.  I've thought about it, and for
>>> costs, it might be cost effective.  I'm sure someone has this
>>> working for them somewhere.  What do you guru's say to this?
>>> van
>>> wd8aam
>>>       
>
> ##  it's already been done.. and that was 10 yrs ago ! 
> The kicker is... if you have say 3 db of loss back to the
> station, then you need an extra 3db of drive power. You 
> also LOSE  3 db on RX !    You also require a LONG run of  240 vac
> line, to base of tower,   OR a 240-600 vac  xfmr  at the house..
>  then  another  600-240vac step down xfmr at base of tower. 
>
> ##  getting the power out there is gonna  kill it right there. 
> 600-240  xfmrs  [can be run either way]   in 5-10 kva 
> variety are available surplus.. then  some small ga wire
> could be used.  Usually, the xfmr at the far end will have
> taps on it.. like 575v.. or 550v etc.... to factor in the V drop,
> so u end up getting the full 240 vac... but only under full bore load.
> No load, the V will rise > 240vac .  BIG  ga  AL wire between the
> 2 x xfmr's would work. 
>
> ##  Ok, now you need a small, secure, heated building, to put the
> xfmr plus 1.5 kw amp, plus any SDR radio, etc. 
>
> ## In the final analysis, cheaper to just use BIG coax.  
>
> ##  Most telco's in NA, have what's called an "IRG"
> [inventory recovery group]... usually now run by contractor's, whose
> job it is to store un-used eq.. AND cable.   They sell cheap, to dispose of this
> junk, at pennies on the dollar.  A buddy in W7 land  picked up several 
> 1000' spools of 7/8"  heliax, NEW... for  $116.00 per reel.  The usual deal is,
> some proposed cell site  new job/addition gets cancelled, AFTER the eq has 
> arrived.  It then all goes to the IRG warehouse.  Meanwhile, the same engineer
> orders all new eq  for yet another site !   Most of the contractor's  at the various IRG's
> wouldn't know  heliax  from a hole in the grnd.  Lot's of other good stuff, like
> 19" /24"  racks, etc.   You have to be in the right place.. at the right time.. you
> snooze, you lose.  If you see  5 x 5'-6' diam reels of coax... and it sez 'ANDREW' 
> on the side of it, snap it up, pay CASH, and get it outa there asap. 
>
> Andrew also makes heliax in corogated AL shield   these days... [ instead of
> Cu]   The newer AL stuff still uses a CU  tube in the middle. 
>
>
> ##  Plan B is the catv coax route.  Most of their stuff is  3/4" OD, with a 8 ga center
> conductor. Solid AL sheath, so you need the coring tool, to put the fittings on em.
> Modified LMR-600  connector's  might also work. 
>   
This is just one of the ways for adapting 3/4" to UHF 
http://www.rogerhalstead.com/ham_files/conn.htm

73

Roger (K8RI)
> later... Jim   VE7RF  
>
>
>
>
>
>
>   
>>> At 06:04 4/13/2010, you wrote:
>>>       
>>>> On Mon, 12 Apr 2010 21:07:25 -0400, Steve Bagley wrote:
>>>>
>>>>         
>>>>> I am putting up a tower and will need to run about 500 feet of coax.
>>>>>           
>>>> http://audiosystemsgroup.com/Coax-Stubs.pdf
>>>>
>>>>
>>>>         
>> I would probably put a Software Defined Radio (and computer) at the base
>> of the tower and run Ethernet cable back to the shack. Even with that
>> you will need a switch in the middle as Ethernet has length limit of 300
>> feet.
>>
>> Kip
>>     
>
> Use an 802.11 wireless LAN link with directional antennas.  Now all you 
> do is run AC power out there.
>
>
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