[Top] [All Lists]

[TowerTalk] Baluns...again

To: <>
Subject: [TowerTalk] Baluns...again
From: "Jim Thomson" <>
Date: Fri, 27 Aug 2010 02:21:15 -0700
List-post: <">>
I just recently received a pair of AS line isolator's.  I had Jay + Bob  modify 
of the W1JR baluns.. and  put  7-16 Dins  on both sides of the large 
NON-conductive nema box.
Inside, it consist of  4 x 'pass throughs'  of  RG-393 coax.   IE:  3 x 
external loops  of 
RG-393.    The coax is arranged in a neat row, solenoid fashion, and not 
scramble wound.
Unlike the K9YC versions, with the external loops  spread far apart, the loops 
on mine are
packed in tight,    4 x  2 .4" OD , type 31 cores are used.   The axis of the 
cores is horizontal.

Everything is ty-rapped 16  ways to Sunday.  Nothing moves, even with box 
inverted and shaken.
The 4 x cores + coax are dead center in the middle of the nema box... with 
loads of space below the
4 x cores.  If mounted on a boom, etc, there is no stray C added. 
I put my B+K  875-B  LCR meter  between the hot sides of  both connectors and 
measured 128 uh. 
And  128.4 uh  between the 2 x outer shields  of the same connectors.  Anybody 
hazard a guess
what the choking Z of this  arrangement would be..between 160-10m? 

One of these line isolator box's  will be installed on the INPUT side of my  1 
in, 6 out remote switch box. 
The remote box grnds the braids of all 7 x coax cables  to the mast it's 
mounted to.  Since the line isolator 
is on the INPUT side of the remote switch box, the shield on the output side  
line isolator is also grnded..through
a very short piece of coax.  Will the line isolator even work in this config ?  
[ with the ant side of it grnded]  

The 2nd line isolator is to be mounted on my SPG,in the basement, which conists 
 of a large sheet of 
1/4"  thick AL plate.  The plate has a 1-0 cable  running to outside 8' grnd 
rod  [cadwelded] .  Bare  2 ga CU
wire  is run just below  the dirt.. all the way back to the tower.. and C 
clamped, and tied into the 3 x  8' rods 
at the base of the tower  [ 3 x more cadwelds, below  grnd level].   2 ga [ 
RW-90] is used to cable from each
of the 3 x grnd rods to  the 3 x tower legs. 

I was planning on putting the lightning arrestor on the SPG plate,  followed by 
the line isolator, then the  LP filter.
After drawing this out, I think the 2nd line isolator would be rendered 
ineffective...since both sides of it are 
bonded to the AL plate via short coax on each side.  The lightning arrestor of 
course is bonded to the al plate..
as is the large LP filter.   If the idea is to have a High Z on the outer braid 
of the coax, then  grnding both sides
of the line isolator [ through short coax] I would think would render it 90% 
ineffective ?   Any residual  RF current
on the outer braid would simply   'flow around' the  line isolator... via the 
SPG AL plate. 

Plan B was to swap the line isolator  and LP filter.  Done this way.. only one 
side of the line isolator is bonded to
AL plate [ant side] ... via the real short coax between line isolator + LP 
filter.    Will this work ?      Trbl is...if I
run a  10' long,  6 ga wire / safety grnd, from RF amp chassis   to  SPG...  
I'm back to having grnded both sides of the line 
isolator again.  

Plan C  is to install the 2nd line isolator  BEFORE the lightning arrestor.  
Done that way, the  XCVR/amp  side of the 
line isolator is grnded to the SPG plate... [ and not the ant side] .    I 
don't like the  idea of the lightning arrestor 
being downstream from the isolator, it may then render the lightning arrestor 
ineffective, due to the high Z of the
isolator ?      BTW,  I have a 2nd lightning arrestor at the base of the tower, 
 tied into the  grnd system at base
of tower. 

The pair of line isolator's  was to just supplement the existing, individual 
bead baluns used at the DE of the
4 x ants on the mast.   [ 3 x yagi's  =  1 x rotary dipole] . 

Tnx...... Jim   VE7RF              

TowerTalk mailing list

<Prev in Thread] Current Thread [Next in Thread>
  • [TowerTalk] Baluns...again, Jim Thomson <=