[TowerTalk] Wireman Balun kits

[Roger (K8RI)]

Jim Brown wrote:
> On Wed, 05 Mar 2008 23:58:11 -0500, Roger (K8RI) wrote:
>
>   
>> What I'm planning on winding is a 
>> 1:1 balun where both sides of the antenna are at aDC ground 
>>     
>
> I understand what you said, but there's some muddy thinking. If 
> you're thinking lightning protection, remember that MOST of the 
> energy in lightning is NOT DC, it is predominantly RF with a DC 
> component. The ENERGY in lightning (what fries things) has a VERY 
> broad peak centered around 1 MHz (and if you operate much 80M, your 
> ears tell you that there's still plenty up there). A DC connection 
> has little relevance to lightning. What matters is the RF path for 
> lightning induced current. 
>
> Again, I strongly urge that you study what I have published. 
>   

I have read all 70 some pages and I agree with it, but... have you ever 
watched a big fat blue arc extending as much as an inch out from the end 
of  a PL-259 just laying on the floor?  That's precipitation static, be 
it rain or snow and it is a differential DC voltage that  creates 
tremendous noise.  Even Ice or Polyphasers up at the antenna switch will 
not eliminate the noise although they will protect the rigs, but using a 
boradband transformer will turn that DC into a common mode voltage that 
will lessen the noise noticeably. OTOH when precip static is that bad 
there's usually so much noise you aren't going to spend much time on the 
band anyway. Another reason I want that to be a common mode is my 
antenna switches ground the unused cables and I don't want to have to 
install either ice or polyphasers "up there" 
Also by turning it into common mode I think I might get away by not 
grounding the center of the unused coax at the remote switch and the 
choke prior to the switch.  Also precip static on one antenna will 
bother all the antennas on the tower.

Nearby lightning strikes and direct hits are an entirely different 
matter.  Installing large  chokes (linear or toroid) at the antennas is 
not a satisfactory option  mechanically,  but is back by the remote 
switches which is where  I plan on using them.  The choke at the antenna 
serves one purpose, but doesn't do much to mitigate lightning when there 
are long runs of coax from the choke to the tower in which induced 
currents can be substantial.  The chokes back in front of the remote 
switches and grounding the coax shield to the tower can make a 
substantial reduction in the lightning effects/damage.  With all the 
direct hits the tower has taken (that I know about) have not damaged any 
remote switch. Nor have I had any antenna damage since going to this 
approach.  Prior to doing so I had one run of 7/8" Heliax blown out and 
multiple antennas damaged. 

I have a bit of work to finish but all coax from antennas to the tower 
has the shield grounded at the top (beams) or where the coax reaches the 
tower (slopers) and again at the bottom of the tower (all of them). A 
mix of ICE and Polyphasers are used where the cables enter the house 
through the bulkhead.

Another reason for the extra protection is I do not have the option of 
disconnecting any of the rigs or even computer networks unless I have 
plenty of warning. Doing so is a major undertaking as is reconnecting 
them.  Just the computers can take up to  an hour to get back up and 
running on the CAT5e network.

With weather watches it is common to operate up until the stuff gets 
really close and at that point there's no way I'm grabbing cables I 
can't see behind rigs.

One time I had the coax to the 144/440 rig disconnected at the rig. All 
of the coaxes come through a grounding bulkhead and single point ground 
with a very elaborate ground system.  That cable was only about 6 feet 
long and was connected to the grounding bulkhead.  Whether the strike 
hit the tower or was close I don't know, but there was about a 10" arc 
from the cable to the manual antenna switch on the desk.  It sounded 
like  a 12 gage shotgun being fired indoors.  That one also was tied 
back to  the bulkhead. So both of those 6' cables were grounded on one 
end and had a 10" arc between them at the other end. So now I figure 
it's all or nothing when it comes to disconnecting rigs.

73

Roger (K8RI)
> 73,
>
> Jim Brown K9YC
>
>
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
>