[RFI] 160m spur

[mstangelo at comcast.net]

Gary,

Thanks for the reminder on the importance of regular maintenance and the explanation about of the lightning loop.

I saw a picture of this loop on Jim Hawkin's excellent site from WCBS/WFAN and wondered what the loop was used for.

Looking back I see Jim included the explanation with the picture:

<http://j-hawkins.com/wcbs_wfan/cbsfan_twr14.jpg>

Jim also has pictures and describes diplexer operation. 

Mike N2MS


> On 01/11/2023 1:15 PM Gary Peterson <kzerocx at rap.midco.net> wrote:
> 
>  
> I am reminded of two situations.  When I was corporate engineer for a company that owned almost 50 stations, I received a call from one of our market engineers.  He had two diplexed AM stations and an excessive third-order mix was being radiated.  I told him to pick a time when he could shut both stations down and tighten everything up in the diplexer and antenna matching system.  He did and the problem was gone.  Temperature cycling and vibration from wind can loosen up hardware between inductors, capacitors, RF contactors, etc.
> 
> A contract engineering friend was trying to determine why an AM station had excessive harmonics being radiated.  He was poking and tapping components at the tower and antenna tuning unit, while monitoring the level of one of the harmonics on a Potomac field intensity meter.  The poking and tapping was done with an old, dry broom handle.  When he was rapping on the “lightning loop” between the ATU and the tower, the weld broke loose and started arcing.  A lightning loop is a large, one turn loop  in the copper tubing between the ATU and the tower.  It represents a blob of inductance which, supposedly, encourages more of the lightning to choose the spark gap across the base insulator, rather than the ATU on its path to ground.  Apparently, over time, the lightning loop’s brazed connection to the tower work hardened, due to jiggling slightly in the wind.  The weld separated, microscopically, under the red tower paint.  The only thing that was holding the copper tubing to the tower was several layers of hardened tower paint.  Once the lightning loop was cleaned and re-brazed, the  harmonics were down to normal levels.
> 
> Both of these are good examples of entropy.  Unless work is done on a system, it will proceed toward a state of maximum randomness.  Perform regular maintenance on it or it will eventually fall apart.
> 
> Gary
> K-zero-CX
> 
>       
> 
> And you should not discount the probability that the 'mix' is caused by 
> a corroded joint between two conductors somewhere.? The rusty joint 
> could be any where, in the near field of the TX or near the RX. Anywhere 
> there is enough RF to excite the joint and re-radiate.
> 
> AL, K0VM
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