[RFI] Ladder Line and RFI/Noise

[dalej]

If I grounded out the doublet then would that eliminate the re-radiation to the inv Vee, if that were the case?

I suppose for the sake of argument, I could re-install my coax fed 80 m. dipole and check again. I use 100 feet of OL line.  The neighbor with noise dimmers is about 200 feet away.   

I got to hurry though, winter is just around the corner.  

73
Dale, k9vuj


  
On 19, Oct 2010, at 16:13, W2RU - Bud Hippisley wrote:

> How do you know your wide-spaced OWL isn't picking up noise that is then radiated by your 135-ft doublet and re-picked up by your 40-m inverted V to be sent down your 52-ohm coax to your receiver?  In that case, your choke balun on the 40-m coax cable has nothing to do with anything.
> 
> Bud, W2RU
> 
> On Oct 19, 2010, at 4:27 PM, dalej wrote:
> 
>> I have 135 ft doublet fed with 100 ft of wide spaced open wire line to a Johnson KW match box.  I also have a 40 m. inverted V fed with 70 ft of 52 ohm coax and choke balun, both are suspended at the same point on my tower and oriented in the same direction.  I hear my neighbors light dimmer equally well with both antennas tuned to 40 meters.  I am not convinced that in my case, coax would work better than open wire feeders regarding the noise problem.
>> 
>> 73
>> Dale, K9VUJ
>> 
>> 
>> On 19, Oct 2010, at 12:31, Jim Brown wrote:
>> 
>>> On 10/19/2010 8:35 AM, Howard Lester wrote:
>>>> Gene right
>>>> off asked me if I was feeding my antenna with ladder line. I replied "Yes,
>>>> and it runs through the wall and connects directly to the transmatch on my
>>>> desk." He said that was the problem.
>>> 
>>> Yes. Folks have bought into the notion that ladder line is a cure for 
>>> all ills, that you can put up any wire and feed it with no problems. 
>>> Nothing could be further from the truth. The monster hole in this 
>>> approach is NOISE and RFI. The developers of telephone communications 
>>> learned more than a century ago that twisted pair was at rejecting noise 
>>> and crosstalk, and that parallel wires were bad.
>>> 
>>> Why this is true is pretty simple. Voltage is induced in both wires, and 
>>> if it is equal, the receiver will see zero voltage. But if the voltages 
>>> are slightly different, the receiver will see the difference. If the 
>>> noise source is relatively close, it will be closer to one conductor 
>>> than the other, so the voltage will be slightly different. With twisted 
>>> pair, one conductor will be closer at one point on the line and the 
>>> other will be closer a fractional inch down the line, so the induced 
>>> noise is much closer to zero, and the cancellation is more nearly perfect.
>>> 
>>> This discussion applies to differential coupling. There's also common 
>>> mode coupling, of course, and antennas fed with ladder line rarely have 
>>> a common mode choke. But they NEED a common mode choke, because nearly 
>>> all ham antennas have at least SOME unbalance by virtue of asymmetry in 
>>> their surroundings, their length, etc.  Yes, coax has more loss and it 
>>> costs more, but we can choke it, and there's no differential coupling at 
>>> proper connections.  And all of this works in reverse, of course, by 
>>> reciprocity, so ladder line puts more RF in your neighbor's A/V system 
>>> and computer speakers too.
>>> 
>>> 100 years later, we use parallel wires for speakers and power wiring. El 
>>> dumbo grande. Replacing them with twisted pair solves a LOT of noise and 
>>> RFI problems. And ladder line is a TERRIBLE idea if you have neighbors. 
>>> Or any noise generators in your home.
>>> 
>>> 73, Jim Brown K9YC
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>> 
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