[RFI] Ladder Line and RFI/Noise

[dalej]

I use the antenna on MARS frequencies and other bands including 40 m., I like switching between the inv. Vee and doublet, I might add a vertical in the future.  

Anyway, my noise boxes pretty much take care of the problem and I do like the flexibility of the multiband doublet, I might however go back to the window 450 ohm open wire if that affords less noise pickup.  Would that be a good choice?

Thanks, this is very good information.  

73
Dale, k9vuj



On 19, Oct 2010, at 16:10, Jim Brown wrote:

>  On 10/19/2010 1:27 PM, dalej wrote:
>> I am not convinced that in my case, coax would work better than open wire feeders regarding the noise problem.
> 
> As I understand the problem, the answer is, it depends. :)  In this 
> case, it depends on the location of noise sources with respect to 
> feedlines and the antennas themselves, the electrical length of the 
> feedlines, and whether the coupling is common mode or differential mode. 
> It also depends on the antennas connected to the noise sources, and 
> their directivity and orientation. That's a lot of variables. No magic, 
> but not easy to compute, and one size clearly does not fit all.
> 
> One of the principles at work here is that each design problem involves 
> trade-offs, and is best approached by thinking through all of the 
> variables.  What would be the loss of coax in a given situation, how 
> important is it that one antenna work all bands, what are the noise and 
> RFI issues in THIS installation, how easy is it to do it in the more 
> ideal way, etc.
> 
> As to the validity of N7WS's work on the effect of moisture on ladder 
> lines, and on other twin leads, I would expect that to depend a lot on 
> the construction of the line (how much material other than air in the 
> dielectric space and what that material is), and upon any degradation of 
> that material due to UV and weather that might cause it to be more 
> porous. Wes's is the only work I've seen on this topic, nor have I seen 
> any serious peer review of it other than the comments that N3LI just 
> posted.
> 
> 73, Jim K9YC
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