[600MRG] Coax shielding effectiveness

[lstoskopf at cox.net]

Thanks for this thread. 60 years of hamming and I never would have dreamed that for a 'perfect' station I needed solid Heliax on 630M! Luckily signals sneaking in or out of my coax in central Kansas seems not to be a problem! N0UU


> On December 9, 2019 at 1:28 PM Gedas <w8bya at mchsi.com> wrote:
> 
> 
>     See if this will get you started.
> 
>     http://www.repeater-builder.com/antenna/andrew/andrew-shielding-effectiveness.pdf
> 
>     Gedas, W8BYA
> 
>     Gallery at http://w8bya.com
>     Light travels faster than sound....
>     This is why some people appear bright until you hear them speak.
> 
>     On 12/9/2019 2:23 PM, david vanhorn wrote:
> 
>         > >         I knew fsj1-50 would be good but I haven't found data from anyone at these low frequencies. Any pointers would help.
> > 
> >         On Mon, Dec 9, 2019, 12:14 PM Gedas < w8bya at mchsi.com mailto:w8bya at mchsi.com > wrote:
> > 
> >             > > > 
> > >             Hi Dave. Funny you should ask. I am right in the middle of making a video where I test about 10 different (and common) coaxial cables specifically for their SE. The project is on and off as I just have too many pokers in the fire right now.
> > > 
> > >             It is not as simple as one may think to measure the SE accurately esp if the cable is of high quality and has a high SE. If I were still employed and had access to my old lab and shielded enclosures and able to generate & measure known RF fields from DC to daylight it would be a much, much easier task. Having to do it in my basement lab makes it a much more challenging project. In the end I chose to arrive at the SE by measuring the cross-talk between two identical coax cables.
> > > 
> > >             My methodology is to lay two identical cables of equal length next to each other on a plywood table. Both far ends of the coax cables are terminated in 50 ohm loads. One cable is driven with a tracking generator (then broadband power amplifier) while the other coax fed into the input of my spectrum analyzer. The amount of cross-talk between the two cables can then be used to directly see what the SE was. It gets hairy if the cables have a high SE as the SA has a limited sensitivity (NF) and I can only generate several watts of broadband RF from DC to about 1 GHz.
> > > 
> > >             Until that video is done you will have to go by OEM data. FSJ1-50 will have an extremely high SE (well over 100 dB). If you need some help looking up the exact OEM data just hollar. 73
> > > 
> > >             Gedas, W8BYA
> > > 
> > >             Gallery at http://w8bya.com
> > >             Light travels faster than sound....
> > >             This is why some people appear bright until you hear them speak.
> > > 
> > >             On 12/9/2019 1:37 PM, david vanhorn wrote:
> > > 
> > >                 > > > >                 I've been searching around without much success.
> > > >                 I'm trying to find data sheets or good measurements of shielding effectiveness of the various coax types, including FSJ1-50 for this band.  I'm not seeing anything talking much below 100MHz.
> > > > 
> > > >                 Can someone point me in the right direction?
> > > > 
> > > >                 --
> > > >                 K1FZY (WA4TPW) SK  9/29/37-4/13/15
> > > > 
> > > > 
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