[600MRG] Coax shielding effectiveness

Mon Dec 9 16:19:36 EST 2019

no problem. SE is reciprocal meaning it is a property that not only 
helps ensure RF does not radiate outwards past the shields but it will 
also help keep unwanted RF (noise and RFI etc) from getting into your 
coax. Also, down at these frequencies a good quality double-shielded 
coax like RG-214, RG-213, etc will work just fine. That type of coax and 
a couple properly made common-mode chokes are all you need. One final 
note is that even the absolute best coax in terms of SE can be rendered 
near useless (in terms of SE) if not properly terminated ! The shields 
must be properly bonded to the connector case and that to equipment 
chassis. 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 4:07 PM, lstoskopf at cox.net wrote:
> 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 athttp://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 athttp://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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