[600MRG] Coax shielding effectiveness

Gedas w8bya at mchsi.com
Wed Dec 11 10:16:18 EST 2019 

For frequencies like 630m etc RG-214 is an excellent choice (it would be 
my #1 choice). It is WAY more flexible and if it is MIL-Spec (M17) cable 
then it uses silver coated copper conductors for the dual braids and the 
center conductor.

What kind of length(s) and number of cable(s) are you looking for? Brand 
new RG-214 that is MIL-Spec can get pricey. I happen to have plenty for 
myself and probably enough to share with others. Let me know what your 
needs are.

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 12/11/2019 9:11 AM, david vanhorn wrote:
> I did get some FSJ1-50 jumpers from Andrew, F1B-PNMBM-1M, and they are 
> way better than the Pasternak "100% shield" cables, but they still 
> leak at the ends.
> In the middle, essentially no leak.  So I suspect the ends aren't 
> being done completely correctly.  I haven't carved into one yet to 
> find out.
>
> That makes me think about making my own cables, which makes me think 
> in the direction of "Superscreen" or "Double Superscreen" cables.
> Unfortunately I have not been able to look up any source for those 
> cables, much less the connectors.
>
> Heavy sigh..  Designing sensitive receivers isn't that big a problem, 
> but it seems all the ancillary bits are determined to drive me nuts.
>
>
> On Mon, Dec 9, 2019 at 5:34 PM Gedas <w8bya at mchsi.com 
> <mailto:w8bya at mchsi.com>> wrote:
>
>     Labas Ed !
>
>     Wow those are some awesome relays to have that kind of isolation,
>     esp at 1296. I am WAY behind on my antenna work here as well. Just
>     today I had to lower the tower AGAIN after I found yet more
>     lightning damage from last year. Once done I may be able to put up
>     the next experimental 630m antenna I am pondering. I am needing a
>     VLF QSO fix.
>
>     Speaking of which, Ed made a special stop near my QTH last year so
>     we could have a very memorable eye-ball QSO. I will have to find
>     that picture and post it to the group. Merry X-Mas if we do not
>     chat before that time Ed. 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 6:35 PM, Edward R Cole wrote:
>>     Pretty much how I measure RF isolation.  In commercial
>>     communications: typically important to avoid desense in duplex
>>     operations.  Use of dual-shielded coax to obtain 90-dB.
>>
>>     In ham radio its mostly port isolation in TR relays.  I did
>>     essentially the same process as Gedas.  My eme preamps are the
>>     most sensitive so look at the leakage level with 10-100w in the
>>     Tx port.  I could not see any signal at 100-dB on 1296 with my
>>     Narda relays (cited at 80-dB). Since my max transmission power is
>>     600w (+58 dBm) that keeps leakage into my preamps way below 0 dBm.
>>
>>     I run Heliax transmission line and see no leakage signal into the
>>     Preamp on 144-MHz.  Space loss from antenna to receiver is less
>>     so it sees the transmitted signal if radiated.  So definitely
>>     need terminations in these tests.
>>
>>     Thanks for the info, Gedas.
>>
>>     My 630m inverted-L will not be in-service until next spring as I
>>     did not get my radial system planted this year (new lawn).  Also
>>     base loading coil is to be installed inside new fiberglass
>>     wx-proof cabinet which will also house my 2m-1500w PA & 50v PS.
>>
>>     Winter arrived!
>>
>>     73, Ed - KL7UW
>>
>>     At 10:14 AM 12/9/2019, you wrote:
>>>     Content-Type: multipart/alternative;
>>>      boundary="------------78ED9BB5007D8DB12F1545D4"
>>>     Content-Language: en-US
>>>
>>>     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
>>>>
>>>>
>>>>     ______________________________________________________________
>>>>     600MRG mailing list
>>>>     Home:
>>>>     http://mailman.qth.net/mailman/listinfo/600mrg
>>>>     Help:
>>>>     http://mailman.qth.net/mmfaq.htm
>>>>     Post:
>>>>     mailto:600MRG at mailman.qth.net
>>>>
>>>>     This list hosted by:
>>>>     https://www.qsl.net
>>>>     Please help support this email list:
>>>>     https://www.qsl.net/donate.html
>>>     ______________________________________________________________
>>>     600MRG mailing list
>>>     Home: http://mailman.qth.net/mailman/listinfo/600mrg
>>>     <http://mailman.qth.net/mailman/listinfo/600mrg>
>>>     Help: http://mailman.qth.net/mmfaq.htm
>>>     <http://mailman.qth.net/mmfaq.htm>
>>>     Post: mailto:600MRG at mailman.qth.net <mailto:600MRG at mailman.qth.net>
>>>
>>>     This list hosted by: https://www.qsl.net <https://www.qsl.net/>
>>>     Please help support this email list:
>>>     https://www.qsl.net/donate.html <https://www.qsl.net/donate.html>
>>
>>     73, Ed - KL7UW
>>     http://www.kl7uw.com
>>     <http://www.kl7uw.com/>Dubus-NA Business mail:
>>     dubususa at gmail.com <mailto:dubususa at gmail.com>
>>
>     ______________________________________________________________
>     600MRG mailing list
>     Home: http://mailman.qth.net/mailman/listinfo/600mrg
>     Help: http://mailman.qth.net/mmfaq.htm
>     Post: mailto:600MRG at mailman.qth.net <mailto:600MRG at mailman.qth.net>
>
>     This list hosted by: https://www.qsl.net
>     Please help support this email list: https://www.qsl.net/donate.html
>
>
>
> -- 
> K1FZY (WA4TPW) SK  9/29/37-4/13/15
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/600mrg/attachments/20191211/d1945365/attachment.html>

More information about the 600MRG mailing list