[600MRG] Coax shielding effectiveness

Thu Dec 12 09:03:09 EST 2019

I'm not too worried about flexibility, I can sculpt the cables to fit and
then they won't need to be moved again.
RG-214 might be my backup plan, if I can't locate this "supershield" cable.
I'm just trying to remove unnecessary variables in my measurements.

On Wed, Dec 11, 2019 at 8:16 AM Gedas <w8bya at mchsi.com> wrote:

> 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> 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 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 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 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.Â
>> I'm not seeing anything talking much below 100MHz.
>>
>> Can someone point me in the right direction?
>>
>> --
>> K1FZY (WA4TPW) SKÂ  9/29/37-4/13/15
>>
>>
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>> 73, Ed - KL7UW
>>   http://www.kl7uw.com
>> Dubus-NA Business mail:
>>   dubususa at gmail.com
>>
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>
>
> --
> K1FZY (WA4TPW) SK  9/29/37-4/13/15
>
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-- 
K1FZY (WA4TPW) SK  9/29/37-4/13/15
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