[600MRG] Coax shielding effectiveness

Thu Dec 12 10:55:10 EST 2019

Indeed.  I have some 214 cables on order. I am still looking for the
supershield as the transfer impedance is supposed to be four orders of
magnitude lower than the fsj.

On Thu, Dec 12, 2019, 8:38 AM Gedas <w8bya at mchsi.com> wrote:

> Flexibility was not the only reason I liked the RG-214 over the FSJ1-50.
> At low frequencies (below several MHz) it has a higher SE and when used
> with quality N-connectors (like an Amphenol crimp style properly installed)
> will provide less leakage and a better termination at the ends of the
> cable. In my prior life doing tempest work ultra-high isolation, SE, and
> the ability to spot "snakes in the grass" was the name of the game. At
> higher frequencies there are better choices but I assumed you were
> interested in VLF since you posted here.
>
> 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 12/12/2019 9:03 AM, david vanhorn wrote:
>
> 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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