[600MRG] Coax shielding effectiveness
Gedas
w8bya at mchsi.com
Thu Dec 12 10:35:57 EST 2019
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
> <mailto: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 athttp://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) SKÂ 9/29/37-4/13/15
>>>>>
>>>>>
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>>>
>>> 73, Ed - KL7UW
>>> http://www.kl7uw.com
>>> <http://www.kl7uw.com/>Dubus-NA Business mail:
>>> dubususa at gmail.com <mailto:dubususa at gmail.com>
>>>
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>> --
>> K1FZY (WA4TPW) SK 9/29/37-4/13/15
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