[600MRG] Coax shielding effectiveness

[Gedas]

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 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
>
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