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RG-400 vs. RG-142

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jpx(at)Qenesis.com
Guest

Posted: Thu Mar 06, 2008 10:10 am Post subject: RG-400 vs. RG-142

From: "Robert L. Nuckolls, III" <nuckolls.bob(at)cox.net>

    Consider a 10' run of coax from GPS receiver

    to antenna. RG58 offers an attenuation of about

    35db/100'; RG-400/142 is about 24db/100'.

    10' runs reduce to 3.5 and 2.4 db for a difference

    of 1.3 db . . . delta that is impossible to

    observe and difficult to measure at that frequency.



    With respect to materials,  RG-400/142 are double-

    layer, silver-plated shield and fabricated from

    modern cousins to Teflon. It's the best we know how

    to do  . . . today.



What do you think about Andrew FSJ1RN-50B Heliax Cable ?



At 150MHz the attenuation is only 2.2 dB/100'

The minimum bend radius is only 1" and it doesn't try to unbend itself  

due to the corrugated shield.

It is more expensive of course, plus you need their expensive BNC connectors.



http://www.andrew.com/catalog/product_details.aspx?id=1343



Jeff Page

Dream Aircraft Tundra #10

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nuckolls.bob(at)cox.net
Guest

Posted: Thu Mar 06, 2008 11:36 am Post subject: RG-400 vs. RG-142

At 01:06 PM 3/6/2008 -0500, you wrote:



 	  Quote: 	
		  



From: "Robert L. Nuckolls, III" <nuckolls.bob(at)cox.net>

    Consider a 10' run of coax from GPS receiver

    to antenna. RG58 offers an attenuation of about

    35db/100'; RG-400/142 is about 24db/100'.

    10' runs reduce to 3.5 and 2.4 db for a difference

    of 1.3 db . . . delta that is impossible to

    observe and difficult to measure at that frequency.



    With respect to materials,  RG-400/142 are double-

    layer, silver-plated shield and fabricated from

    modern cousins to Teflon. It's the best we know how

    to do  . . . today.



What do you think about Andrew FSJ1RN-50B Heliax Cable ?



At 150MHz the attenuation is only 2.2 dB/100'

The minimum bend radius is only 1" and it doesn't try to unbend itself

due to the corrugated shield.

It is more expensive of course, plus you need their expensive BNC connectors.



http://www.andrew.com/catalog/product_details.aspx?id=1343


	


   There are MANY alternative coax products that

   would reduce losses in the antenna's feedline.

   But what's the return on investment? The as-installed

   performance differences for having utilized some form

   of super-coax would be difficult to measure, much less

   observe.



   Bob . . .

        ----------------------------------------)

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

        ----------------------------------------

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jetboy

Joined: 22 Jul 2006
Posts: 233

Posted: Thu Mar 06, 2008 1:11 pm Post subject: Re: RG-400 vs. RG-142

I'm up to my elbows on a daily basis in FSJ1-50 and the larger family of heliax up to 3" dia.



They are unsuitable for aircraft use due to weight and flexibility. Especially the end connections which do not tolerate much post - install stress.



The cables Bob has replied are the best for the purpose, besides, transponders and radios are designed to operate with some cable loss and in fact you  will have a harder time getting a satisfactory match over the VHF band if your cable is too good. Then you have to start re-engineering and / or ferrite loading the antenna system.



Be sure to use good connectors, not the computer - grade variety. Connectors improperly installed cause more problems than the cable.



Ralph

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_________________
Ralph - CH701 / 2200a

bbradburry(at)bellsouth.n
Guest

Posted: Thu Mar 06, 2008 2:21 pm Post subject: RG-400 vs. RG-142

I installed my transponder antenna about 6 months ago in the rear of my

plane.  Now I am getting ready to install the transponder itself.  While

reading the instructions, I discovered that the max distance for RG400 is

8.8 feet.  My installation is probably 10 feet.  Do I need to move the

antenna?  If I don't move it, what will be the down side?  It is a Garmin

GTX327 if that matters..



Bill B 



--

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klehman(at)albedo.net
Guest

Posted: Thu Mar 06, 2008 7:22 pm Post subject: RG-400 vs. RG-142

I think I asked the same question awhile ago Bill but 11 feet seems to 

work fine on a GTX320 despite the 8.8 foot caution.

Ken



Bill Bradburry wrote:

 	  Quote: 	
		   

 

 I installed my transponder antenna about 6 months ago in the rear of my

 plane.  Now I am getting ready to install the transponder itself.  While

 reading the instructions, I discovered that the max distance for RG400 is

 8.8 feet.  My installation is probably 10 feet.  Do I need to move the

 antenna?  If I don't move it, what will be the down side?  It is a Garmin

 GTX327 if that matters..

 

 Bill B

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nuckolls.bob(at)cox.net
Guest

Posted: Fri Mar 07, 2008 7:07 am Post subject: RG-400 vs. RG-142

At 10:19 PM 3/6/2008 -0500, you wrote:



 	  Quote: 	
		  



I think I asked the same question awhile ago Bill but 11 feet seems to 

work fine on a GTX320 despite the 8.8 foot caution.

Ken



Bill Bradburry wrote:

>

><bbradburry(at)bellsouth.net>

>I installed my transponder antenna about 6 months ago in the rear of my

>plane.  Now I am getting ready to install the transponder itself.  While

>reading the instructions, I discovered that the max distance for RG400 is

>8.8 feet.  My installation is probably 10 feet.  Do I need to move the

>antenna?  If I don't move it, what will be the down side?  It is a Garmin

>GTX327 if that matters..

>Bill B


	


     When a manufacturer publishes performance specifications

     for a product, they need to state the boundaries on installation

     variables that influence the numbers.



     In the case of 8.8' max length, they're only saying that

     performance will be degraded from the published specifications

     if that length is exceeded. What is not so apparent is

     whether or not a user/observer would be aware of the

     degradation . . . and in this case, the answer is no.



     There's enough head-room in the receiver's capability to

     deliver useful performance in spite of an additional 0.1

     Db or so of feedline losses.



     Now, if you were installing this radio in a 787 and needed

     to put the antenna out on a wing tip, a higher performance

     coax cable would be a really good idea.



     Bob . . .



        ----------------------------------------)

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

        ----------------------------------------

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