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BNC connectors and SWR

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fvalarm(at)rapidnet.net
Guest

Posted: Wed Mar 16, 2016 9:51 pm Post subject: BNC connectors and SWR

I am  considering moving a VHF Comm antenna to the upper rear fuselage of the  RV7, requiring a longer feed cable.    To do this, I will make an  extension cable which will result in two additional BNC connectors  which will result in two BNC's (male and female) be located mid stream in the  new antenna feed cable.

  

 My  questions are...

  

 Will  these two additional connectors significantly increase the SWR and have a  negative affect on the radio's health over time?

  

 Will  these BNC junctions bundled with other wires "leak" any RF from the BNC joint  that will effect other systems?

  

 Should  I just run a new cable thereby eliminating the junction?

  

 Thanks.

  

 Bevan

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user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Fri Mar 18, 2016 5:09 am Post subject: Re: BNC connectors and SWR

Since nobody else has replied, I will give my opinion which is only based reading these forums.

No, the BNC connector splice will not affect SWR.

No, RF will not leak from this BNC spice.

Should a new cable be run: maybe.  Anytime wires are spliced, a potential trouble spot is created.  If the spice is readily and easily accessible for future inspection and troubleshooting, then OK, splice on additional cable.  On the other hand, if you want peace of mind and less chance of future problems, replace the cable.  RG400 or RG142 is better than RG58.

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_________________
Joe Gores

rv10pro(at)gmail.com
Guest

Posted: Fri Mar 18, 2016 6:27 am Post subject: BNC connectors and SWR

Affirmative to each of the above points.  However each connector introduces additional db loss which will degrade transmission and to a lesser extent reception.  Don't cut the corner.  Run a new cable run.  We have fits with four cable runs to upper TCAS antenna and especially lower runs.  8 cables are a bitch and the central failure point in the absence of lighning strikes directly with the Antenna.



John Cox

Avionics Tech

On Fri, Mar 18, 2016 at 6:09 AM, user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:

 	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

 

 Since nobody else has replied, I will give my opinion which is only based reading these forums.

 No, the BNC connector splice will not affect SWR.

 No, RF will not leak from this BNC spice.

 Should a new cable be run: maybe.  Anytime wires are spliced, a potential trouble spot is created.  If the spice is readily and easily accessible for future inspection and troubleshooting, then OK, splice on additional cable.  On the other hand, if you want peace of mind and less chance of future problems, replace the cable.  RG400 or RG142 is better than RG58.

 

 --------

 Joe Gores

 

 

 

 

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ceengland7(at)gmail.com
Guest

Posted: Fri Mar 18, 2016 8:28 am Post subject: BNC connectors and SWR

You're technically correct. 



But run the numbers to see if the degradation is enough to justify the hassle of re-running an existing cable. The original post didn't make it into this post, but if he's talking SWR, he's probably talking about a comm; not a gigahertz range radio. How much range loss is there for 0.2 dB insertion loss when a typical max *needed* range is maybe 30 miles? 1/2 mile? 1/10 mile? 50 feet?



The reliability issue remains, but in my experience, cutting into wire bundles all over the plane to extract the old cable and run a new one introduces many more and greater risks.

Another perspective...



On Fri, Mar 18, 2016 at 9:26 AM, John Cox <rv10pro(at)gmail.com (rv10pro(at)gmail.com)> wrote:

 	  Quote: 	
		  Affirmative to each of the above points.  However each connector introduces additional db loss which will degrade transmission and to a lesser extent reception.  Don't cut the corner.  Run a new cable run.  We have fits with four cable runs to upper TCAS antenna and especially lower runs.  8 cables are a bitch and the central failure point in the absence of lighning strikes directly with the Antenna.



John Cox

Avionics Tech

On Fri, Mar 18, 2016 at 6:09 AM, user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:

 	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

 

 Since nobody else has replied, I will give my opinion which is only based reading these forums.

 No, the BNC connector splice will not affect SWR.

 No, RF will not leak from this BNC spice.

 Should a new cable be run: maybe.  Anytime wires are spliced, a potential trouble spot is created.  If the spice is readily and easily accessible for future inspection and troubleshooting, then OK, splice on additional cable.  On the other hand, if you want peace of mind and less chance of future problems, replace the cable.  RG400 or RG142 is better than RG58.

 

 --------

 Joe Gores

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Kellym

Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ

Posted: Fri Mar 18, 2016 8:56 am Post subject: BNC connectors and SWR

That is one of the great trade-offs, difficulty vs quality 

communications. A good com(6-8 watts), with good cable and good 

antenna/ground plane can communicate over at least 50 nm or more. Very 

important in some parts of the West, especially IFR.



On 3/18/2016 9:25 AM, Charlie England wrote:

 	  Quote: 	
		   You're technically correct.



 But run the numbers to see if the degradation is enough to justify the

 hassle of re-running an existing cable. The original post didn't make it

 into this post, but if he's talking SWR, he's probably talking about a

 comm; not a gigahertz range radio. How much range loss is there for 0.2

 dB insertion loss when a typical max *needed* range is maybe 30 miles?

 1/2 mile? 1/10 mile? 50 feet?



 The reliability issue remains, but in my experience, cutting into wire

 bundles all over the plane to extract the old cable and run a new one

 introduces many more and greater risks.



 Another perspective...



 On Fri, Mar 18, 2016 at 9:26 AM, John Cox <rv10pro(at)gmail.com

 <mailto:rv10pro(at)gmail.com>> wrote:



     Affirmative to each of the above points.  However each connector

     introduces additional db loss which will degrade transmission and to

     a lesser extent reception.  Don't cut the corner.  Run a new cable

     run.  We have fits with four cable runs to upper TCAS antenna and

     especially lower runs.  8 cables are a bitch and the central failure

     point in the absence of lighning strikes directly with the Antenna.



     John Cox

     Avionics Tech



     On Fri, Mar 18, 2016 at 6:09 AM, user9253 <fransew(at)gmail.com

     <mailto:fransew(at)gmail.com>> wrote:



         

         <fransew(at)gmail.com <mailto:fransew(at)gmail.com>>



         Since nobody else has replied, I will give my opinion which is

         only based reading these forums.

         No, the BNC connector splice will not affect SWR.

         No, RF will not leak from this BNC spice.

         Should a new cable be run: maybe.  Anytime wires are spliced, a

         potential trouble spot is created.  If the spice is readily and

         easily accessible for future inspection and troubleshooting,

         then OK, splice on additional cable.  On the other hand, if you

         want peace of mind and less chance of future problems, replace

         the cable.  RG400 or RG142 is better than RG58.



         --------

         Joe Gores

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_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD

ceengland7(at)gmail.com
Guest

Posted: Fri Mar 18, 2016 9:39 am Post subject: BNC connectors and SWR

Fine; call it 70 miles. Run the numbers.



On 3/18/2016 11:54 AM, Kelly McMullen wrote:

 	  Quote: 	
		   

 <kellym(at)aviating.com>



 That is one of the great trade-offs, difficulty vs quality 

 communications. A good com(6-8 watts), with good cable and good 

 antenna/ground plane can communicate over at least 50 nm or more. Very 

 important in some parts of the West, especially IFR.



 On 3/18/2016 9:25 AM, Charlie England wrote:

> You're technically correct.

>

> But run the numbers to see if the degradation is enough to justify the

> hassle of re-running an existing cable. The original post didn't make it

> into this post, but if he's talking SWR, he's probably talking about a

> comm; not a gigahertz range radio. How much range loss is there for 0.2

> dB insertion loss when a typical max *needed* range is maybe 30 miles?

> 1/2 mile? 1/10 mile? 50 feet?

>

> The reliability issue remains, but in my experience, cutting into wire

> bundles all over the plane to extract the old cable and run a new one

> introduces many more and greater risks.

>

> Another perspective...

>

> On Fri, Mar 18, 2016 at 9:26 AM, John Cox <rv10pro(at)gmail.com

> <mailto:rv10pro(at)gmail.com>> wrote:

>

>     Affirmative to each of the above points.  However each connector

>     introduces additional db loss which will degrade transmission and to

>     a lesser extent reception.  Don't cut the corner.  Run a new cable

>     run.  We have fits with four cable runs to upper TCAS antenna and

>     especially lower runs.  8 cables are a bitch and the central failure

>     point in the absence of lighning strikes directly with the Antenna.

>

>     John Cox

>     Avionics Tech

>

>     On Fri, Mar 18, 2016 at 6:09 AM, user9253 <fransew(at)gmail.com

>     <mailto:fransew(at)gmail.com>> wrote:

>

>         

>         <fransew(at)gmail.com <mailto:fransew(at)gmail.com>>

>

>         Since nobody else has replied, I will give my opinion which is

>         only based reading these forums.

>         No, the BNC connector splice will not affect SWR.

>         No, RF will not leak from this BNC spice.

>         Should a new cable be run: maybe.  Anytime wires are spliced, a

>         potential trouble spot is created.  If the spice is readily and

>         easily accessible for future inspection and troubleshooting,

>         then OK, splice on additional cable.  On the other hand, if you

>         want peace of mind and less chance of future problems, replace

>         the cable.  RG400 or RG142 is better than RG58.

>

>         --------

>         Joe Gores

>

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