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GPS antennas with miniature connector

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trigo(at)mail.telepac.pt
Guest

Posted: Mon May 12, 2008 6:07 am Post subject: GPS antennas with miniature connector

Listers



I have 2 GPS antennas to install, one is for my Trutrak ADI and the other

for the GRT - EFIS, both having internal GPS.

I attached 2 pictures of one of them, they are similar, both use a thin

cable (less than 1/8" outer diameter) and a miniature brass connector.



Since we must always seek to save some weight in our birds, I have 2

questions:



First question, which is probably dumb, but here it goes: can I install only

one antenna and T the cable for both devices?



Second question: if I want to get rid of that much cable length, can I cut

it somewhere in the middle, remove the unnecessary length, and reconnect the

cable ends? If yes, how do I do it?

Or is it better to forget the existing connector, cut the necessary length

and use a new connector? In this case, where can I find these miniature

connectors and is there a special crimper for these?



Carlos Trigo

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echristley(at)nc.rr.com
Guest

Posted: Mon May 12, 2008 7:36 am Post subject: GPS antennas with miniature connector

Carlos Trigo wrote:

 	  Quote: 	
		   Listers



 I have 2 GPS antennas to install, one is for my Trutrak ADI and the other

 for the GRT - EFIS, both having internal GPS.

 I attached 2 pictures of one of them, they are similar, both use a thin

 cable (less than 1/8" outer diameter) and a miniature brass connector.



 Since we must always seek to save some weight in our birds, I have 2

 questions:



 First question, which is probably dumb, but here it goes: can I install only

 one antenna and T the cable for both devices?

   

Yes.  You'll just have to fly much closer to the satellites in order to 
	


get sufficient signal strength to get a lock.  Remember that those 

satellites are REALLY far away (22,500 miles ?), which means your 

receiver has to capture a very weak signal.  Cutting the received signal 

in half isn't going to be helpful.

 	  Quote: 	
		   Second question: if I want to get rid of that much cable length, can I cut

 it somewhere in the middle, remove the unnecessary length, and reconnect the

 cable ends? If yes, how do I do it?

 Or is it better to forget the existing connector, cut the necessary length

 and use a new connector? In this case, where can I find these miniature

 connectors and is there a special crimper for these?

   

That can be done, but you're trading a crimp done constantly by a 
	


machine that has some semblance of quality control for a one-off job 

done by someone that (so far) doesn't even know which crimper to use.  

You could eventually do a better job than the machine.  The question is 

if the weight savings are worth the expense and effort. 



I suggest you weigh that 1/8" cable and then decide if it is worth your 

effort.  I you think it is, then try splitting it then see how many 

satellites it the receiver will lock onto.  The ones to watch for are 

the ones on the horizons, as they will be giving the weakest signals.

trigo(at)mail.telepac.pt
Guest

Posted: Mon May 12, 2008 8:20 am Post subject: GPS antennas with miniature connector

Dear Ernest



Although you were not of much help, thanks anyway.

If I didn't think it was worth the effort to save the weight, I wouldn't

have asked.



Can somebody else please indicate me a way of getting rid of those 2 useless

coils of GPS antenna cable?



Carlos

[quote] --

simon(at)synchronousdesig
Guest

Posted: Mon May 12, 2008 9:16 am Post subject: GPS antennas with miniature connector

 	  Quote: 	
		   First question, which is probably dumb, but here it goes: can I

 install only one antenna and T the cable for both devices?


	


Carlos, GPS satellites transmit very weak signals, and most GPS receivers

are designed to get as much signal strength as possible for best

reliability.  Putting a T between the antennas and the receiver will

guarantee failure or at best, lousy performance.  By the way, GPS

satellites are not 22,500 miles out.  That radius would put them in

synchronous orbit with the TV and other satellites.  Instead, they are

12,500 miles out and orbit north to south.  The transmitters' output

powers guarantee weak signals by the time they make it into our

atmosphere.  The best solution is to provide a dedicated GPS amtenna for

each receiver.



 	  Quote: 	
		   Second question: if I want to get rid of that much cable length,

 can I cut it somewhere in the middle, remove the unnecessary

 length, and reconnect the cable ends? If yes, how do I do it?

 Or is it better to forget the existing connector, cut the

 necessary length and use a new connector? In this case, where

 can I find these miniature connectors and is there a special

 crimper for these?


	


Again, any tampering with the cable between the antenna and the receiver

will introduce attenuation.  There is a good solution here, though. 

Instead of cutting it in the middle, just cut it to length and then place

the same type connector on the cut end.  You may have to buy special

tooling to do this, but if you really want to do it and you do it right,

you will not suffer signal degradation.  All connectors introduce some

degradation, but all you're doing is moving the degradation from N feet

out to N/2 feet out.



Simon Ramirez

Oviedo, FL  USA

mprather(at)spro.net
Guest

Posted: Mon May 12, 2008 9:53 am Post subject: GPS antennas with miniature connector

Aren't many GPS antennas active (amplified, powered)?  If so, it should be

possible to design an impedance match circuit from the output of the

antenna to the input of the two receivers.  It's also possible that the

output of the amplified antenna is robust enough to not require any match

circuitry for adequate performance...

Regards,



Matt-



 	  Quote: 	
		   



> First question, which is probably dumb, but here it goes: can I

> install only one antenna and T the cable for both devices?



 Carlos, GPS satellites transmit very weak signals, and most GPS receivers

 are designed to get as much signal strength as possible for best

 reliability.  Putting a T between the antennas and the receiver will

 guarantee failure or at best, lousy performance.  By the way, GPS

 satellites are not 22,500 miles out.  That radius would put them in

 synchronous orbit with the TV and other satellites.  Instead, they are

 12,500 miles out and orbit north to south.  The transmitters' output

 powers guarantee weak signals by the time they make it into our

 atmosphere.  The best solution is to provide a dedicated GPS amtenna for

 each receiver.



> Second question: if I want to get rid of that much cable length,

> can I cut it somewhere in the middle, remove the unnecessary

> length, and reconnect the cable ends? If yes, how do I do it?

> Or is it better to forget the existing connector, cut the

> necessary length and use a new connector? In this case, where

> can I find these miniature connectors and is there a special

> crimper for these?



 Again, any tampering with the cable between the antenna and the receiver

 will introduce attenuation.  There is a good solution here, though.

 Instead of cutting it in the middle, just cut it to length and then place

 the same type connector on the cut end.  You may have to buy special

 tooling to do this, but if you really want to do it and you do it right,

 you will not suffer signal degradation.  All connectors introduce some

 degradation, but all you're doing is moving the degradation from N feet

 out to N/2 feet out.



 Simon Ramirez

 Oviedo, FL  USA

jdubner(at)yahoo.com
Guest

Posted: Mon May 12, 2008 10:09 am Post subject: GPS antennas with miniature connector

On 05/12/2008 09:14 Carlos Trigo wrote:

 	  Quote: 	
		   

 

 Can somebody else please indicate me a way of getting rid of those 2 useless

 coils of GPS antenna cable?


	


Carlos,



I had a similar dilemma a few years ago and decided to retain the

connector rather than install a new one.  I cut the cable near the

connector, cut the antenna end of the cable to the desired length, and

spliced the two pieces of the cable back together.  This is also a

viable technique if you need to "temporarily" remove the connector for

cable routing through a small conduit or to lengthen the cable.



The pundits will tell you that you can't splice this coax as it carries

a very weak 1.575 GHz signal but I never noticed any degradation in the

performance of the GPS.



Of course, I paid attention to detail in the splice by keeping the

splice length to a minimum, re-insulating the center conductor well, and

then restoring the shield coverage to as near 100% as possible.



Best,

Joe

Long-EZ 821RP

Lewiston, ID

nuckolls.bob(at)cox.net
Guest

Posted: Mon May 12, 2008 10:46 am Post subject: GPS antennas with miniature connector

At 03:04 PM 5/12/2008 +0100, you wrote:



 	  Quote: 	
		  Listers



I have 2 GPS antennas to install, one is for my Trutrak ADI and the other

for the GRT - EFIS, both having internal GPS.

I attached 2 pictures of one of them, they are similar, both use a thin

cable (less than 1/8" outer diameter) and a miniature brass connector.



Since we must always seek to save some weight in our birds, I have 2

questions:



First question, which is probably dumb, but here it goes: can I install only

one antenna and T the cable for both devices?


	


   No, for a couple of reasons. One is that this antenna . . .



http://www.laipac.com/ant_GLP1_RA_eng.htm



   is a powered device that gets its operating voltage from the

   associated GPS receiver. Mixing two receivers onto a single

   antenna offers some system integration as well as some

   system reliability (single point of failure for both

   receivers) issues. Recommend you stick with dual antennas.



 	  Quote: 	
		  Second question: if I want to get rid of that much cable length, can I cut

it somewhere in the middle, remove the unnecessary length, and reconnect the

cable ends? If yes, how do I do it?

Or is it better to forget the existing connector, cut the necessary length

and use a new connector? In this case, where can I find these miniature

connectors and is there a special crimper for these?


	


  From the photos, I deduce that your antennas are fitted with

  the SMB series connectors. But these come in several styles that

  include screw on and push-on. It looks like you have the

  push-on style.



http://www.aeroelectric.com/Pictures/Connectors/Coax/SMB_push-on_1.jpg

http://www.aeroelectric.com/Pictures/Connectors/Coax/SMB_push-on_2.jpg

http://www.aeroelectric.com/Pictures/Connectors/Coax/SMB_push-on_3.jpg



  Digikey sells these connectors but a quick look for tools

  did not produce any hits.



  The task of shortening these cables is trivial

  for anyone with the skills, tools and connectors. You

  may be able to find someone locally who routinely works

  with these connectors and get the job done.



  However, keep in mind that the antenna assembly's performance

  IS BASED on the as-supplied condition . . . meaning that it

  will perform as advertised with the long cables. It's

  doubtful that you'll improve on that performance in any

  way that you can perceived so this leaves you with the

  goal of shortening the cables because it looks better

  and saves a little weight.



  Obviously we need to leave it to you to deduce the

  trade-off for accepting the costs and risks for a

  DIY cable shortening effort and the return on

  investment for achieving a slicker looking installation

  and a few ounces of weight.



  My best recommendation is that (unless you can find

  some local support in skills/materials/tools) you

  leave them as supplied.

        Bob . . .



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

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

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

simon(at)synchronousdesig
Guest

Posted: Mon May 12, 2008 10:49 am Post subject: GPS antennas with miniature connector

Matt,



If his GPS antenna is powered by the receivers, then a T no doubt will

interfere with that function, as DC doesn't pass through transformers.  If

Carlos can give us more details pertaining to the specific antenna and GPS

receiver models, then his problem can be analyzed further.



Joe Dubner earlier said he spliced his GPS antenna cable in the middle,

and it performed well.  I am surprised, but I've seen stranger stuff

happen.  I'd rather remove the connector, cut the cable, run it through

the small opening, and reinstall a new connector.



Simon

Oviedo, FL  USA

 	  Quote: 	
		   

 <mprather(at)spro.net>



 Aren't many GPS antennas active (amplified, powered)?  If so, it

 should be possible to design an impedance match circuit from the

 output of the antenna to the input of the two receivers.  It's

 also possible that the output of the amplified antenna is robust

 enough to not require any match circuitry for adequate

 performance...



 Regards,



 Matt-

mprather(at)spro.net
Guest

Posted: Mon May 12, 2008 11:41 am Post subject: GPS antennas with miniature connector

Right..  You'd have to admit though that it wouldn't be rocket science to

make 5VDC available to the antenna - from the antenna side of the matcher.



Then again, I'd likely try to find antennae that's smaller/lighter, and

with shorter cables..

Matt-



 	  Quote: 	
		   



 Matt,



 If his GPS antenna is powered by the receivers, then a T no doubt will

 interfere with that function, as DC doesn't pass through transformers.  If

 Carlos can give us more details pertaining to the specific antenna and GPS

 receiver models, then his problem can be analyzed further.



 Joe Dubner earlier said he spliced his GPS antenna cable in the middle,

 and it performed well.  I am surprised, but I've seen stranger stuff

 happen.  I'd rather remove the connector, cut the cable, run it through

 the small opening, and reinstall a new connector.



 Simon

 Oviedo, FL  USA

> 

> <mprather(at)spro.net>

>

> Aren't many GPS antennas active (amplified, powered)?  If so, it

> should be possible to design an impedance match circuit from the

> output of the antenna to the input of the two receivers.  It's

> also possible that the output of the amplified antenna is robust

> enough to not require any match circuitry for adequate

> performance...

>

> Regards,

>

> Matt-

simon(at)synchronousdesig
Guest

Posted: Mon May 12, 2008 12:33 pm Post subject: GPS antennas with miniature connector

Matt,



I admit it is not rocket science to provide DC voltage if you have the

source and delivery system for it.  In Carlos' case, though, I believe his

goal was to squeeze nano-tons of weight out of whatever he was doing, and

an additional wire from one receiver or power supply to the antenna would

defeat this purpose.  He might as well stay with the extra cable length.



In an earlier email, Bob said that two receivers supplying VDC will

introduce further complications, and one antenna feeding two receivers is

a single-failure point.  These two statements are valid.  If two GPS

receivers were going into my airplane, I would have two separate antennas.

 Of course, I'm not as worried about weight as Carlos is either.  I know a

guy who wants to cross the Atlantic in July and August, and he's in the

same "bloat."



Simon

Oviedo, FL  USA

 	  Quote: 	
		   Right..  You'd have to admit though that it wouldn't be rocket science to

 make 5VDC available to the antenna - from the antenna side of the matcher.



 Then again, I'd likely try to find antennae that's smaller/lighter, and

 with shorter cables..



 Matt-

trigo(at)mail.telepac.pt
Guest

Posted: Mon May 12, 2008 1:50 pm Post subject: GPS antennas with miniature connector

OK, I surrender. I will use 2 antennas and keep those lengthy cables.

A 3 month diet will save weight on myself, which seems easier (apart from

being better for my health).



Thanks to everybody who answered.

Carlos

Mark Phillips in TN

Joined: 10 Jan 2006
Posts: 431
Location: Columbia, TN

Posted: Mon May 12, 2008 6:02 pm Post subject: GPS antennas with miniature connector

In a message dated 05/12/2008 12:18:32 PM Central Daylight Time, simon(at)synchronousdesign.com writes:

  	  Quote: 	
		  > Second question: if I want to get rid of that much cable length, 	

 >>>

 I recently installed a Garmin 430W (WAAS) that has a dedicated GPS antenna with a "required" MINIMUM cable length of something like 18 FEET.  Being a "certified" navcom, I kinda surmised that Garmin requires this because they have to make sure there is sufficient signal strength getting to the receiver.  

 Huh?  

 Picture a 430W installed in a King Air with the antenna halfway aft on the top of the fuse- might take 30-40' of cable to connect the two.  Using the same certified antenna for all certified installations, how does a manufacturer offer a unit that ALSO works in Katanas?  By making sure the signal strength is sufficient for either installation, hence the minumum/maximum cable length for which the unit is guaranteed it will work.  

 Really wanting to avoid wadding up an extra 15 feet of RG400, I called Garmin tech and they confirmed my theory.  If I had shortened the cable to a convenient minimun length (about 3") the signal would have been too powerful for the receiver due to insufficient attenuation.  OK, but how about shortening the cable and adding an attenuator, being on an experimental.  The guy basically said fine, but you're on your own!  After a couple of hours researching this option and coming up with no simple answers, I decided the path of  least resistance was to do as instructed.  I wadded up the extra 15 feet of RG400, and the sucker works just great.  Still got a warranty, too! Win-win!

 I'd guess you have the same situation with the smaller GPS antennas(ae?) and that is why they come with all that extra cable.  Just wad it up (like I did for the GRT & ADI GPS & XM cables) and be glad it ain't RG400!

 Mark

Wondering what's for Dinner Tonight? Get new twists on family favorites at AOL Food.

  [quote][b]

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