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Minimum GPS Antenna Cable Length

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user9253

Joined: 28 Mar 2008
Posts: 1931
Location: Riley TWP Michigan

Posted: Thu Mar 30, 2017 3:01 am Post subject: Minimum GPS Antenna Cable Length

I am installing an Appareo Stratus ESG transponder with internal GPS.  It did not come with antenna cables.  I purchased a 19 inch RG400 GPS antenna cable before reading the installation directions which state, "All wiring should have a cable loss of minimum 2 dB . . . .Using RG400 the minimum cable length is 10 feet".

  Will the GPS work satisfactorily with the short cable?  If not, what is a cheap and easy way to increase the dB loss?  What is the theory behind the requirement for at least 2 dB cable loss?

_________________
Joe Gores

sharmon32(at)juno.com
Guest

Posted: Thu Mar 30, 2017 4:12 am Post subject: Minimum GPS Antenna Cable Length

I also installed an Appereo in my cozy I called the factory they said you need at least 10 foot of antenna cable so you have some resistance my antenna is 2 ft. From the stratus they told me to just roll up the extra so that is what I did .   It. Works who am I to argue with success.

Steve build on 



Sent from my iPad



 	  Quote: 	
		   On Mar 30, 2017, at 5:01 AM, user9253 <fransew(at)gmail.com> wrote:

 

 

 

 I am installing an Appareo Stratus ESG transponder with internal GPS.  It did not come with antenna cables.  I purchased a 19 inch RG400 GPS antenna cable before reading the installation directions which state, "All wiring should have a cable loss of minimum 2 dB . . . .Using RG400 the minimum cable length is 10 feet".

  Will the GPS work satisfactorily with the short cable?  If not, what is a cheap and easy way to increase the dB loss?  What is the theory behind the requirement for at least 2 dB cable loss?

 

 --------

 Joe Gores

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=467824#467824

 

 

 

 

 

 

 

 

 

 


	


____________________________________________________________

This Simple Step To Flawless Skin

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ceengland7(at)gmail.com
Guest

Posted: Thu Mar 30, 2017 5:12 am Post subject: Minimum GPS Antenna Cable Length

On Thu, Mar 30, 2017 at 6:01 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)>

 

 I am installing an Appareo Stratus ESG transponder with internal GPS.  It did not come with antenna cables.  I purchased a 19 inch RG400 GPS antenna cable before reading the installation directions which state, "All wiring should have a cable loss of minimum 2 dB . . . .Using RG400 the minimum cable length is 10 feet".

   Will the GPS work satisfactorily with the short cable?  If not, what is a cheap and easy way to increase the dB loss?  What is the theory behind the requirement for at least 2 dB cable loss?

 

 --------

 Joe Gores

 

	




The 1st thing that comes to mind is this. Most radio receivers have multiple gain stages (in addition to frequency down-conversions) to get weak RF signals up to a level that's useful. Each gain stage will typically have automatic gain control (AGC) that prevents the amplifier from being driven into distortion by a too-strong input signal. But there's a limit to the range of AGC. They've probably calculated the max possible output from the GPS puck (which probably has both the 1st frequency downconversion and gain), and the cable loss prevents overdriving the 1st gain stage in the box.

When the GPS RF signal is weaker, the box's AGC circuit can ramp up gain to compensate.

If you ever fly formation, you might hear the same overdrive effect in your comm radio. The wingman's radio might sound fine until they get within a half mile or so, but as they get closer, their audio sounds fuzzy & garbled. When they break formation & move a mile or two away, it clears up again. The bad audio is your radio's AGC being overwhelmed by too much RF or intermediate frequency signal level while the wingman's transmitter is too 'hot' for your receiver to compensate.

Charlie

Kellym

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

Posted: Thu Mar 30, 2017 5:36 am Post subject: Minimum GPS Antenna Cable Length

IIRC each connector in the line adds about 1/2 db of cable loss. So in 

theory, 2 extra adapters in the cable would get you there. Don't know if 

that is exactly correct. So maybe with an extra foot, a union connector 

and 2 BNC connectors, or BNC to TNC adapters and you might have enough 

loss. BTW, BNC to TNC adapter is  lot cheaper than just buying a crimp 

on TNC connector.



On 3/30/2017 4:01 AM, user9253 wrote:

 	  Quote: 	
		   



 I am installing an Appareo Stratus ESG transponder with internal GPS.  It did not come with antenna cables.  I purchased a 19 inch RG400 GPS antenna cable before reading the installation directions which state, "All wiring should have a cable loss of minimum 2 dB . . . .Using RG400 the minimum cable length is 10 feet".

   Will the GPS work satisfactorily with the short cable?  If not, what is a cheap and easy way to increase the dB loss?  What is the theory behind the requirement for at least 2 dB cable loss?



 --------

 Joe Gores





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=467824#467824

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

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Mar 31, 2017 6:19 am Post subject: Minimum GPS Antenna Cable Length

At 06:01 AM 3/30/2017, you wrote:

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



 I am installing an Appareo Stratus ESG transponder with internal GPS.  It did not come with antenna cables.  I purchased a 19 inch RG400 GPS antenna cable before reading the installation directions which state, "All wiring should have a cable loss of minimum 2 dB . . . .Using RG400 the minimum cable length is 10 feet".

   Will the GPS work satisfactorily with the short cable?  If not, what is a cheap and easy way to increase the dB loss?  What is the theory behind the requirement for at least 2 dB cable loss? 	


   I'm having trouble wrapping my head around this

   requirement. GPS satellite signals are exceedingly

   tiny . . . down in the atmospheric noise levels.

   The only reason our tiny wrist-watch, hand-held,

   and self-navigating drones work so well is because

   the 'smarts' in GPS receiver software is looking for

   specific patterns of data in the chaotic patternless

   noise.



   Routine variations in received GPS signals

   is all over the magnitude map spanning perhaps

   tens of db . . . a required 2 db 'addition of 

   attenuation' simply doesn't make sense.



   The idea that a receiver's performance is

   predicated on a minimum of 2db of loss in the

   antenna system by making the cable longer is a

   real puzzle . . . usually, the instructions will

   say something like "limit cable losses to a MAXIMUM

   of 2db where a 10' run of RG-400 is the practical

   limit".



   I'm wondering if this manual wasn't originally crafted

   in Chinese and then translated by some academic instead

   of a systems engineer.



   One thing is for sure, if you install your system

   using only the needed length of coax, you can certainly

   ADD some later. I'm betting a dollar to a dozen doughnuts

   that it will not be necessary. 



 

 

   Bob . . .

Kellym

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

Posted: Fri Mar 31, 2017 6:44 am Post subject: Minimum GPS Antenna Cable Length

Garmin came out with the same requirement when the GNS-430W was 

approved. I believe they later reduced the minimum length to perhaps 6 

ft. I suspect it has more to do with matching the output of the antenna 

pre-amplifier to the main receiver, and doesn't have a lot to do with 

signal strength at all.



On 3/31/2017 7:16 AM, Robert L. Nuckolls, III wrote:

 	  Quote: 	
		   At 06:01 AM 3/30/2017, you wrote:

> 

>

> I am installing an Appareo Stratus ESG transponder with internal GPS.

> It did not come with antenna cables.  I purchased a 19 inch RG400 GPS

> antenna cable before reading the installation directions which state,

> "All wiring should have a cable loss of minimum 2 dB . . . .Using

> RG400 the minimum cable length is 10 feet".

>   Will the GPS work satisfactorily with the short cable?  If not, what

> is a cheap and easy way to increase the dB loss?  What is the theory

> behind the requirement for at least 2 dB cable loss?



   I'm having trouble wrapping my head around this

   requirement. GPS satellite signals are exceedingly

   tiny . . . down in the atmospheric noise levels.

   The only reason our tiny wrist-watch, hand-held,

   and self-navigating drones work so well is because

   the 'smarts' in GPS receiver software is looking for

   specific patterns of data in the chaotic patternless

   noise.



   Routine variations in received GPS signals

   is all over the magnitude map spanning perhaps

   tens of db . . . a required 2 db 'addition of

   attenuation' simply doesn't make sense.



   The idea that a receiver's performance is

   predicated on a minimum of 2db of loss in the

   antenna system by making the cable longer is a

   real puzzle . . . usually, the instructions will

   say something like "limit cable losses to a MAXIMUM

   of 2db where a 10' run of RG-400 is the practical

   limit".



   I'm wondering if this manual wasn't originally crafted

   in Chinese and then translated by some academic instead

   of a systems engineer.



   One thing is for sure, if you install your system

   using only the needed length of coax, you can certainly

   ADD some later. I'm betting a dollar to a dozen doughnuts

   that it will not be necessary.

   Bob . . .

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

Tim Olson

Joined: 25 Jan 2007
Posts: 2879

Posted: Fri Mar 31, 2017 6:55 am Post subject: Minimum GPS Antenna Cable Length

This is not that unusual. My Garman GNS480 had the same requirement.

Keep in mind that the antennas used are active antennas.

Tim



On Mar 31, 2017, at 9:16 AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

 	  Quote: 	
		    At 06:01 AM 3/30/2017, you wrote:

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



 I am installing an Appareo Stratus ESG transponder with internal GPS.  It did not come with antenna cables.  I purchased a 19 inch RG400 GPS antenna cable before reading the installation directions which state, "All wiring should have a cable loss of minimum 2 dB . . . .Using RG400 the minimum cable length is 10 feet".

   Will the GPS work satisfactorily with the short cable?  If not, what is a cheap and easy way to increase the dB loss?  What is the theory behind the requirement for at least 2 dB cable loss? 	


   I'm having trouble wrapping my head around this

   requirement. GPS satellite signals are exceedingly

   tiny . . . down in the atmospheric noise levels.

   The only reason our tiny wrist-watch, hand-held,

   and self-navigating drones work so well is because

   the 'smarts' in GPS receiver software is looking for

   specific patterns of data in the chaotic patternless

   noise.



   Routine variations in received GPS signals

   is all over the magnitude map spanning perhaps

   tens of db . . . a required 2 db 'addition of 

   attenuation' simply doesn't make sense.



   The idea that a receiver's performance is

   predicated on a minimum of 2db of loss in the

   antenna system by making the cable longer is a

   real puzzle . . . usually, the instructions will

   say something like "limit cable losses to a MAXIMUM

   of 2db where a 10' run of RG-400 is the practical

   limit".



   I'm wondering if this manual wasn't originally crafted

   in Chinese and then translated by some academic instead

   of a systems engineer.



   One thing is for sure, if you install your system

   using only the needed length of coax, you can certainly

   ADD some later. I'm betting a dollar to a dozen doughnuts

   that it will not be necessary. 



 

 

   Bob . . .

donvansanten(at)gmail.com
Guest

Posted: Fri Mar 31, 2017 7:01 am Post subject: Minimum GPS Antenna Cable Length

Bob,The first Garmin 430 install manuals stated nothing about the GPS antenna cable length. When the WAAS update was released Garmin stated that the GPS antenna had to be at least 13 feet long. It also stated that it was alright to "coil" the antenna. I know of two RV 10s with G 430s, o e with the 13 foot antenna cable and one with a 3 foot (roughly) anrenna cable. There is no detectable difference in performance. I have not checked the current G430 WAAS manual for cable length requirements.

Don

On Mar 31, 2017 7:26 AM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote: 	  Quote: 	
		    At 06:01 AM 3/30/2017, you wrote:

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



 I am installing an Appareo Stratus ESG transponder with internal GPS.  It did not come with antenna cables.  I purchased a 19 inch RG400 GPS antenna cable before reading the installation directions which state, "All wiring should have a cable loss of minimum 2 dB . . . .Using RG400 the minimum cable length is 10 feet".

   Will the GPS work satisfactorily with the short cable?  If not, what is a cheap and easy way to increase the dB loss?  What is the theory behind the requirement for at least 2 dB cable loss? 	


   I'm having trouble wrapping my head around this

   requirement. GPS satellite signals are exceedingly

   tiny . . . down in the atmospheric noise levels.

   The only reason our tiny wrist-watch, hand-held,

   and self-navigating drones work so well is because

   the 'smarts' in GPS receiver software is looking for

   specific patterns of data in the chaotic patternless

   noise.



   Routine variations in received GPS signals

   is all over the magnitude map spanning perhaps

   tens of db . . . a required 2 db 'addition of 

   attenuation' simply doesn't make sense.



   The idea that a receiver's performance is

   predicated on a minimum of 2db of loss in the

   antenna system by making the cable longer is a

   real puzzle . . . usually, the instructions will

   say something like "limit cable losses to a MAXIMUM

   of 2db where a 10' run of RG-400 is the practical

   limit".



   I'm wondering if this manual wasn't originally crafted

   in Chinese and then translated by some academic instead

   of a systems engineer.



   One thing is for sure, if you install your system

   using only the needed length of coax, you can certainly

   ADD some later. I'm betting a dollar to a dozen doughnuts

   that it will not be necessary. 



 

 

   Bob . . .

donvansanten(at)gmail.com
Guest

Posted: Fri Mar 31, 2017 7:06 am Post subject: Minimum GPS Antenna Cable Length

My UPSAT 480 manual did mot list a cable length requirement. I used a 3 foot rg 400 csble and never had any issues with reception.



On Mar 31, 2017 08:00, "Tim Olson" <Tim(at)myrv10.com (Tim(at)myrv10.com)> wrote: 	  Quote: 	
		  

This is not that unusual. My Garman GNS480 had the same requirement.

Keep in mind that the antennas used are active antennas.

Tim



On Mar 31, 2017, at 9:16 AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

 	  Quote: 	
		    At 06:01 AM 3/30/2017, you wrote:

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



 I am installing an Appareo Stratus ESG transponder with internal GPS.  It did not come with antenna cables.  I purchased a 19 inch RG400 GPS antenna cable before reading the installation directions which state, "All wiring should have a cable loss of minimum 2 dB . . . .Using RG400 the minimum cable length is 10 feet".

   Will the GPS work satisfactorily with the short cable?  If not, what is a cheap and easy way to increase the dB loss?  What is the theory behind the requirement for at least 2 dB cable loss? 	


   I'm having trouble wrapping my head around this

   requirement. GPS satellite signals are exceedingly

   tiny . . . down in the atmospheric noise levels.

   The only reason our tiny wrist-watch, hand-held,

   and self-navigating drones work so well is because

   the 'smarts' in GPS receiver software is looking for

   specific patterns of data in the chaotic patternless

   noise.



   Routine variations in received GPS signals

   is all over the magnitude map spanning perhaps

   tens of db . . . a required 2 db 'addition of 

   attenuation' simply doesn't make sense.



   The idea that a receiver's performance is

   predicated on a minimum of 2db of loss in the

   antenna system by making the cable longer is a

   real puzzle . . . usually, the instructions will

   say something like "limit cable losses to a MAXIMUM

   of 2db where a 10' run of RG-400 is the practical

   limit".



   I'm wondering if this manual wasn't originally crafted

   in Chinese and then translated by some academic instead

   of a systems engineer.



   One thing is for sure, if you install your system

   using only the needed length of coax, you can certainly

   ADD some later. I'm betting a dollar to a dozen doughnuts

   that it will not be necessary. 



 

 

   Bob . . .

user9253

Joined: 28 Mar 2008
Posts: 1931
Location: Riley TWP Michigan

Posted: Fri Mar 31, 2017 7:27 am Post subject: Re: Minimum GPS Antenna Cable Length

It seems that the minimum cable length is a requirement of the GPS receiver and not of the antenna.  I agree with you Bob.  I always thought that shorter cable length is better.

I ordered 2 of 90 degree TNC adapters to increase the dB loss.  eBay item number: 232142074744

Below is a quote from a separate unrelated company.  Notice that they contradict themselves in the last sentence.

http://utahscientific.com/support/protected/fb_contemp/GPS%20Installation%20V1_6.pdf

 	  Quote: 	
		  In the world of GPS; too much signal gain can be just as detrimental as too little, and RF noise, even if it is out of band, can severely disrupt the performance of your GPS application. …

The Courtyard GPS receiver has a minimum input gain of 20dB and a maximum of 30dB.

The recommended antenna has a 26dB gain.

Recommended cable is RG58 and TNC connectors having a loss of 0.85dB per metre.

(RG174 has a loss of 1.2dB per meter.)

Maximum cable length is: (26dB-20dB)/0.85dBpermetre = 7.06 metres

Minimum cable length is: (30dB -26dB)/0.85dBpermetre = 4.70 meters

As a general rule, keep RF cable lengths as short as possible and use a good quality GPS antenna with the correct gain.

_________________
Joe Gores

stein(at)steinair.com
Guest

Posted: Fri Mar 31, 2017 7:36 am Post subject: Minimum GPS Antenna Cable Length

That is a fairly accurate statement correct.  For others who have 'used' or

'seen' shorter cables work, indeed sometimes they do...but I lost count of

the number of phone calls we've had from customers about antenna or GPS

issues, only to find out they had a short little cable.  Once extending the

cable to the proper length most issues disappeared.  Our recommendation is

to keep it on the longer side - sometimes shorter than 10' will be ok, but

something as short as 18" will almost certainly cause issues.



Cheers,

Stein

--

user9253

Joined: 28 Mar 2008
Posts: 1931
Location: Riley TWP Michigan

Posted: Fri Mar 31, 2017 7:57 am Post subject: Re: Minimum GPS Antenna Cable Length

Below is a quote from Garmin:

http://www.vansairforce.com/community/showpost.php?p=824265&postcount=3

 	  Quote: 	
		  Once the antenna mounting position has been prepared, route the coax cable from the antenna to the 400W Series unit. Proper selection of coax cable and assembly of connectors is critical to GPS signal performance. The cable loss from the GPS antenna shall be between 1.5 dB and 6.5 dB in order to aintain proper rejection to interference signals. 

The coaxial connectors and adapters, such as TNC to BNC, add additional loss to the cable and should be considered when computing the cable loss. A typical loss of 0.2 dB can be used for each connection.

NOTE: If RG-142B or RG-400 is used, 1.5 dB equates to a length of approximately 6.5 feet of cable with a connector on each end. RG-142B or RG-400 cable can be used as long as the length is less than 35 feet. 	


Another website says, "Be kind to the 0.000 000 000 000 000 1 watt GPS signal at the Antenna !!"

_________________
Joe Gores

ceengland7(at)gmail.com
Guest

Posted: Fri Mar 31, 2017 8:41 am Post subject: Minimum GPS Antenna Cable Length

I think we may be losing sight of what signal we're actually talking about.



It's extremely unlikely that the GPS antenna puck is sending raw, 

unamplified 1/5 GHZ RF to the receiver.



Most GPS pucks send either decoded digital data (serial or USB), or 

amplified 1.5GHZ RF, or amplified and downconverted IF (intermediate 

frequency) to the receiver. If it's either of the 2nd two options, then 

the next stage (in the receiver) can be overdriven by a very strong 

signal from the puck.



On 3/31/2017 10:57 AM, user9253 wrote:

 	  Quote: 	
		   



 Below is a quote from Garmin:

 http://www.vansairforce.com/community/showpost.php?p=824265&postcount=3



> Once the antenna mounting position has been prepared, route the coax cable from the antenna to the 400W Series unit. Proper selection of coax cable and assembly of connectors is critical to GPS signal performance. The cable loss from the GPS antenna shall be between 1.5 dB and 6.5 dB in order to aintain proper rejection to interference signals.

> The coaxial connectors and adapters, such as TNC to BNC, add additional loss to the cable and should be considered when computing the cable loss. A typical loss of 0.2 dB can be used for each connection.

> NOTE: If RG-142B or RG-400 is used, 1.5 dB equates to a length of approximately 6.5 feet of cable with a connector on each end. RG-142B or RG-400 cable can be used as long as the length is less than 35 feet.

 Another website says, "Be kind to the 0.000 000 000 000 000 1 watt GPS signal at the Antenna !!"



 --------

 Joe Gores

user9253

Joined: 28 Mar 2008
Posts: 1931
Location: Riley TWP Michigan

Posted: Fri Mar 31, 2017 1:11 pm Post subject: Re: Minimum GPS Antenna Cable Length

I will follow Stein's (and the Mfg's) recommendation and will use a 10 foot cable.  They are the experts.  It will be a lot easier to do it right the first time.

_________________
Joe Gores

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