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what is the truth about gps antennas?

 
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kjlpdx



Joined: 18 Dec 2018
Posts: 4

PostPosted: Wed Dec 19, 2018 7:23 pm    Post subject: what is the truth about gps antennas? Reply with quote

I'm interested in hearing from an engineer who might know about what really goes on with my stratus esg gps antenna. they say to use RG400 cable, 10' minimum, and never paint the antenna. they also told me the strength ratings should run in the 30's. I have 3' of RG400 with a mechanical 90° elbow, I spray painted the antenna flat black and mounted it on the glareshield of my RV. my readings are all in the 40's. they told me this shows an overdriven condition.
so why use low impedance cable then need 10'? my iFly740 and Lowrance 1000 gps's have antennas with much smaller cables. the iFly shows WAAS grade accuracy, using an antenna 1/4 the size of the stratus RAMI antenna.
when does being overdriven prove to be a problem? is this a situation where I could add more mechanical connectors to increase impedance rather than more cable length?
I get the feeling things get written and then forever repeated, such as never paint an antenna, without asking any questions. could I use a different antenna than the RAMI brand? should I not worry about any of this and just go fly?


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user9253



Joined: 28 Mar 2008
Posts: 1350
Location: Riley TWP Michigan

PostPosted: Thu Dec 20, 2018 7:00 am    Post subject: Re: what is the truth about gps antennas? Reply with quote

Read this thread:
http://forum.matronics.com/viewtopic.php?t=16766060&start=0&postdays=0&postorder=asc&highlight=&sid=4eec20ad70d380aa54524dd467494a91
While none of the postings were by GPS antenna engineers, their replies are based on experience. Stein owns an avionics company. He is the expert. Follow his recommendations.
If shorter cable must be used, consider RG-58.


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PostPosted: Thu Dec 20, 2018 8:56 am    Post subject: what is the truth about gps antennas? Reply with quote

At 09:23 PM 12/19/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "kjlpdx" <kevinlane55(at)gmail.com>

I'm interested in hearing from an engineer who might know about what really goes on with my stratus esg gps antenna. they say to use RG400 cable, 10' minimum, and never paint the antenna. they also told me the strength ratings should run in the 30's. I have 3' of RG400 with a mechanical 90° elbow, I spray painted the antenna flat black and mounted it on the glareshield of my RV. my readings are all in the 40's. they told me this shows an overdriven condition.
so why use low impedance cable then need 10'? my iFly740 and Lowrance 1000 gps's have antennas with much smaller cables. the iFly shows WAAS grade accuracy, using an antenna 1/4 the size of the stratus RAMI antenna.
when does being overdriven prove to be a problem? is this a situation where I could add more mechanical connectors to increase impedance rather than more cable length?
I get the feeling things get written and then forever repeated, such as never paint an antenna, without asking any questions. could I use a different antenna than the RAMI brand? should I not worry about any of this and just go fly?

Paint MIGHT degrade antenna performance
but without laboratory grade testing, you
don't know about YOUR paint. Hence, easiest
way to deal with it is never paint. Now,
if you have a painted antenna and the receiver
is still got good signal numbers, then
the 99% sure THAT paint is not an issue.

OVER-DRIVEN? Never heard of such a thing
in GPS receivers. RG400 has an attenuation
figure on the order of 16db typical to 20 db
maximum PER 100 FEET at GPS frequencies.
Assume worst at 20db/100' for a 10' feeder cable,
shortening it to ZERO feet would raise the
signal by 2db Maximum, probably less. This
is trivial.

Color be skeptical . . .

Antenna dimensions are only
loosely related to performance. Physical
and electrical things INSIDE make the
difference . . . and the technology
is now so old that manufacturing a good
antenna is child's play.

You certainly want to minimize connections
but don't loose any sleep over it if you've
added one for enhanced maintenance.

I've got a GPS cable on my bench signal generator
that is 20' long and RG174 style (relatively
high attenuation) that drives the GPS disciplined
reference oscillator . . . it gets stood up
in less than 2 minutes even after being off
for weeks.

There's been a lot of hangar-lore floating
around the aviation environs concerning
things technical for over a century. Sadly,
many 'field representatives' of major
suppliers are not all that cognizant of
foundations in physics for the products
they sell. Stories not backed up by
measurement and/or demonstration are
suspect. GPS is no exception.

If anyone encounters a 'factory representative'
who offers less than comfortable advice,
shoot me their name and phone number.

The proof of the pudding is in the flying.
You'll be getting error messages when an
if the receiver is being improperly serviced
by what's coming down the coax.


Bob . . .


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BARRY CHECK 6



Joined: 15 Mar 2011
Posts: 739

PostPosted: Sat Dec 22, 2018 4:48 pm    Post subject: what is the truth about gps antennas? Reply with quote

Hi Kevin:

 You are 300% right to question Old Wive's Tails.
The Paint Story is not without some merit. It stems from the idea of how the Color was produced.  Black and Gray for example could come from a CARBON.  Carbon is conductive, not highly so but conductive.  After all Carbon Resistors are exactly that Carbon and Conductive.
The old Green, Copper and Bronze have Copper and Bronze metals in them.
White paint can have Titanium Dioxide in it and titanium is metal and slightly conductive.
There are also paints such as primers which have Zinc in them.  
Well, you can see the thought process, that conductive paints can cause some problems.
So, why take the chance...  The industry makes a general Old Wive's Tail statement of Do Not Paint GPS Antennas.
Of course the Pigment of paints have changed over the years, too bad the Old Wive's Tails have a stronger following than the process of common sense. 
What YOU can do is read the Ingredients List of what makes the paint the color (Pigment) and see if any of the above items are listed.  ALSO, you can look up the MSDS for the paint.
Next: - 
OVER DRIVEN: - We should be so lucky.
YES!  There is such a thing.  It is also know in Receiver Theory as Front End Over Load.
Too much signal is received and causes SPLATTER - Too much signal covering too wide a bandwidth.
The 'Active" GPS  Antennas do  have amplifiers built into them.  They usually range between 10 to 40 dB Gain.
The rule of dB is every 3 dB doubles your signal. So, YES, in theory if you have a 40 dB gain antenna you could have 40/3 = 13 times the un-amplified signal.  That could be too much for the receiver to handle.
Of course there is a loss in the coax, loss in each of the connectors and an additional loss in the 90 Deg connector.
So, if an engineer sits down with the slide-ruler the NUMBERS would say YES, there is too much signal coming down the RG-400.  SO! Why not be smarter than the Engineer - Save your Money - Buy RG-58/AU and run the shortest length possible?  Buy It - HELL!  I have a 150 foot spool!  But NOooooo....   Common Sense is over ruled by Sales Pitch and owners spend $4.00 per foot for RG-400 and they buy 10 foot when only 3 foot is need for the run.  10 Foot (at) $4 = $40 Vs 3 Foot (at) $0.75 = $2.25.  
So Kevin,  you did VERY - VERY GOOD!
Guess What!  I did the EXACT same thing with the Stratus ESG coax situation as you.  I also mounted it on my Glare Shield.  But, I have a carper over the antenna so I did not have to paint the antenna.
Works Great, Works Fine - FM!
Barry


message posted by: "kjlpdx" <kevinlane55(at)gmail.com (kevinlane55(at)gmail.com)>
Quote:
Quote:

I'm interested in hearing from an engineer who might know about what really goes on with my stratus esg gps antenna. they say to use RG400 cable, 10' minimum, and never paint the antenna. they also told me the strength ratings should run in the 30's. I have 3' of RG400 with a mechanical 90° elbow, I spray painted the antenna flat black and mounted it on the glareshield of my RV. my readings are all in the 40's. they told me this shows an overdriven condition.
so why use low impedance cable then need 10'? my iFly740 and Lowrance 1000 gps's have antennas with much smaller cables. the iFly shows WAAS grade accuracy, using an antenna 1/4 the size of the stratus RAMI antenna.
when does being overdriven prove to be a problem? is this a situation where I could add more mechanical connectors to increase impedance rather than more cable length?
I get the feeling things get written and then forever repeated, such as never paint an antenna, without asking any questions. could I use a different antenna than the RAMI brand? should I not worry about any of this and just go fly?



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PostPosted: Sat Dec 22, 2018 6:11 pm    Post subject: what is the truth about gps antennas? Reply with quote

It's an old wive's tale that a 40 dB gain is 40/3 = 13 times power gain over 0 dB.
The decibel is a ratio of two physical properties expressed mathematically using logarithmic base 10. When referring to power, below are the calculated values using the equation dB = 10xLog10(P/Po):
0 dB = 1
3 dB = 1.995 = ~2
6 dB = 3.981 = ~4
9 dB = 7.95 = ~8
10 dB = 10.0
20 dB = 100.0
30 dB = 1000.0
40 dB = 10,000.0

So 40 DB represents a ratio of 10,000, not 13. If 0 dB = 1 milliWatt, then 40 dB = 10 Watts.
Everything else you say below is correct except that RF engineers, as well as LiDAR engineers, refer to too much signal as saturation, not splatter. Maybe I'm hanging out with a different bunch of engineers, but we use what the literature says.

Henador Titzoff




On Saturday, December 22, 2018, 8:03:24 PM EST, FLYaDIVE <flyadive(at)gmail.com> wrote:




Hi Kevin:

You are 300% right to question Old Wive's Tails.
The Paint Story is not without some merit. It stems from the idea of how the Color was produced. Black and Gray for example could come from a CARBON. Carbon is conductive, not highly so but conductive. After all Carbon Resistors are exactly that Carbon and Conductive.
The old Green, Copper and Bronze have Copper and Bronze metals in them.
White paint can have Titanium Dioxide in it and titanium is metal and slightly conductive.
There are also paints such as primers which have Zinc in them.
Well, you can see the thought process, that conductive paints can cause some problems.
So, why take the chance... The industry makes a general Old Wive's Tail statement of Do Not Paint GPS Antennas.
Of course the Pigment of paints have changed over the years, too bad the Old Wive's Tails have a stronger following than the process of common sense.
What YOU can do is read the Ingredients List of what makes the paint the color (Pigment) and see if any of the above items are listed. ALSO, you can look up the MSDS for the paint.
Next: -
OVER DRIVEN: - We should be so lucky.
YES! There is such a thing. It is also know in Receiver Theoryas Front End Over Load.
Too much signal is received and causes SPLATTER- Too much signal covering too wide a bandwidth.
The 'Active" GPS Antennas do have amplifiers built into them. They usually range between 10 to 40 dB Gain.
The rule of dB is every 3 dB doubles your signal. So, YES, in theory if you have a 40 dB gain antenna you could have 40/3 = 13 times the un-amplified signal. That could be too much for the receiver to handle.
Of course there is a loss in the coax, loss in each of the connectors and an additional loss in the 90 Deg connector.
So, if an engineer sits down with the slide-ruler the NUMBERS would say YES, there is too much signal coming down the RG-400. SO! Why not be smarter than the Engineer - Save your Money - Buy RG-58/AU and run the shortest length possible? Buy It - HELL! I have a 150 foot spool! But NOooooo.... Common Sense is over ruled by Sales Pitch and owners spend $4.00 per foot for RG-400 and they buy 10 foot when only 3 foot is need for the run. 10 Foot (at) $4 = $40 Vs 3 Foot (at) $0.75 = $2.25.
So Kevin, you did VERY - VERY GOOD!
Guess What! I did the EXACT same thing with the Stratus ESG coax situation as you. I also mounted it on my Glare Shield. But, I have a carper over the antenna so I did not have to paint the antenna.
Works Great, Works Fine - FM!
Barry


message posted by: "kjlpdx" <kevinlane55(at)gmail.com (kevinlane55(at)gmail.com)>
Quote:
Quote:

I'm interested in hearing from an engineer who might know about what really goes on with my stratus esg gps antenna. they say to use RG400 cable, 10' minimum, and never paint the antenna. they also told me the strength ratings should run in the 30's. I have 3' of RG400 with a mechanical 90° elbow, I spray painted the antenna flat black and mounted it on the glareshield of my RV. my readings are all in the 40's. they told me this shows an overdriven condition.
so why use low impedance cable then need 10'? my iFly740 and Lowrance 1000 gps's have antennas with much smaller cables. the iFly shows WAAS grade accuracy, using an antenna 1/4 the size of the stratus RAMI antenna.
when does being overdriven prove to be a problem? is this a situation where I could add more mechanical connectors to increase impedance rather than more cable length?
I get the feeling things get written and then forever repeated, such as never paint an antenna, without asking any questions. could I use a different antenna than the RAMI brand? should I not worry about any of this and just go fly?



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PostPosted: Sat Dec 22, 2018 8:27 pm    Post subject: what is the truth about gps antennas? Reply with quote

40dB is 40/3 = 13.3 doublings, or a ratio of 2^13.3, which is about 10,000, as you say.

On Dec 22, 2018, at 21:10, Henador Titzoff <henador_titzoff(at)yahoo.com (henador_titzoff(at)yahoo.com)> wrote:
It's an old wive's tale that a 40 dB gain is 40/3 = 13 times power gain over 0 dB.
The decibel is a ratio of two physical properties expressed mathematically using logarithmic base 10. When referring to power, below are the calculated values using the equation dB = 10xLog10(P/Po):
0 dB = 1
3 dB = 1.995 = ~2
6 dB = 3.981 = ~4
9 dB = 7.95 = ~8
10 dB = 10.0
20 dB = 100.0
30 dB = 1000.0
40 dB = 10,000.0

So 40 DB represents a ratio of 10,000, not 13. If 0 dB = 1 milliWatt, then 40 dB = 10 Watts.
Everything else you say below is correct except that RF engineers, as well as LiDAR engineers, refer to too much signal as saturation, not splatter. Maybe I'm hanging out with a different bunch of engineers, but we use what the literature says.

Henador Titzoff




On Saturday, December 22, 2018, 8:03:24 PM EST, FLYaDIVE <flyadive(at)gmail.com (flyadive(at)gmail.com)> wrote:




Hi Kevin:

You are 300% right to question Old Wive's Tails.
The Paint Story is not without some merit. It stems from the idea of how the Color was produced. Black and Gray for example could come from a CARBON. Carbon is conductive, not highly so but conductive. After all Carbon Resistors are exactly that Carbon and Conductive.
The old Green, Copper and Bronze have Copper and Bronze metals in them.
White paint can have Titanium Dioxide in it and titanium is metal and slightly conductive.
There are also paints such as primers which have Zinc in them.
Well, you can see the thought process, that conductive paints can cause some problems.
So, why take the chance... The industry makes a general Old Wive's Tail statement of Do Not Paint GPS Antennas.
Of course the Pigment of paints have changed over the years, too bad the Old Wive's Tails have a stronger following than the process of common sense.
What YOU can do is read the Ingredients List of what makes the paint the color (Pigment) and see if any of the above items are listed. ALSO, you can look up the MSDS for the paint.
Next: -
OVER DRIVEN: - We should be so lucky.
YES! There is such a thing. It is also know in Receiver Theory as Front End Over Load.
Too much signal is received and causes SPLATTER - Too much signal covering too wide a bandwidth.
The 'Active" GPS Antennas do have amplifiers built into them. They usually range between 10 to 40 dB Gain.
The rule of dB is every 3 dB doubles your signal. So, YES, in theory if you have a 40 dB gain antenna you could have 40/3 = 13 times the un-amplified signal. That could be too much for the receiver to handle.
Of course there is a loss in the coax, loss in each of the connectors and an additional loss in the 90 Deg connector.
So, if an engineer sits down with the slide-ruler the NUMBERS would say YES, there is too much signal coming down the RG-400. SO! Why not be smarter than the Engineer - Save your Money - Buy RG-58/AU and run the shortest length possible? Buy It - HELL! I have a 150 foot spool! But NOooooo.... Common Sense is over ruled by Sales Pitch and owners spend $4.00 per foot for RG-400 and they buy 10 foot when only 3 foot is need for the run. 10 Foot (at) $4 = $40 Vs 3 Foot (at) $0.75 = $2.25.
So Kevin, you did VERY - VERY GOOD!
Guess What! I did the EXACT same thing with the Stratus ESG coax situation as you. I also mounted it on my Glare Shield. But, I have a carper over the antenna so I did not have to paint the antenna.
Works Great, Works Fine - FM!
Barry


message posted by: "kjlpdx" <kevinlane55(at)gmail.com (kevinlane55(at)gmail.com)>
Quote:
Quote:

I'm interested in hearing from an engineer who might know about what really goes on with my stratus esg gps antenna. they say to use RG400 cable, 10' minimum, and never paint the antenna. they also told me the strength ratings should run in the 30's. I have 3' of RG400 with a mechanical 90° elbow, I spray painted the antenna flat black and mounted it on the glareshield of my RV. my readings are all in the 40's. they told me this shows an overdriven condition.
so why use low impedance cable then need 10'? my iFly740 and Lowrance 1000 gps's have antennas with much smaller cables. the iFly shows WAAS grade accuracy, using an antenna 1/4 the size of the stratus RAMI antenna.
when does being overdriven prove to be a problem? is this a situation where I could add more mechanical connectors to increase impedance rather than more cable length?
I get the feeling things get written and then forever repeated, such as never paint an antenna, without asking any questions. could I use a different antenna than the RAMI brand? should I not worry about any of this and just go fly?



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BARRY CHECK 6



Joined: 15 Mar 2011
Posts: 739

PostPosted: Sun Dec 23, 2018 6:13 am    Post subject: what is the truth about gps antennas? Reply with quote

Alec:
I did say "Rule of Thumb".  I did not look up if the dB gain expressed in the manual is voltage or power, but I'm pretty sure it would be voltage.  And the rule of thumb is the voltage signal will double with every 3 dB of gain.  Ya got me...  I did not sit down with my slide rule and work out the voltage gain, I am  just trying to show a relative number that non engineers can work with.  
But, your numbers are incorrect.  A 10,000:1 dB ratio gain would be more like 80 dB's not 40 dB's.
See: Common Gains and Losses Expressed in Decibels


http://www.sengpielaudio.com/calculator-FactorRatioLevelDecibel.htm

Barry



On Sat, Dec 22, 2018 at 11:31 PM Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)> wrote:

Quote:

40dB is 40/3 = 13.3 doublings, or a ratio of 2^13.3, which is about 10,000, as you say.

On Dec 22, 2018, at 21:10, Henador Titzoff <henador_titzoff(at)yahoo.com (henador_titzoff(at)yahoo.com)> wrote:
It's an old wive's tale that a 40 dB gain is 40/3 = 13 times power gain over 0 dB.
The decibel is a ratio of two physical properties expressed mathematically using logarithmic base 10.  When referring to power, below are the calculated values using the equation dB = 10xLog10(P/Po):
    0 dB = 1
    3 dB = 1.995 = ~2
    6 dB = 3.981 = ~4
    9 dB = 7.95  = ~8
  10 dB = 10.0
  20 dB = 100.0
  30 dB = 1000.0
  40 dB = 10,000.0

So 40 DB represents a ratio of 10,000, not 13.  If 0 dB = 1 milliWatt, then 40 dB = 10 Watts.
Everything else you say below is correct except that RF engineers, as well as LiDAR engineers, refer to too much signal as saturation, not splatter.  Maybe I'm hanging out with a different bunch of engineers, but we use what the literature says.

Henador Titzoff




On Saturday, December 22, 2018, 8:03:24 PM EST, FLYaDIVE <flyadive(at)gmail.com (flyadive(at)gmail.com)> wrote:




Hi Kevin:

 You are 300% right to question Old Wive's Tails.
The Paint Story is not without some merit. It stems from the idea of how the Color was produced.  Black and Gray for example could come from a CARBON.  Carbon is conductive, not highly so but conductive.  After all Carbon Resistors are exactly that Carbon and Conductive.
The old Green, Copper and Bronze have Copper and Bronze metals in them.
White paint can have Titanium Dioxide in it and titanium is metal and slightly conductive.
There are also paints such as primers which have Zinc in them.  
Well, you can see the thought process, that conductive paints can cause some problems.
So, why take the chance...  The industry makes a general Old Wive's Tail statement of Do Not Paint GPS Antennas.
Of course the Pigment of paints have changed over the years, too bad the Old Wive's Tails have a stronger following than the process of common sense. 
What YOU can do is read the Ingredients List of what makes the paint the color (Pigment) and see if any of the above items are listed.  ALSO, you can look up the MSDS for the paint.
Next: - 
OVER DRIVEN: - We should be so lucky.
YES!  There is such a thing.  It is also know in Receiver Theory as Front End Over Load.
Too much signal is received and causes SPLATTER - Too much signal covering too wide a bandwidth.
The 'Active" GPS  Antennas do  have amplifiers built into them.  They usually range between 10 to 40 dB Gain.
The rule of dB is every 3 dB doubles your signal. So, YES, in theory if you have a 40 dB gain antenna you could have 40/3 = 13 times the un-amplified signal.  That could be too much for the receiver to handle.
Of course there is a loss in the coax, loss in each of the connectors and an additional loss in the 90 Deg connector.
So, if an engineer sits down with the slide-ruler the NUMBERS would say YES, there is too much signal coming down the RG-400.  SO! Why not be smarter than the Engineer - Save your Money - Buy RG-58/AU and run the shortest length possible?  Buy It - HELL!  I have a 150 foot spool!  But NOooooo....   Common Sense is over ruled by Sales Pitch and owners spend $4.00 per foot for RG-400 and they buy 10 foot when only 3 foot is need for the run.  10 Foot (at) $4 = $40 Vs 3 Foot (at) $0.75 = $2.25.  
So Kevin,  you did VERY - VERY GOOD!
Guess What!  I did the EXACT same thing with the Stratus ESG coax situation as you.  I also mounted it on my Glare Shield.  But, I have a carper over the antenna so I did not have to paint the antenna.
Works Great, Works Fine - FM!
Barry


message posted by: "kjlpdx" <kevinlane55(at)gmail.com (kevinlane55(at)gmail.com)>
Quote:
Quote:

I'm interested in hearing from an engineer who might know about what really goes on with my stratus esg gps antenna. they say to use RG400 cable, 10' minimum, and never paint the antenna. they also told me the strength ratings should run in the 30's. I have 3' of RG400 with a mechanical 90° elbow, I spray painted the antenna flat black and mounted it on the glareshield of my RV. my readings are all in the 40's. they told me this shows an overdriven condition.
so why use low impedance cable then need 10'? my iFly740 and Lowrance 1000 gps's have antennas with much smaller cables. the iFly shows WAAS grade accuracy, using an antenna 1/4 the size of the stratus RAMI antenna.
when does being overdriven prove to be a problem? is this a situation where I could add more mechanical connectors to increase impedance rather than more cable length?
I get the feeling things get written and then forever repeated, such as never paint an antenna, without asking any questions. could I use a different antenna than the RAMI brand? should I not worry about any of this and just go fly?







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PostPosted: Sun Dec 23, 2018 6:33 am    Post subject: what is the truth about gps antennas? Reply with quote

3dB is a doubling of whatever you measure. (Actually a factor of 10^0.3 = 1.995)
Of course you have to say what you’re comparing with, so we talk about dBA, dBV, dBm, for sound level relative to the quietest detectable by the human ear, volts, or power (in mW), respectively.
If you’re talking about Voltage then 40dB is by definition a ratio of 10,000 to 1. Which, into the same load impedance corresponds to a power ratio of 10^8 to 1.

On Dec 23, 2018, at 09:04, FLYaDIVE <flyadive(at)gmail.com (flyadive(at)gmail.com)> wrote:
Alec:
I did say "Rule of Thumb". I did not look up if the dB gain expressed in the manual is voltage or power, but I'm pretty sure it would be voltage. And the rule of thumb is the voltage signal will double with every 3 dB of gain. Ya got me... I did not sit down with my slide rule and work out the voltage gain, I am just trying to show a relative number that non engineers can work with.
But, your numbers are incorrect. A 10,000:1 dB ratio gain would be more like 80 dB's not 40 dB's.
See: Common Gains and Losses Expressed in Decibels


http://www.sengpielaudio.com/calculator-FactorRatioLevelDecibel.htm

Barry



On Sat, Dec 22, 2018 at 11:31 PM Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)> wrote:

Quote:

40dB is 40/3 = 13.3 doublings, or a ratio of 2^13.3, which is about 10,000, as you say.

On Dec 22, 2018, at 21:10, Henador Titzoff <henador_titzoff(at)yahoo.com (henador_titzoff(at)yahoo.com)> wrote:
It's an old wive's tale that a 40 dB gain is 40/3 = 13 times power gain over 0 dB.
The decibel is a ratio of two physical properties expressed mathematically using logarithmic base 10. When referring to power, below are the calculated values using the equation dB = 10xLog10(P/Po):
0 dB = 1
3 dB = 1.995 = ~2
6 dB = 3.981 = ~4
9 dB = 7.95 = ~8
10 dB = 10.0
20 dB = 100.0
30 dB = 1000.0
40 dB = 10,000.0

So 40 DB represents a ratio of 10,000, not 13. If 0 dB = 1 milliWatt, then 40 dB = 10 Watts.
Everything else you say below is correct except that RF engineers, as well as LiDAR engineers, refer to too much signal as saturation, not splatter. Maybe I'm hanging out with a different bunch of engineers, but we use what the literature says.

Henador Titzoff




On Saturday, December 22, 2018, 8:03:24 PM EST, FLYaDIVE <flyadive(at)gmail.com (flyadive(at)gmail.com)> wrote:




Hi Kevin:

You are 300% right to question Old Wive's Tails.
The Paint Story is not without some merit. It stems from the idea of how the Color was produced. Black and Gray for example could come from a CARBON. Carbon is conductive, not highly so but conductive. After all Carbon Resistors are exactly that Carbon and Conductive.
The old Green, Copper and Bronze have Copper and Bronze metals in them.
White paint can have Titanium Dioxide in it and titanium is metal and slightly conductive.
There are also paints such as primers which have Zinc in them.
Well, you can see the thought process, that conductive paints can cause some problems.
So, why take the chance... The industry makes a general Old Wive's Tail statement of Do Not Paint GPS Antennas.
Of course the Pigment of paints have changed over the years, too bad the Old Wive's Tails have a stronger following than the process of common sense.
What YOU can do is read the Ingredients List of what makes the paint the color (Pigment) and see if any of the above items are listed. ALSO, you can look up the MSDS for the paint.
Next: -
OVER DRIVEN: - We should be so lucky.
YES! There is such a thing. It is also know in Receiver Theory as Front End Over Load.
Too much signal is received and causes SPLATTER - Too much signal covering too wide a bandwidth.
The 'Active" GPS Antennas do have amplifiers built into them. They usually range between 10 to 40 dB Gain.
The rule of dB is every 3 dB doubles your signal. So, YES, in theory if you have a 40 dB gain antenna you could have 40/3 = 13 times the un-amplifiedsignal. That could be too much for the receiver to handle.
Of course there is a loss in the coax, loss in each of the connectors and an additional loss in the 90 Deg connector.
So, if an engineer sits down with the slide-ruler the NUMBERS would say YES, there is too much signal coming down the RG-400. SO! Why not be smarter than the Engineer - Save your Money - Buy RG-58/AU and run the shortest length possible? Buy It - HELL! I have a 150 foot spool! But NOooooo... Common Sense is over ruled by Sales Pitch and owners spend $4.00 per foot for RG-400 and they buy 10 foot when only 3 foot is need for the run. 10 Foot (at) $4 = $40 Vs 3 Foot (at) $0.75 = $2.25.
So Kevin, you did VERY - VERY GOOD!
Guess What! I did the EXACT same thing with the Stratus ESG coax situation as you. I also mounted it on my Glare Shield. But, I have a carper over the antenna so I d3167144365348388273gmail-m_3439025865685676282ydp424ffda5yiv8328154622gmail_default">

Works Great, Works Fine - FM!
Barry


message posted by: "kjlpdx" <kevinlane55(at)gmail.com (kevinlane55(at)gmail.com)>
Quote:
Quote:

I'm interested in hearing from an engineer who might know about what really goes on with my stratus esg gps antenna. they say to use RG400 cable, 10' minimum, and never paint the antenna. they also told me the strength ratings should run in the 30's. I have 3' of RG400 with a mechanical 90° elbow, I spray painted the antenna flat black and mounted it on the glareshield of my RV. my readings are all in the 40's. they told me this shows an overdriven condition.
so why use low impedance cable then need 10'? my iFly740 and Lowrance 1000 gps's have antennas with much smaller cables. the iFly shows WAAS grade accuracy, using an antenna 1/4 the size of the stratus RAMI antenna.
when does being overdriven prove to be a problem? is this a situation where I could add more mechanical connectors to increase impedance rather than more cable length?
I get the feeling things get written and then forever repeated, such as never paint an antenna, without asking any questions. could I use a different antenna than the RAMI brand? should I not worry about any of this and just go fly?







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PostPosted: Sun Dec 23, 2018 7:34 am    Post subject: what is the truth about gps antennas? Reply with quote

Quote:
3dB is a doubling of whatever you measure. (Actually a factor of 10^0.3 = 1.995)

I see this is actually true only for power quantities and power-like quantities. For field quantities and field-like quantities 3dB is a ratio of 10^0.15 = 1.41. So a signal ratio of 40dB is ten thousand times the power and 100 times the voltage.

That’s what you get when you put the engineers in charge of defining units instead of the physicists...


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Joined: 15 Mar 2011
Posts: 739

PostPosted: Sun Dec 23, 2018 8:14 am    Post subject: what is the truth about gps antennas? Reply with quote

Quote:
That’s what you get when you put the engineers in charge of defining units instead of the physicists...


I TOTALLY AGREE!  
I  have NEVER seen a more argumentative bunch than Engineers.
They all went  to collage.
They all took the same courses.
They all learned the SAME physics.  <-- Well,they should have!
They all learned the same electronics.
Yet they disagree on more things than Congress.
Three Engineers, an Electrical Engineer, a Mechanical Engineer and a Civil Engineer were discussing what kind of an engineer GOD must be.

The Electrical Engineer said: He must be an Electrical Engineer, think about it:
And consider the miles of nerve courses in the body.  Consider all the nerve endings.  Consider all the synapse’s in the brain sending electrical impulses all throughout the body.  GOD is an Electrical Engineer!
 
The Mechanical Engineer spoke up and said:  He must be a Mechanical Engineer, think about it:
And consider all of the bones throughout the body.  Consider all the muscles pulling against each other supporting the bones.  Consider how all the bones and muscles can reproduce as they become weak or damaged.  GOD is a Mechanical Engineer!
 
Then the Civil Engineer spoke up and said:  He MUST be a Civil Engineer – And with that the other two engineers broke into a raucous laughter.  Again the Civil Engineer spoke up and said:  Think about it:
Who else other than a Civil Engineer would put a waste dump right around the corner from a playground?
 
Barry


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PostPosted: Sun Dec 23, 2018 8:57 am    Post subject: what is the truth about gps antennas? Reply with quote

There was a fourth person in the story, a politician, who went last. He said, “God was most certainly a politician. The Bible says in the beginning there was chaos.  Who do you think created the chaos?”

Lyn

On Sun, Dec 23, 2018 at 08:18 FLYaDIVE <flyadive(at)gmail.com (flyadive(at)gmail.com)> wrote:

Quote:
Quote:
That’s what you get when you put the engineers in charge of defining units instead of the physicists...


I TOTALLY AGREE!  
I  have NEVER seen a more argumentative bunch than Engineers.
They all went  to collage.
They all took the same courses.
They all learned the SAME physics.  <-- Well,they should have!
They all learned the same electronics.
Yet they disagree on more things than Congress.
Three Engineers, an Electrical Engineer, a Mechanical Engineer and a Civil Engineer were discussing what kind of an engineer GOD must be.

The Electrical Engineer said: He must be an Electrical Engineer, think about it:
And consider the miles of nerve courses in the body.  Consider all the nerve endings.  Consider all the synapse’s in the brain sending electrical impulses all throughout the body.  GOD is an Electrical Engineer!
 
The Mechanical Engineer spoke up and said:  He must be a Mechanical Engineer, think about it:
And consider all of the bones throughout the body.  Consider all the muscles pulling against each other supporting the bones.  Consider how all the bones and muscles can reproduce as they become weak or damaged.  GOD is a Mechanical Engineer!
 
Then the Civil Engineer spoke up and said:  He MUST be a Civil Engineer – And with that the other two engineers broke into a raucous laughter.  Again the Civil Engineer spoke up and said:  Think about it:
Who else other than a Civil Engineer would put a waste dump right around the corner from a playground?
 
Barry


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Joined: 15 Mar 2011
Posts: 739

PostPosted: Sun Dec 23, 2018 10:01 am    Post subject: what is the truth about gps antennas? Reply with quote

On Sun, Dec 23, 2018 at 12:01 PM Lyn Robertson <lyn.robertson(at)gmail.com (lyn.robertson(at)gmail.com)> wrote:

Quote:
There was a fourth person in the story, a politician, who went last. He said, “God was most certainly a politician. The Bible says in the beginning there was chaos.  Who do you think created the chaos?”

Lyn


But Politicians are not Engineers.  For if they were, an engineer, they would have invented a better way to cover their ass, other than by rhetoric and at the people's expense.
Barry


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PostPosted: Sun Dec 23, 2018 11:44 am    Post subject: what is the truth about gps antennas? Reply with quote

While we’re on the subject….

A mathematician, a physicist and an engineer are all asked to examine the hypothesis that all odd numbers are prime.

The mathematician goes first, saying as follows:
“One is prime, three is prime, five is prime, seven is prime, nine ISN’T prime, so the hypothesis fails by counterexample”.

Then the physicist, who says:
“One is prime, three is prime, five is prime, seven is prime, nine isn’t prime, but we’ll call it experimental error, eleven is prime and thirteen is prime. That’s enough for me. I accept the hypothesis as true.

Finally the engineer steps up.
“One is prime, three is prime, five is prime, seven is prime, nine is prime….”


And here’s one for the maths nerds amongst us:

Q: What’s green and commutes?
A: An Abeilan grape.

On Dec 23, 2018, at 1:00 PM, FLYaDIVE <flyadive(at)gmail.com> wrote:

On Sun, Dec 23, 2018 at 12:01 PM Lyn Robertson <lyn.robertson(at)gmail.com> wrote:
There was a fourth person in the story, a politician, who went last. He said, “God was most certainly a politician. The Bible says in the beginning there was chaos. Who do you think created the chaos?”

Lyn

But Politicians are not Engineers. For if they were, an engineer, they would have invented a better way to cover their ass, other than by rhetoric and at the people's expense.

Barry


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PostPosted: Sun Dec 23, 2018 7:48 pm    Post subject: what is the truth about gps antennas? Reply with quote

You have a better way to cover your rear than at other people's expense?


On Sunday, December 23, 2018, 1:02:34 PM EST, FLYaDIVE <flyadive(at)gmail.com> wrote:






On Sun, Dec 23, 2018 at 12:01 PM Lyn Robertson <lyn.robertson(at)gmail.com (lyn.robertson(at)gmail.com)> wrote:

Quote:
There was a fourth person in the story, a politician, who went last. He said, “God was most certainly a politician. The Bible says in the beginning there was chaos. Who do you think created the chaos?”

Lyn


But Politicians are not Engineers. For if they were, an engineer, they would have invented a better way to cover their ass, other than by rhetoric and at the people's expense.
Barry


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Joined: 15 Mar 2011
Posts: 739

PostPosted: Sun Dec 23, 2018 8:19 pm    Post subject: what is the truth about gps antennas? Reply with quote

Ernest:
You are 100% correct.  Sad but true, why do what's right when you can do what you want and put the blame on someone else.  Why dip into your own pocket when you can steal from someone else.  AND steal legally!
Barry
On Sun, Dec 23, 2018 at 10:53 PM Ernest Christley <echristley(at)att.net (echristley(at)att.net)> wrote:

Quote:

You have a better way to cover your rear than at other people's expense?


On Sunday, December 23, 2018, 1:02:34 PM EST, FLYaDIVE <flyadive(at)gmail.com (flyadive(at)gmail.com)> wrote:






On Sun, Dec 23, 2018 at 12:01 PM Lyn Robertson <lyn.robertson(at)gmail.com (lyn.robertson(at)gmail.com)> wrote:

Quote:
There was a fourth person in the story, a politician, who went last. He said, “God was most certainly a politician. The Bible says in the beginning there was chaos.  Who do you think created the chaos?”

Lyn


But Politicians are not Engineers.  For if they were, an engineer, they would have invented a better way to cover their ass, other than by rhetoric and at the people's expense.
Barry





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PostPosted: Mon Dec 24, 2018 5:02 am    Post subject: what is the truth about gps antennas? Reply with quote

At 09:33 AM 12/23/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com>



>3dB is a doubling of whatever you measure. (Actually a factor of 10^0.3 = 1.995)

I see this is actually true only for power quantities and power-like quantities. For field quantities and field-like quantities 3dB is a ratio of 10^0.15 = 1.41. So a signal ratio of 40dB is ten thousand times the power and 100 times the voltage.

That’s what you get when you put the engineers in charge of defining units instead of the physicists.

The Bel (or its smaller descendant deciBel) was
derived from concepts in physics. . . as were
many other dimensionless numbers that described
RATIOS of many quantities that do have dimensions.
Look up dimensionless physical constants like
proton to electron mass ratio, Plank's constant,
Coulomb's constant, etc.

Then there are ratios near and dear to aviation
like Mach number, Reynolds number, strain,
and yes . . . even deciBels. The Bel is
always about energy ratios but is still
valid for discussion power. While power
is a rate function, it is proportional to energy
when the rates are defined over the same intervals
of time.

It is proper to discuss ratios of power (like
watts) and amplitudes (like voltage, amps) in
terms of dB if one compensates for the effects of
amplitude on power in the system. This is
accomplished with application of formula
that accounts for the square law effects
of amplitude on power. Hence the constant
for "deci" (10) has to be doubled to 20
when considering ratios of amplitude.

[img]cid:.0[/img]
This was no shortcoming on the part of
engineers vs. physicists . . . they've
all been on the same page since day-one.



Bob . . .


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PostPosted: Mon Dec 24, 2018 5:05 am    Post subject: what is the truth about gps antennas? Reply with quote

At 10:13 AM 12/23/2018, you wrote:
Quote:
That’s what you get when you put the engineers in charge of defining units instead of the physicists...


I TOTALLY AGREE!

I have NEVER seen a more argumentative bunch than Engineers.
They all went to collage.
They all took the same courses.
They all learned the SAME physics. <-- Well,they should have!
They all learned the same electronics.
Yet they disagree on more things than Congress.

I cannot speak for your personal experiences
except to observed that they are far removed
from my own. But in any case, this line
of thought does not advance the mission
of this forum.



Bob . . .


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