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Ground plane diameter

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n744bh(at)bellsouth.net
Guest

Posted: Mon Feb 25, 2013 1:33 pm Post subject: Ground plane diameter

I'm upgrading avionics in my Glasair and one of the units I'm  adding is a Garmin GDL-88 for ADS-B out.  The antenna I'm using is a Comant  CI-105 and seeing it's a "plastic" airplane I've been wondering if a 6" diameter  copper disc is large enough for the ground plane or should I go a bit  larger?  TIA

  

 Bill

 Glasair SIIS-FT



No virus found in this message.

 Checked by AVG - www.avg.com

 p>     [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Feb 25, 2013 6:00 pm Post subject: Ground plane diameter

At 03:30 PM 2/25/2013, you wrote:

  	  Quote: 	
		  I'm upgrading avionics in my Glasair and one of the units I'm adding is a Garmin GDL-88 for ADS-B out.  The antenna I'm using is a Comant CI-105 and seeing it's a "plastic" airplane I've been wondering if a 6" diameter copper disc is large enough for the ground plane or should I go a bit larger?  TIA 	




    To understand the workings of ground planes under

    vertical 1/4-wave radiators (like comm, transponder

    and DME) antennas, you need to take a little 'head

    trip'.



    The older brother to a 1/4-wave antenna fed at the

    base is a 1/2-wave antenna fed at the center (aka

    VOR/LOC/GS atennas). The 1/2 wave antenna doesn't

    need a 'ground' because is has useful places to send

    1/2 of the total energy into each of two identical,

    complimentary radiators.



    Now, take a dipole and turn it up vertically as if

    you wanted to use it for comm. Hmmmm . . . hard to

    attach the coax to it while insulating the hot

    end of the lower element. Okay, bend the lower element

    90 degrees. Now the feed point at the antenna

    center comes down to skin level on the airplane . . .

    but the 'bent' half of the antenna is seriously

    compromised for efficiency as it no longer works

    in concert with its unmodified counterpart.



    Hmmmm . . . how to make the lion's share of the energy

    flow into the freely extended portion of the antenna

    while reducing a wasteful venture onto the

    compromised portion of the antenna? How about adding

    a second compromised element? Assume the feed point

    impedance of each element is R. Then a dipole in

    extended splendor has a feed point impedance of 2R.



    You've still got R + R with the compromised dipole

    but paralleling two 'crippled' elements at the base

    gives you 1/2R + R. We see that energy fed to

    this network divides with 1/3 going to the compromised

    side and 2/3 to the free element. Let's consider adding

    2 more 'compromised' elements. Now we have 1/4R + R.

    Great! 4/5ths of the energy goes to the working part

    while only 1/5th is left free to roam and be a general

    nuisance to your radiation pattern.



    Now, if you want to squirt your signal off at an

    angle that is closer to the horizon, you can droop

    those elements not unlike the antennas seen around

    many airports.



 

   



    Take this exercise to an extreme . . . say 100

    'compromised' elements. Now you get 1/100R + R

    and only 1% of the energy is left free to be

    problematic. Further, 100 compromised elements

    look very close to a solid disk of material having

    a RADIUS equal to the HEIGHT of the free element.

    You sometimes see 100 drooping elements that look

    very much like a cone of solid metal.



    So, getting back to your question, the IDEAL small

    ground plane has a radius equal to the 1/4-wave

    distance for the frequency of interest. In the case

    of transponders, this works out to 300M meters/sec

    divided by 1050 cycles/second times 39.36 inches/meter

    times 0.25 wavelength and you get 2.8 inches. Twice

    this value is 5.6", the ideal resonant ground plane

    for transponder antennas.



    Making it just a little bigger because you can is

    counter productive. On the other hand, making it

    MUCH bigger (like the belly of a metal airplane)

    and it begins to approximate a non-resonant, infinite

    ground plane which is very good too . . . but a

    a whole different ballgame.



    The short answer is that for a non-conducting

    mounting surface the antenna performs best with

    the idealized, 1/4-wave radius disk. If you

    could mount it to several square feet of aluminum

    it would only slightly better . . . so slight

    that you would need to measure the difference

    in a well heeled RF lab. So the best recommendation

    is go for the 5.6" disk.



 

   Bob . . .    [quote][b]

n744bh(at)bellsouth.net
Guest

Posted: Mon Feb 25, 2013 8:29 pm Post subject: Ground plane diameter

OK, thanks Bob.  It operates on 978 Mhz so I probably could have figured it out by breaking out my ARRL Antenna Book but I guess I was just  a bit on the lazy side.

  

 Bill



 

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

To: aeroelectric-list(at)matronics.com

Sent: Mon, February 25, 2013 8:06:58 PM

Subject: Re: Ground plane diameter



At 03:30 PM 2/25/2013, you wrote:

  	  Quote: 	
		  I'm upgrading avionics in my Glasair and one of the units I'm adding is a Garmin GDL-88 for ADS-B out.  The antenna I'm using is a Comant CI-105 and seeing it's a "plastic" airplane I've been wondering if a 6" diameter copper disc is large enough for the ground plane or should I go a bit larger?  TIA 	




   To understand the workings of ground planes under

   vertical 1/4-wave radiators (like comm, transponder

   and DME) antennas, you need to take a little 'head

   trip'.



   The older brother to a 1/4-wave antenna fed at the

   base is a 1/2-wave antenna fed at the center (aka

   VOR/LOC/GS atennas). The 1/2 wave antenna doesn't

   need a 'ground' because is has useful places to send

   1/2 of the total energy into each of two  identical,

   complimentary radiators.



   Now, take a dipole and turn it up vertically as if

   you wanted to use it for comm. Hmmmm . . . hard to

   attach the coax to it while insulating the hot

   end of the lower element. Okay, bend the lower element

   90 degrees. Now the feed point at the antenna

   center comes down to skin level on the airplane . . .

   but the 'bent' half of the antenna is seriously

   compromised for efficiency as it no longer works

   in concert with its unmodified counterpart.



   Hmmmm . . . how to make the lion's share of the energy

   flow into the freely extended portion of the antenna

   while reducing a wasteful venture onto the

   compromised portion of the antenna? How about adding

   a second compromised element?  Assume the feed point

   impedance of each element is R. Then a dipole in

   extended splendor has a feed point impedance of 2R.



   You've still got R + R with the compromised dipole

   but paralleling two 'crippled' elements at the base

   gives you 1/2R + R. We see that energy fed to

   this network divides with 1/3 going to the compromised

   side and 2/3 to the free element. Let's consider adding

   2 more 'compromised' elements. Now we have 1/4R + R.

   Great! 4/5ths of the energy goes to the working part

   while only 1/5th is left free to roam and be a general

   nuisance to your radiation pattern.



   Now, if you want to squirt your signal off at an

   angle that is closer to the horizon, you can droop

   those elements not unlike the antennas seen  around

   many airports.

  



   Take this exercise to an extreme . . . say 100

   'compromised' elements. Now you get 1/100R + R

   and only 1% of the energy is left free to be

   problematic. Further, 100 compromised elements

   look very close to a solid disk of material having

   a RADIUS equal to the HEIGHT of the free element.

   You sometimes see 100 drooping elements that look

   very much like a cone of solid metal.



   So, getting back to your question, the IDEAL small

   ground plane has a radius equal to the 1/4-wave

   distance for the frequency of interest. In the case

   of transponders, this works out to 300M  meters/sec

   divided by 1050 cycles/second times 39.36 inches/meter

   times 0.25 wavelength and you get 2.8 inches. Twice

   this value is 5.6", the ideal resonant ground plane

   for transponder antennas.



   Making it just a little bigger because you can is

   counter productive. On the other hand, making it

   MUCH bigger (like the belly of a metal airplane)

   and it begins to approximate a non-resonant, infinite

   ground plane which is very good too . . . but a

   a whole different ballgame.



   The short answer is that for a non-conducting

   mounting surface the antenna performs best with

   the idealized, 1/4-wave radius disk. If you

   could mount it to several square feet of aluminum

   it would only slightly better . . . so  slight

   that you would need to measure the difference

   in a well heeled RF lab. So the best recommendation

   is go for the 5.6" disk.



 

  Bob . . . [quote][b]http://www.matronics.com/Navigatrums.matronics.com/" rel=nofollow target=_blank>http://forums.matronics-> [b]

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Feb 26, 2013 6:31 am Post subject: Ground plane diameter

At 10:27 PM 2/25/2013, you wrote:

 	  Quote: 	
		  OK, thanks Bob.  It operates on 978 Mhz so I probably could have 

figured it out by breaking out my ARRL Antenna Book but I guess I 

was just  a bit on the lazy side.


	


    Very good. Yes, 978 MHz does work out to

    a 6" diameter ground plane . . .



   Bob . . .

mrspudandcompany(at)veriz
Guest

Posted: Tue Feb 26, 2013 9:06 am Post subject: Ground plane diameter

 	  Quote: 	
		   

 At 10:27 PM 2/25/2013, you wrote:

>OK, thanks Bob.  It operates on 978 Mhz so I probably could have 

>figured it out by breaking out my ARRL Antenna Book but I guess I 

>was just  a bit on the lazy side.

 

    Very good. Yes, 978 MHz does work out to

    a 6" diameter ground plane . . .


	




            I have seen often that antennas get cut off to tune 

            for maximum radiation.  Is the ground plane as

            critical in dimension as the radiating element?



            Roger



--



Do you have a slow PC? Try a Free scan http://www.spamfighter.com/SLOW-PCfighter?cid=sigen

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Feb 26, 2013 9:35 am Post subject: Ground plane diameter

 	  Quote: 	
		  

            I have seen often that antennas get cut off to tune

            for maximum radiation.  Is the ground plane as

            critical in dimension as the radiating element?



            Roger


	


    I guess it depends on your threshold for assigning

    criticality. I've spent hours in the labs watching

    displays on instruments that dutifully reported

    measurable differences. It's really EASY . . . especially

    for designers and technicians to work in relative

    isolation from practical results to take lots

    of pride and assign criticality to small

    improvements.



    Improvements in the lab go to statistical process

    control. LOTS of tiny improvements in the bits

    and pieces can add up to significance improvements

    in the full up system. At the same time, the guy

    who is fine-tuning his little bit has no control

    over how it will be installed nor will he control

    less than optimum outcomes for associated bits.



    In the world of antennas, the observable effects

    for fabrication are greatest in management

    of radiation pattern. I've seen some plots on

    airframe mounted antennas with deep nulls in

    azimuth plots. Careful tuning for resonance

    is the least part of the recipe for success.

    I.e., optimized SWR and field strength numbers

    can be misleading.



http://tinyurl.com/bea4785



    Bottom line is that taking time to 'trim' a

    ground plan is probably the least productive

    effort. Fortunately, the very short UHF monopole

    antennas are pretty easy to locate to minimize

    airframe distortions of pattern. We are further

    aided by the fact that terrible losses can be

    tolerated in the world of relatively short

    range, line of sight world for aircraft

    communications.



    The only airplanes we ever studied for antenna

    radiation patterns were the big guys who flew

    routinely over water at 41,000 feet with very

    distant radio-horizons. The only pattern work

    I ever witnessed on a small airplane was done

    by Dr. Gordon Wood on a C-172 at Cessna about 1963.

    I don't think the outcome of those studies

    prompted any changes to our legacy installations.



    Don't worry about the ground plane . . .

   Bob . . .

rv7a.n18pf(at)gmail.com
Guest

Posted: Tue Feb 26, 2013 2:31 pm Post subject: Ground plane diameter

It might seem lazy on your part just to get a number - but some of us got an education on WHY that was the number.   So thanks for asking! 

(and of course Thank You Bob for the explanation!) 

- Paul On Feb 25, 2013 10:44 PM, "William Hibbing" <n744bh(at)bellsouth.net (n744bh(at)bellsouth.net)> wrote:[quote] OK, thanks Bob.  It operates on 978 Mhz so I probably could have figured it out by breaking out my ARRL Antenna Book but I guess I was just  a bit on the lazy side.

   

 Bill



 

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

To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)

 Sent: Mon, February 25, 2013 8:06:58 PM

Subject: Re: Ground plane diameter



At 03:30 PM 2/25/2013, you wrote:

   	  Quote: 	
		  I'm upgrading avionics in my Glasair and one of the units I'm adding is a Garmin GDL-88 for ADS-B out.  The antenna I'm using is a Comant CI-105 and seeing it's a "plastic" airplane I've been wondering if a 6" diameter copper disc is large enough for the ground plane or should I go a bit larger?  TIA 	
 



   To understand the workings of ground planes under

   vertical 1/4-wave radiators (like comm, transponder

   and DME) antennas, you need to take a little 'head

   trip'.



   The older brother to a 1/4-wave antenna fed at the

    base is a 1/2-wave antenna fed at the center (aka

   VOR/LOC/GS atennas). The 1/2 wave antenna doesn't

   need a 'ground' because is has useful places to send

   1/2 of the total energy into each of two  identical,

   complimentary radiators.



   Now, take a dipole and turn it up vertically as if

   you wanted to use it for comm. Hmmmm . . . hard to

   attach the coax to it while insulating the hot

   end of the lower element. Okay, bend the lower element

    90 degrees. Now the feed point at the antenna

   center comes down to skin level on the airplane . . .

   but the 'bent' half of the antenna is seriously

   compromised for efficiency as it no longer works

    in concert with its unmodified counterpart.



   Hmmmm . . . how to make the lion's share of the energy

   flow into the freely extended portion of the antenna

   while reducing a wasteful venture onto the

    compromised portion of the antenna? How about adding

   a second compromised element?  Assume the feed point

   impedance of each element is R. Then a dipole in

   extended splendor has a feed point impedance of 2R.



   You've still got R + R with the compromised dipole

   but paralleling two 'crippled' elements at the base

    gives you 1/2R + R. We see that energy fed to

   this network divides with 1/3 going to the compromised

   side and 2/3 to the free element. Let's consider adding

   2 more 'compromised' elements. Now we have 1/4R + R.

    Great! 4/5ths of the energy goes to the working part

   while only 1/5th is left free to roam and be a general

   nuisance to your radiation pattern.



   Now, if you want to squirt your signal off at an

    angle that is closer to the horizon, you can droop

   those elements not unlike the antennas seen  around

   many airports.

  



   Take this exercise to an extreme . . . say 100

    'compromised' elements. Now you get 1/100R + R

   and only 1% of the energy is left free to be

   problematic. Further, 100 compromised elements

   look very close to a solid disk of material having

    a RADIUS equal to the HEIGHT of the free element.

   You sometimes see 100 drooping elements that look

   very much like a cone of solid metal.



   So, getting back to your question, the IDEAL small

   ground plane has a radius equal to the 1/4-wave

    distance for the frequency of interest. In the case

   of transponders, this works out to 300M  meters/sec

   divided by 1050 cycles/second times 39.36 inches/meter

   times 0.25 wavelength and you get 2.8 inches. Twice

   this value is 5.6", the ideal resonant ground plane

   for transponder antennas.

 

   Making it just a little bigger because you can is

   counter productive. On the other hand, making it

   MUCH bigger (like the belly of a metal airplane)

   and it begins to approximate a non-resonant, infinite

    ground plane which is very good too . . . but a

   a whole different ballgame.



   The short answer is that for a non-conducting

   mounting surface the antenna performs best with

   the idealized, 1/4-wave radius disk. If you

    could mount it to several square feet of aluminum

   it would only slightly better . . . so  slight

   that you would need to measure the difference

   in a well heeled RF lab. So the best recommendation

   is go for the 5.6" disk.



 

  Bob . . .  	  Quote: 	
		  http://www.matronics.com/Navigatrums.matronics.com/" rel=nofollow target=_blank>http://forums.matronics-> [url=http://www.matronics.com/contribution][/url] 	
 

  	  Quote: 	
		  



ist" target="_blank">http://www.matronics.com/Navigator?AeroElectric-List

tp://forums.matronics.com

_blank">http://www.matronics.com/contribution



	


[b]

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Feb 26, 2013 4:26 pm Post subject: Ground plane diameter

At 04:30 PM 2/26/2013, you wrote:



 	  Quote: 	
		  It might seem lazy on your part just to get a number

- but some of us got an education on WHY that was the

number.   So thanks for asking!



(and of course Thank You Bob for the explanation!)



- Paul


	


   My pleasure sir. I know some folks may feel

   a bit over-informed but I'll ask that they

   keep in mind that this list has about 1600

   subscribers (at last count 6 months ago).

   Interest in answers has to span a wide

   range and I try to address it.



   Not trying to preach or 'stuff' anyone

   with data they don't wish to possess . . .



   Bob . . .

bob.verwey(at)gmail.com
Guest

Posted: Thu Feb 28, 2013 1:31 am Post subject: Ground plane diameter

If we consider the simple whip antenna for our VHF comms, what is the best trimmed length for the antenna part and the ground plane diameter to optimise the frequencies in the early '120's? 



Best..

 Bob Verwey



On 26 February 2013 19:02, R. curtis <mrspudandcompany(at)verizon.net (mrspudandcompany(at)verizon.net)> wrote:

 [quote]--> AeroElectric-List message posted by: "R. curtis" <mrspudandcompany(at)verizon.net (mrspudandcompany(at)verizon.net)>

  

 

  	  Quote: 	
		   

 At 10:27 PM 2/25/2013, you wrote:

  	  Quote: 	
		   OK, thanks Bob.  It operates on 978 Mhz so I probably could have figured it out by breaking out my ARRL Antenna Book but I guess I was just  a bit on the lazy side.

 	
 

    Very good. Yes, 978 MHz does work out to

    a 6" diameter ground plane . . .

 	
 

 

            I have seen often that antennas get cut off to tune            for maximum radiation.  Is the ground plane as

            critical in dimension as the radiating element?

 

            Roger

 

 --

 

 Do you have a slow PC? Try a Free scan http://www.spamfighter.com/SLOW-PCfighter?cid=sigen

 

 

 

 ====================================

 -List" target="_blank">http://www.matronics.com/Navigator?AeroElectric-List

 ====================================

 http://forums.matronics.com

 ====================================

 le, List Admin.

 ="_blank">http://www.matronics.com/contribution

 ====================================

 

 

 

 [b]

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Feb 28, 2013 6:58 am Post subject: Ground plane diameter

At 03:29 AM 2/28/2013, you wrote:

 	  Quote: 	
		  If we consider the simple whip antenna for our VHF comms, what is 

the best trimmed length for the antenna part and the ground plane 

diameter to optimise the frequencies in the early '120's?


	


   Center of the VHF comm spectrum is (118+135)/2 or 127.5 MHz



   Free space full wavelength in meters is 300/127.5 = 2.35M



   2.35M x 39.34 in/meter yields 92"



   1/4 wave radials (or antennas) at 127.5 are

   92/4 or 23".



   Bob . . .

bob.verwey(at)gmail.com
Guest

Posted: Thu Feb 28, 2013 8:13 am Post subject: Ground plane diameter

Thanks Bob,



Care to elaborate on the ground plane a little? If the structure of the aircraft is 'Cub-like' steel tubing, and one mounts the antenna on the roof, is it sufficient to use the airframe as the groundplane?

 



Bob Verwey

On 28 February 2013 16:53, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

 [quote]--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>

  

 At 03:29 AM 2/28/2013, you wrote:

  	  Quote: 	
		   If we consider the simple whip antenna for our VHF comms, what is the best trimmed length for the antenna part and the ground plane diameter to optimise the frequencies in the early '120's?

 	
 

   Center of the VHF comm spectrum is (118+135)/2 or 127.5 MHz

 

   Free space full wavelength in meters is 300/127.5 = 2.35M

 

   2.35M x 39.34 in/meter yields 92"

 

   1/4 wave radials (or antennas) at 127.5 are

   92/4 or 23".

 

 

 

   Bob . . . 

 

 ====================================

 -List" target="_blank">http://www.matronics.com/Navigator?AeroElectric-List

 ====================================

 http://forums.matronics.com

 ====================================

 le, List Admin.

 ="_blank">http://www.matronics.com/contribution

 ====================================

 

 

 

 [b]

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Feb 28, 2013 9:06 am Post subject: Ground plane diameter

At 10:10 AM 2/28/2013, you wrote:

 	  Quote: 	
		  Thanks Bob,



Care to elaborate on the ground plane a little? If the structure of 

the aircraft is 'Cub-like' steel tubing, and one mounts the antenna 

on the roof, is it sufficient to use the airframe as the groundplane?


	


   ANY conductive material can be brought into service

   as a 'ground'. Given our unique line-of-sight, short-range

   expectations for radio communications, a wet-string would

   probably serve 96% of your communications expectations.



   Consider the lowly hand-held. Talk about compromised

   ground planes!! The rubber duck in a sweaty fist works

   for some situations, other situations (mostly driven by

   customer's willingness to pay) are optimized to the

   best-we-know-how-to-do. Most of us will secure happiness with

   some intermediate but decidedly less expensive configuration.



   ANY combination you choose to try should be first tailored

   for lowest possible SWR over the range of interest. The

   transmitter has no idea what's at the other end of the

   feedline. Gross efficiency and/or radiation patterns are

   separate issues not easily measured and massaged.



   Are there things we could do that are 'better' than

   using a rag-covered-tube ground plane? Sure. Would the

   guy at the other end of the link know the difference?

   Probably not. This is but one of several advantages

   we enjoy over the drivers of TC iron, we can try it.

   If found insufficient to design goals, do something

   different.



   Bob . . .

FisherPaulA(at)johndeere.
Guest

Posted: Thu Feb 28, 2013 9:37 am Post subject: Ground plane diameter

Iâ€™d like to try to answer this: 

  

300 million meters per second is roughly the speed of light â€“ also about the speed the radio waves propagate.  Dividing this by the frequency in megahertz gives  you the wave length. So 300,000,000/127,500,000 = 2.35 meters.  

  

  

seems like this was on the test for my ham licenseâ€¦ surprising I still remember it! 

  

Paul Fisher 

  

  

From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Christopher Cee Stone

 Sent: Thursday, February 28, 2013 11:07 AM

 To: aeroelectric-list(at)matronics.com

 Subject: Re: AeroElectric-List: Ground plane diameter 

  

Bob...  

  

  

I follow your calcs and the underlying physics until I see the 300/127.5 = 2.35M.  Where is the 300 from? What does it represent? 

  

  

  

Always learning! 

  

  

  

Chris Stone

cyav8r(at)yahoo.com
Guest

Posted: Thu Feb 28, 2013 9:55 am Post subject: Ground plane diameter

Then would be the recommendation for a more modern design that is all carbon fiber?  The carbon is conductive, but absorbs radiation instead of reflecting it from what I understand.  Go with a foil circle or strips of the appropriate diameter on the outside of the carbon, but under the paint?  



Thanks



Paul





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

 To: aeroelectric-list(at)matronics.com 

 Sent: Thursday, February 28, 2013 11:05 AM

 Subject: Re: Ground plane diameter

  

 

 --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>



At 10:10 AM 2/28/2013, you wrote:

 	  Quote: 	
		   Thanks Bob,

 

 Care to elaborate on the ground plane a little? If the structure of the aircraft is 'Cub-like' steel tubing, and one mounts the antenna on the roof, is it sufficient to use the airframe as the groundplane?


	


  ANY conductive material can be brought into service

  as a 'ground'. Given our unique line-of-sight, short-range

  expectations for radio communications, a wet-string would

&nbsp========

rv8iator(at)gmail.com
Guest

Posted: Thu Feb 28, 2013 10:01 am Post subject: Ground plane diameter

Ahhh... Â Yes.



Still mired in English units 186,000 miles per second.

Thanks!

chris stone



On Thu, Feb 28, 2013 at 9:34 AM, Fisher Paul A. <FisherPaulA(at)johndeere.com (FisherPaulA(at)johndeere.com)> wrote:

 [quote]        

Iâ€™d like to try to answer this: 

Â  

300 million meters per second is roughly the speed of light â€“ also about the speed the radio waves propagate.Â  Dividing this by the frequency in megahertz gives  you the wave length. So 300,000,000/127,500,000 = 2.35 meters.  

Â  

Â  

seems like this was on the test for my ham licenseâ€¦ surprising I still remember it!  

Â  

Paul Fisher 

Â  

Â  

From: owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com) [mailto:owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com)] On Behalf Of Christopher Cee Stone

 Sent: Thursday, February 28, 2013 11:07 AM

 To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)

 Subject: Re: Ground plane diameter 

Â  

Bob...  

Â  

  

I follow your calcs and the underlying physics until I see the 300/127.5 = 2.35M. Â Where is the 300 from? What does it represent? 

  

Â  

  

Always learning! 

  

Â  

  

Chris Stone 

  

Â  

 



 

  [b]

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Feb 28, 2013 10:36 am Post subject: Ground plane diameter

At 11:48 AM 2/28/2013, you wrote:

 	  Quote: 	
		  Then would be the recommendation for a more modern design that is 

all carbon fiber?  The carbon is conductive, but absorbs radiation 

instead of reflecting it from what I understand.  Go with a foil 

circle or strips of the appropriate diameter on the outside of the 

carbon, but under the paint?


	


   That's a whole other can of worms. The carbon fiber

   is, as you've described, pretty lossy stuff. Yeah, it

   is conductive but much of electrical energy flowing

   through a carbon matrix is converted to heat.



   Trying to create idealized ground planes over the

   carbon and under the paint is exceedingly expensive

   and problematic for affecting structural integrity

   of the shell.



   At HBC, non-resonant ground planes were bonded to the

   inside surface of the fuselage shell. Relatively

   inexpensive and the flight test results deemed them

   adequate to the task.



   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Feb 28, 2013 10:57 am Post subject: Ground plane diameter

At 11:34 AM 2/28/2013, you wrote:

 	  Quote: 	
		  Iâ€™d like to try to answer this:



300 million meters per second is roughly the 

speed of light – also about the speed the radio 

waves propagate.  Dividing this by the frequency 

in megahertz gives you the wave length. So 

300,000,000/127,500,000 = 2.35 meters.

seems like this was on the test for my ham 

license… surprising I still remember it!>


	


   Yeah, pretty cool stuff. First learned to do those

   calculations on a slide rule about 60 years

   ago . . .



   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Feb 28, 2013 11:07 am Post subject: Ground plane diameter

I'd forgotten about a compendium of antenna articles

that were waiting to be posted to the website. I just

put them up where they can be downloaded and inquiring

minds can exploit as appropriate:



http://tinyurl.com/d2ql8lw



   Bob . . .

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