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armywrights(at)adelphia.n
Guest

Posted: Sat Apr 22, 2006 1:21 pm Post subject: antenna

On Comant's spec sheets for DME/Transponder antennae, what is the

significance of "Power RF?"



 



Rob

nuckollsr(at)cox.net
Guest

Posted: Sat Apr 22, 2006 3:22 pm Post subject: antenna

At 04:08 PM 4/22/2006 -0500, you wrote:



 	  Quote: 	
		  

<armywrights(at)adelphia.net>



On Comant's spec sheets for DME/Transponder antennae, what is the

significance of "Power RF?"


	


   For antennas, it's the maxiumum rated po

 	  Quote: 	
		  



Rob





--




	




        Bob . . .

      < What is so wonderful about scientific truth...is that >

      < the authority which determines whether there can be   >

      < debate or not does not reside in some fraternity of   >

      < scientists; nor is it divine. The authority rests     >

      < with experiment.                                      >

      <                            --Lawrence M. Krauss       >

endspeed(at)yahoo.com
Guest

Posted: Sun Apr 23, 2006 6:33 am Post subject: antenna

--- "Robert G. Wright" <armywrights(at)adelphia.net>

wrote:



 	  Quote: 	
		   

 Wright" <armywrights(at)adelphia.net>

 

 On Comant's spec sheets for DME/Transponder

 antennae, what is the

 significance of "Power RF?"

 

  

 

 Rob

 

 

 

 

 



 browse

 Subscriptions page,

 FAQ,

 http://www.matronics.com/Navigator?AeroElectric-List

 Admin.

endspeed(at)yahoo.com
Guest

Posted: Sun Apr 23, 2006 6:33 am Post subject: antenna

--- "Robert G. Wright" <armywrights(at)adelphia.net>

wrote:



 	  Quote: 	
		   

 Wright" <armywrights(at)adelphia.net>

 

 On Comant's spec sheets for DME/Transponder

 antennae, what is the

 significance of "Power RF?"

 

  

 

 Rob

 

 

 

 

 



 browse

 Subscriptions page,

 FAQ,

 http://www.matronics.com/Navigator?AeroElectric-List

 Admin.

nuckollsr(at)cox.net
Guest

Posted: Sun Apr 23, 2006 9:23 am Post subject: antenna

At 04:08 PM 4/22/2006 -0500, you wrote:



 	  Quote: 	
		  

<armywrights(at)adelphia.net>



On Comant's spec sheets for DME/Transponder antennae, what is the

significance of "Power RF?"



Rob


	




    Hmmm . . . seems my reply was truncated. For antennas, there's

    a design limit for the maximum power you can expect it to

    handle.  For example, a simple DME/Transponder antenna for

    mounting to the bottom of an airplane could be severely

    taxed at say 10,000 watts. It could be a current issue

    where some part of the antenna might be overheating and

    be damaged (not a problem with DME/Transponder antennas

    because while PEAK power is perhaps 100-200 watts, the average

    power is measured in milliwatts. If it's a voltage issue

    (gaps in construction or capacitors arc over) then peak

    power is a significant concern irrespective of

    average power.



    In any case, a DME/Transponder antenna you purchase for

    use on an aircraft isn't going to be at-risk for damage

    by any radio installed for that purpose at the power levels

    commonly supplied. A 50-ohm antenna accepting 250 watts

    of power sees peak currents on the order of 2.5 amps

    and peak voltages on the order of 110 volts. Generally

    not a big thing in the aviation antenna world.



    The same company may well make antennas rated in the

    killowatts where such things are a design challenge.

    They may have a data sheet format that says

    "tho shalt put a power rating on thy product"

    so even the lowly DME/Transponder antenna gets a power

    rating.



    This gives rise to the neophyte's dilemma, "Gee, there's

    a power rating stated for this product I might want to

    buy for my airplane . . . how and why would I consider

    this as significant for my buy-decision?" The answer

    in this case is, "No big deal."



    Bob . . .



      < What is so wonderful about scientific truth...is that >

      < the authority which determines whether there can be   >

      < debate or not does not reside in some fraternity of   >

      < scientists; nor is it divine. The authority rests     >

      < with experiment.                                      >

      <                            --Lawrence M. Krauss       >

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Sun Apr 23, 2006 11:08 am Post subject: antenna

Robert G. Wright wrote:

 	  Quote: 	
		   

 

 On Comant's spec sheets for DME/Transponder antennae, what is the

 significance of "Power RF?"


	


Transmitting antennas are usually rated for how much transmitter output

power they can handle. Remember that transponders and DMEs have

transmitters and transmit with peak power levels on the order of 200-300

watts. They transmit in short bursts so that the average power is low

but still, the peak voltages and currents are those of the 300W level.

This can cause arcing internally to the antenna if it isn't rated for

this power level.



But if the antenna says it is for a DME or transponder, you are pretty

safe using it for that function.



-- 

Brian Lloyd                         361 Catterline Way

brian-yak at lloyd dot com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

- Antoine de Saint-Exupery

_________________
Brian Lloyd
brian-yak at lloyd dot com
+1.916.367.2131 (voice) +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery

armywrights(at)adelphia.n
Guest

Posted: Sun Apr 23, 2006 12:35 pm Post subject: antenna

Bob, you're so quick on replies, you even beat me to labeling myself the

neophyte that I am!  I'm just trying to wrap myself around all the info out

there on airframe and panel wiring that Revision 11 just can't hold.  I'm

weighing the desire to do all my own wiring (time and learning) against

farming the panel out to $omeone el$e just to have it correct.  Too bad

there're no avionics seminars around my area for the next foreseeable

future....

Rob

 	  Quote: 	
		  

On Comant's spec sheets for DME/Transponder antennae, what is the

significance of "Power RF?"



Rob


	




    Hmmm . . . seems my reply was truncated. For antennas, there's

    a design limit for the maximum power you can expect it to

    handle.  For example, a simple DME/Transponder antenna for

    mounting to the bottom of an airplane could be severely

    taxed at say 10,000 watts. It could be a current issue

    where some part of the antenna might be overheating and

    be damaged (not a problem with DME/Transponder antennas

    because while PEAK power is perhaps 100-200 watts, the average

    power is measured in milliwatts. If it's a voltage issue

    (gaps in construction or capacitors arc over) then peak

    power is a significant concern irrespective of

    average power.



    In any case, a DME/Transponder antenna you purchase for

    use on an aircraft isn't going to be at-risk for damage

    by any radio installed for that purpose at the power levels

    commonly supplied. A 50-ohm antenna accepting 250 watts

    of power sees peak currents on the order of 2.5 amps

    and peak voltages on the order of 110 volts. Generally

    not a big thing in the aviation antenna world.



    The same company may well make antennas rated in the

    killowatts where such things are a design challenge.

    They may have a data sheet format that says

    "tho shalt put a power rating on thy product"

    so even the lowly DME/Transponder antenna gets a power

    rating.



    This gives rise to the neophyte's dilemma, "Gee, there's

    a power rating stated for this product I might want to

    buy for my airplane . . . how and why would I consider

    this as significant for my buy-decision?" The answer

    in this case is, "No big deal."



    Bob . . .



      < What is so wonderful about scientific truth...is that >

      < the authority which determines whether there can be   >

      < debate or not does not reside in some fraternity of   >

      < scientists; nor is it divine. The authority rests     >

      < with experiment.                                      >

      <                            --Lawrence M. Krauss       >

simon.miles(at)skynet.be
Guest

Posted: Sun Apr 23, 2006 12:37 pm Post subject: antenna

I'm intrigued. Why does a transponder or DME draw such high power? My 

radio only draws about 5 watts and that seems to work perfectly well - 

or is the peak draw actually much higher?

Simon Miles.

Brian Lloyd wrote:

 	  Quote: 	

 Robert G. Wright wrote:

> 

>

> On Comant's spec sheets for DME/Transponder antennae, what is the

> significance of "Power RF?"

 Transmitting antennas are usually rated for how much transmitter output

 power they can handle. Remember that transponders and DMEs have

 transmitters and transmit with peak power levels on the order of 200-300

 watts. They transmit in short bursts so that the average power is low

 but still, the peak voltages and currents are those of the 300W level.

 This can cause arcing internally to the antenna if it isn't rated for

 this power level.

 But if the antenna says it is for a DME or transponder, you are pretty

 safe using it for that function.

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Sun Apr 23, 2006 1:39 pm Post subject: antenna

simon miles wrote:

 	  Quote: 	
		   

 

 I'm intrigued. Why does a transponder or DME draw such high power? My 

 radio only draws about 5 watts and that seems to work perfectly well - 

 or is the peak draw actually much higher?


	


It doesn't draw high power. It is just that it transmits very short

bursts of high power so while the peak power is high, the average power

(which is what your power bus has to deliver to the radio) is very low.



Think of it this way. It might transmit with 100W for 1/100th of a

second every second. The peak power is 100W but the average power is 1W.

The durations and rates are different than that in real life but it

gives you the idea how it works.



-- 

Brian Lloyd                         361 Catterline Way

brian-yak at lloyd dot com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

- Antoine de Saint-Exupery

nuckollsr(at)cox.net
Guest

Posted: Sun Apr 23, 2006 2:28 pm Post subject: antenna

At 03:33 PM 4/23/2006 -0500, you wrote:



 	  Quote: 	
		  

<armywrights(at)adelphia.net>



Bob, you're so quick on replies, you even beat me to labeling myself the

neophyte that I am!  I'm just trying to wrap myself around all the info out

there on airframe and panel wiring that Revision 11 just can't hold.  I'm

weighing the desire to do all my own wiring (time and learning) against

farming the panel out to $omeone el$e just to have it correct.  Too bad

there're no avionics seminars around my area for the next foreseeable

future....


	




   We are ALL neophytes at many things. I presume your presence

   here on the List is search out useful things to apply to your

   decision making and/or to enhance your abilities to take on

   new tasks. It's my pleasure and that of many others to share

   what we've learned toward  your goals.



    Bob . . .

nuckollsr(at)cox.net
Guest

Posted: Sun Apr 23, 2006 2:53 pm Post subject: antenna

At 08:08 PM 4/23/2006 -0700, you wrote:

 	  Quote: 	

simon miles wrote:

 > 

 <simon.miles(at)skynet.be>

 >

 > I'm intrigued. Why does a transponder or DME draw such high power? My

 > radio only draws about 5 watts and that seems to work perfectly well -

 > or is the peak draw actually much higher?

It doesn't draw high power. It is just that it transmits very short

bursts of high power so while the peak power is high, the average power

(which is what your power bus has to deliver to the radio) is very low.

Think of it this way. It might transmit with 100W for 1/100th of a

second every second. The peak power is 100W but the average power is 1W.

The durations and rates are different than that in real life but it

gives you the idea how it works.

   Brian nails it. Consider that power is a rate thing and does not

   consider duration. For example, cruising down the road may require

   40-50 horsepower from your engine . . . but how does that translate

   to energy? To speak of energy, you must consider duration. Driving

   500 miles might take ten hours . . . so while the power was 50 h.p.,

   the energy was 500 horsepower-hours.

   You can have a 100 watt lightbulb on the ceiling that you

   turn on for one second out of each hour. Peak power is 100

   watts, energy is 100/3600 watt-hours or 1/36th of a watt-hour.

   Your transponder puts out a stream of 0.45 microsecond wide

   pulses at 100W, or what ever the "power rating" of your transponder

   is.

See http://www.airsport-corp.com/modec.htm

   The strings happen over a span of 21 uS and repeats several times

   each time the REPLY light on your transponder lights up. One might

   say that the AVERAGE power for a reply of all "1" in the bit stream

   approaches 50 watts . . . but this is still very periodic and even when

   your're being painted by several radar sites, the average power over

   say 10 seconds is less than 1 watt which accounts for about 100 millampers

   of the input power to your transponder . . . the rest being lost

   in running associated circuitry and losses in the transmitter's high

   power output stage.

   Tying this back to the antenna power rating question, knowing that

   peak power is as much as 200W, the designer might have some voltage 

issues to

   consider but from an average power handling perspective, current

   stresses to the antenna are trivial.

   Bob . . .

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