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Antennas general

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frank.hinde(at)hp.com
Guest

Posted: Wed Jul 26, 2006 9:02 am Post subject: Antennas general

On my Vans kit they provided a wingtip NAV antenna which is just a

strip of copper foil. Do not suggest how one is supposed to ground it to

the airframe.



I assume one has to ground the coax braid to the wing somehow??



Also I intend to run my marker beacon antenna (40" lentgh of stripped

coax) in the bottom of my cowl. Assuming this will work do I need to

bond that coax to the firewall or similar?



Thanks



Frank



Rv 7a...Finishing..No really I am finishing..

recapen(at)earthlink.net
Guest

Posted: Wed Jul 26, 2006 10:20 am Post subject: Antennas general

Frank,



For the wingtip NAV, IIRC the coax shield is to be grounded with the shield approx where it ends and the foil begins.



For my marker beacon, I am using bulkhead fittings to penetrate the firewall so I am considering mine grounded to the SSFirewall.



I'm gonna use the 40" stripped coax on the bottom of my cowl too - along with another stripped length (gotta figure out the math) for my AM/FM/MP3 player.



When you're really finished and flying - come visit N06 Laurel, DE....



Ralph



--

frank.hinde(at)hp.com
Guest

Posted: Wed Jul 26, 2006 10:59 am Post subject: Antennas general

Now there is an idea...I just passed my RG56 thru a grommet in the

firewall but a bulkhead fitting would take care of the grounding...I

have not fire sealed it yet so I might do the same thing...assuming

Radio Shack sells the fittings of course.



Thanks Ralph



Frank 



--

brian

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

Posted: Wed Jul 26, 2006 12:10 pm Post subject: Antennas general

On Jul 26, 2006, at 12:58 PM, Hinde, Frank George (Corvallis) wrote:



 	  Quote: 	
		   

 (Corvallis)" <frank.hinde(at)hp.com>



  On my Vans kit they provided a wingtip NAV antenna which is just a

 strip of copper foil. Do not suggest how one is supposed to ground  

 it to

 the airframe.



 I assume one has to ground the coax braid to the wing somehow??



 Also I intend to run my marker beacon antenna (40" lentgh of stripped

 coax) in the bottom of my cowl. Assuming this will work do I need to

 bond that coax to the firewall or similar?


	


Not really. A 50W transmitter shooting its signal at you using a  

directional antenna when you are less than 2000' away does not  

require much from the receiver and its antenna. The signal level is  

so high that making a perfect antenna is not necessary.



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-Exupéry

_________________
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

recapen(at)earthlink.net
Guest

Posted: Wed Jul 26, 2006 2:26 pm Post subject: Antennas general

They might - but digi-key does for sure.......



--

europa flugzeug fabrik

Joined: 13 Feb 2006
Posts: 65
Location: North Coast, USA

Posted: Wed Jul 26, 2006 3:58 pm Post subject: Re: Antennas general

 	  brian wrote: 	
		  A 50W transmitter shooting its signal at you using a directional antenna when you are less than 2000' away does not require much from the receiver and its antenna. 	


I believe theyâ€™re as little as 2.5W, though as highly directional, the moral equivalent of higher power relative to like a COM.  Perhaps you are referring to that.



Also, the sensitivity of the receiver isnâ€™t good, maybe 200 times less sensitive than  a COM.  So, the antenna has to be reasonably good.  I wonder if we could use wire or copper tape to fake an equivalent of a sled antenna.  One end to shield, center wire about 10â€ down or wherever, but we need a ramp tester to tune it.  Or rig it up in the car, and find a marker shed we can drive up close to.  A coax monopole w/o ground plane as proposed will probably be OK.



Fred F.

nuckollsr(at)cox.net
Guest

Posted: Thu Jul 27, 2006 5:03 am Post subject: Antennas general

At 04:58 PM 7/26/2006 -0700, you wrote:



 	  Quote: 	
		  

<n3eu(at)comcast.net>

brian wrote:

 > A 50W transmitter shooting its signal at you using a directional 

 antenna when you are less than 2000' away does not require much from the 

 receiver and its antenna.



I believe theyâ€™re as little as 2.5W, though as highly directional, the 

moral equivalent of higher power relative to like a COM.  Perhaps you are 

referring to that.



Also, the sensitivity of the receiver isnâ€™t good, maybe 200 times less 

sensitive than  a COM.  So, the antenna has to be reasonably good.  I 

wonder if we could use wire or copper tape to fake an equivalent of a sled 

antenna.  One end to shield, center wire about 10â€ down or wherever, but 

we need a ramp tester to tune it.  Or rig it up in the car, and find a 

marker shed we can drive up close to.  A coax monopole w/o ground plane as 

proposed will probably be OK.



Fred F.


	


Lets put some rough orders of magnitude numbers to

this discussion. Assuming 2.5 W transmitter driving

a corner reflector (lets assume 3db gain) for an

ERP of 5 watts, let's plug into:



http://www.megalithia.com/elect/fieldstr.html



With an ERP of .005 Kw and distance of .2 KM.

Leave the channel defaulted at CH44.



This calculator is for UHF frequencies the the

performance at 75 MHz would be only slightly different

due to tiny differences in path losses.



The calculator says we can expect a field strength

on the order of 80 dBuV at .2 Km above this marker

site.



Go to:



http://www.radioing.com/eengineer/rfcalc.html



and enter 80 (dBuV) before punching the box in the lower

right column for DbUv -> Volts conversion and we get:



0.01 volts, or 10,000 microvolts.



Marker beacon receiver sensitivity is on the order of

1500 uV in the LO SENS position and 200 uV in the

HI SENS position. So barring errors in data or logic

it seems that there's a LOT of head-roon for loss of

antenna efficiency.



I've had a number of builders in glass/epoxy airplanes

simply lay a 40" piece of wire out in the tailcone

and run a coax to the marker receiver report excellent

results.



But the bottom line is that what ever one installs that

departs from the installation instructions (hence departures

from the manufacturer's expectations) the installation should

be flight checked by overflying a marker beacon facility

at various altitudes. Returning to



http://www.megalithia.com/elect/fieldstr.html



Enter 1.5 KM into the distance box (5x higher than anything

we would expect to do in a real approach) and we get

62 dBuV field strength. Which converts to a potential

signal level of 1200 uV to a receiver in an IDEAL installation.



Hmmmm . . . one would probably not expect even the best of

installations to function at 5,000 AGL in LO sensitivity but

it should come back alive when you select the HI sensitivity.



A little bit of flight testing is all it takes to see how much

headroom your installation possesses. Data-in-hand trumps

un-quantified supposition every time. The above exercise suggests

that considerable degradation of gross antenna performance is

tolerable and worthy of further exploration.



Bob . . .

sportav8r(at)aol.com
Guest

Posted: Thu Jul 27, 2006 5:34 am Post subject: Antennas general

While we're discussing dB's, I note that the installation instructions for my Garmin GMA 340 audio panel mention several times a feature provinding "10 times gain (20 dB)" for the entertainment channel input.  I have labored all my life under the impression that 10dB was 10x gain, and 20 dB was 100x gain.  It seems unlikely that the people who design this stuff professionally know more about decibels and power gain than a radio hobbyist does, so it's safe to assume I'm the one who is missing something.  What gives?

    

   Sorry to hijack an antenna thread for this, Bob.  But I've just got to get this straight before I go nuts 

    

   -Bill B 

    

  

 --

Hopperdhh(at)aol.com
Guest

Posted: Thu Jul 27, 2006 5:52 am Post subject: Antennas general

In a message dated 7/27/2006 9:39:55 A.M. Eastern Daylight Time,  sportav8r(at)aol.com writes:

  	  Quote: 	
		     While we're discussing dB's, I note that the installation instructions    for my Garmin GMA 340 audio panel mention several times a feature provinding    "10 times gain (20 dB)" for the entertainment channel input.  I have    labored all my life under the impression that 10dB was 10x gain, and 20 dB was    100x gain.  It seems unlikely that the people who design this stuff    professionally know more about decibels and power gain than a radio hobbyist    does, so it's safe to assume I'm the one who is missing something.     What gives?

    

   Sorry to hijack an antenna thread for this, Bob.  But I've just got    to get this straight before I go nuts 

    

   -Bill B 

    

	


 

 Bill,

  

 You are correct for POWER gain.  For VOLTAGE gain Garmin is  right.

  

 Db=10 log (P1/P2)

  

 Db=20 log (V1/V2)

  

 Dan Hopper

 K9WEK

 RV-7A

nuckollsr(at)cox.net
Guest

Posted: Thu Jul 27, 2006 8:37 am Post subject: Antennas general

At 09:58 AM 7/26/2006 -0700, you wrote:



 	  Quote: 	
		  

<frank.hinde(at)hp.com>



  On my Vans kit they provided a wingtip NAV antenna which is just a

strip of copper foil. Do not suggest how one is supposed to ground it to

the airframe.



I assume one has to ground the coax braid to the wing somehow??


	


   How is the foil installed? Does it begin right at the edge of

   the tip fairing such that transition from coax to antenna is

   closely located to metallic portions of the wing? If so, ground

   the coax shield to the nearest practical wing-metal.

 	  Quote: 	
		  Also I intend to run my marker beacon antenna (40" lentgh of stripped

coax) in the bottom of my cowl. Assuming this will work do I need to

bond that coax to the firewall or similar?


	


   Here's where having access to a piece of test equipment is

   a real help! An MFJ-259 antenna analyzer (See:



http://www.mfjenterprises.com/products.php?prodid=MFJ-259B )



   would allow you to run say 10" of straight wire, coil 20"

   or so around a piece of plastic or wooden dowel, then extend

   the remainder out straight for an overall length of 20"

   or so. Then use the antenna analyzer to look at the characteristics

   of this shortened antenna. You'll find that it resonates lower

   than 75 Mhz. Trim the 10" extension beyond the coil to bring

   the antenna up to 75 Mhz then glass over what remains.



   Bob . . .

sportav8r(at)aol.com
Guest

Posted: Thu Jul 27, 2006 11:25 am Post subject: Antennas general

Aw, shoot!  Make that P=E^2/R.  I knew better than that.  Hit "send" too quickly.

    

   -Stormy 

    

  

 --

sportav8r(at)aol.com
Guest

Posted: Thu Jul 27, 2006 11:25 am Post subject: Antennas general

Ah, the old P=E^2*R ploy.   I see now.  Thanks. 

    

  

 --

Dale Ensing

Joined: 11 Jan 2006
Posts: 571
Location: Aero Plantation Weddington NC

Posted: Thu Jul 27, 2006 3:42 pm Post subject: Antennas general

Are you sure it is not E=mc2      ;<)

  	  Quote: 	
		     



   Aw, shoot!  Make that P=E^2/R.  I knew better than that.     Hit "send" too quickly.

    

   -Stormy 

    

 

DO NOT  ARCHIEVE

_________________
Dale Ensing
RV-6A
Aero Plantation
Weddington NC

sportav8r(at)aol.com
Guest

Posted: Thu Jul 27, 2006 5:35 pm Post subject: Antennas general

Dale, you may have something there... ask the patent office 

    

   do not archive 

    

  

 --

brian

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

Posted: Fri Jul 28, 2006 5:00 am Post subject: Antennas general

On Jul 27, 2006, at 9:28 AM, sportav8r(at)aol.com wrote:



 	  Quote: 	
		   While we're discussing dB's, I note that the installation  

 instructions for my Garmin GMA 340 audio panel mention several  

 times a feature provinding "10 times gain (20 dB)" for the  

 entertainment channel input.  I have labored all my life under the  

 impression that 10dB was 10x gain, and 20 dB was 100x gain.  It  

 seems unlikely that the people who design this stuff professionally  

 know more about decibels and power gain than a radio hobbyist does,  

 so it's safe to assume I'm the one who is missing something.  What  

 gives?


	


10dB is a ten-fold increase in *power*.



Since power is V^2/R if you increase voltage by a factor of 10 you  

increase power by a factor of 100 (10x10). A 100-fold increase in  

power is 20dB.



A gain of 10 (voltage increased ten times) results in a power gain of  

20dB.



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-Exupéry

altoq(at)cebridge.net
Guest

Posted: Fri Jul 28, 2006 11:08 am Post subject: Antennas general

NOT RV Related



Just as a point of intrest, if you want V²2/R, turn Number Lock on, hold 

down Alt key and type 0178 on the Number Pad. When you release the Alt key 

the ² pops up. Degrees (X°) is 0176 and (X³) is 0179. This is done through 

Charicter Map and there are many more. Check it out in System Tools. It is 

an automatic install for Windows XP but you might have to install it in 

98/SE. Its on the Windows Disk.



John D.



Do Not Archive

 	  Quote: 	
		   Since power is V^2/R if you increase voltage by a factor of 10 you 

 increase power by a factor of 100 (10x10). A 100-fold increase in  power 

 is 20dB.

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