[TowerTalk] UHF aircraft antenna

[n0tt1 at juno.com]

OK, thanks Jim.  I made up a drawing, just for talking
purposes.  Just guessing here...Does THIS represent the "single port"
type
of glideslpoe antenna, and how it is matched to say, a 50-ohm coax?
All input welcome!

http://tinypic.com/view.php?pic=8yercz&s=8#.VKWBBIF_vSs

Thanks,
Charlie, N0TT

On Wed, 31 Dec 2014 22:50:47 -0800 Jim Lux <jimlux at earthlink.net> writes:
> On 12/31/14 8:34 PM, n0tt1 at juno.com wrote:
> > Guys, just curious....what's "inside" one of these aircraft
> > glide slope antennas and how are they matched
> > to say, a 50-ohm coax.
> 
> Basically half of a folded dipole: a folded monopole. Narrow band 
> matching: Glide slope is a bit above 300 MHz with a span of about 5 
> MHz, 
> so about 1-2% BW
> 
> http://en.wikipedia.org/wiki/Instrument_landing_system
> 
>   One ham has one of these
> > mounted on his car and he uses it for RFI
> > location....the one with the "tap" on the upside-down U.
> > Kinda looks like a dual loop antenna.
> >
> > There is another antenna with a single loop in
> > the upper right of the screen...looks like an insulator
> > in the middle of the loop.
> 
> Aerodynamic design, basic conservativeness in the aviation biz, 
> avoiding 
> patents from other companies. There's only so many ways to make an 
> omni 
> 300 MHz antenna.
> Actually, you might want a pattern that's sort of fore/aft, since 
> you 
> generally don't start looking at the GS until you're on final and 
> lined 
> up with the localizer.
> 
> 
> 
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