[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: No Stupid Questions, right? (focal point)



Hi Fred

Can I ask a question relative to the phase center subject ?     When
phase center is calculated , is it not calculated for a specific
frequency?     Case in question is where a log periodic feed antenna is
used ,  the phase center moves with frequency .    Or can a log feed be
made for a single frequency.       And how about a similar case where a
wide band helix feed where a dual coaxial, helix feed does not have to
move with frequency .     I have been wanting to try the dual coaxial ,
same hand , axial mono filar helix feed for 1.2 and 5.6 up links.

Thanks

Joe  K0VTY
=======================================
On Wed, 09 May 2001 14:17:45 -0000 "Frederick M. Spinner"
<fspinner@hotmail.com> writes:
> Phase center refers to the "point" at which maximum signal is
> radiated in the near-field of a feed/antenna (highest current 
> density).  
> Some of the more mathematical friends of Maxwell around
> here will say this is "oversimplified" but this is the point when
> dealing with dish feeds/dishes.
> 
> Focal point, of course, is the optical focal point of an object, 
> usually a 
> parabola (but a sphere has a focal "line" so other geometric objects 
> can be 
> used).
> 
> The idea is:  Put the phase center at the focal point for max gain.
> 
> This can be done by calculation, or even easier still, slide the
> feed back and forth for maximum signal while listening to the bird.
> 
> Fred W0FMS
> 
> 
> 
> >From: "Howard Long" <howard@howardlong.com>
> >To: "Rich Dailey, KA8OKH" <okh.npi@gte.net>, <amsat-bb@AMSAT.Org>
> >Subject: RE: [amsat-bb] No Stupid Questions, right? (focal point)
> >Date: Wed, 9 May 2001 08:03:02 +0100
> >
> >Rich
> >
> > > Ok then... what's the difference between "phase center"
> > > and "focal point"?
> >
> >For us Microwave Newbies all this info is of interest.
> >
> >I have no idea, even when you know the phase center, which bit of 
> the 
> >coffee
> >can / helix / yagi / log periodic / trapezoid should be putting 
> there
> >anyway.
> >
> >Any info greatly apprciated here too!
> >
> >73 Howard G6LVB
> >
> >----
> >Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> >To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> 
> _________________________________________________________________
> Get your FREE download of MSN Explorer at http://explorer.msn.com
> 
> ----
> Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> 
________________________________________________________________
GET INTERNET ACCESS FROM JUNO!
Juno offers FREE or PREMIUM Internet access for less!
Join Juno today!  For your FREE software, visit:
http://dl.www.juno.com/get/tagj.
----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home