Subject: [NEXTEL-1] Antenna theory

From: [email-masked]
Date: Wed, 02 Jul 2003 23:04:38 -0400

-------- Original Message --------
From: Mark Krotz <[email-masked]>
Subject: Antenna theory

Can anyone point me to a reference, or comment on the following:

In the example of an exposed dipole design antenna (ie, DB222, DB224), 
how does the spacing between bays affect the gain of the antenna? 
Probably best to think in terms of a 2 bay antenna.

I know that there is an optimum max gain spacing, and increasing or 
decreasing the spacing from that lowers the gain.. but interested in a 
deeper look at it.

Also, interested in the affect on gain, tilt, etc if the bays are fed 
out of phase, and same question for "corporate feed" (all bays receive 
the same power) vs. series fed (power varies between bays)?

M

------------------------ Yahoo! Groups Sponsor ---------------------~-->
Get A Free Psychic Reading! Your Online Answer To Life's Important Questions.
http://us.click.yahoo.com/Lj3uPC/Me7FAA/ySSFAA/61FxlB/TM
---------------------------------------------------------------------~->

Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/

---

From: [email-masked]
Date: Thu, 03 Jul 2003 02:45:40 -0400

------- Original Message --------
From: Jack Daniel <[email-masked]>
Subject: Re: Antenna theory

Interesting. We have taken different forks in the same road. ha ha.

I agree 100% with your assesment that using a circular polarized TX and
antenna and a linear RX antenna will result in some less-than-optimum
reception in any case. 

My point was when the RX antenna is also circular polarized in the same
rotational direction as the transmit antenna multipath (i.e reflections)
will reverse rotation and be attenuated by the rotational selectivity of
the receiving antenna. Perhaps easiest way to visualize this is a
reflected signal immediatly behind the receiving antenna. If the
direct/desired signal is CCW the reflected signal will be CW relative to
the recivunbg antenna. Since this scenario uses selectivity instead if
cancellation mechanisms, I suspect the desired signal level would always
be greater than in the cricular-to-linear set-up.

This is an interesting discussion because we are using different
mechanisms to resolve the same problem. Now I wonder which would be
superior in differnt applications? 

Instinct tells me your linear antenna (mobile whip) would be most
practical on a moving receiver and a circular polarized might be better
for a stationary receiver. But I'm not sure.

Hmmmmmmm.... gotta dust off some books.....

Jack Daniel
(I WILL trim, I WILL trim,..)
===================================================

---

From: [email-masked]
Date: Thu, 03 Jul 2003 15:53:27 -0400

------- Original Message --------
From: Jack Daniel <[email-masked]>
Subject: Re: Antenna theory

Dave,
As I remember vaguely this worked well in point-to-point video links to
eliminate 'ghosts'. Since the picture mod is AM, multipath manifests
itself as weaker, off-centered images. With FM audio and limiting, the
'capture effect' made the results even more dramatic. The 6 dB C:C+I
capture ratio fell easily within the polarized:non-polarized
selectivity of the antenna. Maybe some STL engineer can jump in here.

The neat thing is circular polarization is binary (cw or ccw). I can't
imagine anything in between as a result of multipath reflections, but
some complex multi-source analysis might prove otherwise. (As an aside,
I don't think we give capture effect the credit it deserves.)

In the early days of CB, there were several 'unofficial' forays into
such experiments and (as you say) circ-to-circ was tested on mobiles in
urban canyons between large buildings and it worked but was a large and
ugly mobile install. Three others that come to mind are;

Low band couplers to' load' a drilling rig derrick leg and make it an
antenna. Later tested as a way to use tower guy wires as antennas below
50 MHz. (tired it a couple of times myself at remote sites on our 35.06
company wide channel - yes, we had 'interoperability' back then. ha ha). 

Concealed 'skin effect' mobile antennas where the outer surface of a
trunk lid was loaded as an antenna.

'Skip' cancellation using angle of arrival between line-of-sight and
over-the-horizon to differentiate carrier only and carrier plus skip.
Phase cancellation only (amplitude cancellation required too much
equipment at the time).

Ahhh. Imagine dabbling in empirical whimsy where no idea was invalid
unless proven impractical or impossible. What happened to those days? 

(Don't answer that question, it is depressing)

HAPPY 4th OF JULY 

Jack Daniel
===============================

Maples, Dave wrote:
> 
> Jack: Your analysis seems to hang together well, although I have never
> heard of a circ-to-circ system being installed to deal with
> multipath.  It's an interesting concept.  Wonder if it might be used
> (or is already being used, probably) to improve reliability of
> point-to-point shots in urban areas or over long paths?
> 
> Dave Maples
>

------------------------ Yahoo! Groups Sponsor ---------------------~-->
Save up to 80% on top-quality inkjet cartridges and get your order fast!
FREE shipping on orders $50 or more to the US & Canada. Shop at Myinks.com!
http://www.c1tracking.com/l.asp?cid=5511
http://us.click.yahoo.com/v2G7ND/KfUGAA/ySSFAA/61FxlB/TM
---------------------------------------------------------------------~->

---

From: Anderson John-P29444 <[email-masked]>
Date: Thu, 3 Jul 2003 13:07:16 -0700

Very much so, and no, steering is not required due to polarization.  GPS, for instance, is right hand circular and used on aircraft, so very fast, no steering.  I have personally designed a circular polarized phased array mounted on an aircraft that was an electronically steered beam and there is no connection between steering and polarization (independent variables).

-----Original Message-----
From: Jack Daniel [mailto:[email-masked]]
Sent: Thursday, July 03, 2003 12:42 PM
To: [email-masked]
Subject: Re: [NEXTEL-1] Re: Antenna theory

Thanks John.

Are these used while the paltform is in motion?

If so, is antenna steering required. 

Jack Daniel

Anderson John-P29444 wrote:
> 
> The Department of Defense uses circularly polarized systems on all
> kinds of mobile platforms.  The basic tradeoff is robust performance
> over all conditions vs. peak gain under certain conditions.  Linearly
> polarized systems are more an artifact of history than anything else.
> Just like 50 ohm cable.
> 
>      -----Original Message-----
>      From: [email-masked] [mailto:[email-masked]]
>      Sent: Wednesday, July 02, 2003 11:46 PM
>      To: [email-masked]
>      Subject: [NEXTEL-1] Re: Antenna theory
> 
>      Your use of Yahoo! Groups is subject to the Yahoo! Terms of
>      Service.
> 
>                    Yahoo! Groups Sponsor
>                        ADVERTISEMENT
>                         [click here]
> 
> 
> Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.

Yahoo! Groups Sponsor	
 <http://rd.yahoo.com/M=249982.3512844.4795476.1261774/D=egroupweb/S=1707367802:HM/A=1524963/R=0/SIG=12o72ctft/*http://hits.411web.com/cgi-bin/autoredir?camp=556&lineid=3512844&prop=egroupweb&pos=HM> 	
  <http://us.adserver.yahoo.com/l?M=249982.3512844.4795476.1261774/D=egroupmail/S=:HM/A=1524963/rand=296961461> 	

Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service <http://docs.yahoo.com/info/terms/> .