[n7cl@toontown.mmsi.com: Re: [TowerTalk] A Question of GAIN]

[force12@interserv.com]

GOod morning.

Spacial and polarity diversity are both useful. Mr previous company was focused 
on in-building communications utilizing 2.4 and 5.8 GHz. Besides providing the 
basic radio architecture, I also provided the antenna(s) that mitigated 
multipath (fading). The practical situation in this case is that communicating 
inside a building has the typical condition that the path from the handheld unit 
to the base is always obstructed; therefore, multipath is not only a problem, 
but it is also the only way to get from point A to point B. We were able to 
measure the distance between nulls, as well as the frequency difference between 
nulls. This underscored that nulls to not occur simulataneously on all 
frequencies, nor in all physical locations. Frequency hopping is obviously one 
solution and was utilized, as well as other spread techniques. My work related 
to the antenna systems. A very short summary is that the implemented solution 
was the use of an equal-component diversity antenna on the handheld (moving) 
unit and spacial diversity on the fixed unit. The main issue was to avoid the 
-20dB nulls.

The reference antenna used was a Lindenblad, which is circularly polarized and 
omnidirectional. It was very effective, but difficult to build. The equal 
component diversity antennas that were eventually implemented were a half-size 
loop and one nick-named the "inverted U". If built properly, they both had equal 
components of horizontal and vertical (linear) polarization. The operational 
result was that the -20dB nulls were not experienced.

My notes are buried somewhere since we moved to this new location; otherwise, I 
could provide additional information about the physical distance between the 
nulls. From memory, effective distances between antennas for spacial diversity 
was much less than anticipated.

Hope this is useful.



Have a great day & 73,
                Tom Schiller, N6BT
		President, Force 12, Inc.
			Amateur Antennas, Commercial Towers & Antennas
		P.O. Box 1349 Paso Robles, CA  93447
		Phone: 805.227.1680   FAX 805.227.1684
		Web Site: http://www.QTH.com/force12






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