Archived from groups: alt.internet.wireless (
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In article <vtvcf0t8k1lun400h87jpennaktfi0njbd@4ax.com>,
jeffl@comix.santa-cruz.ca.us says...
Top Posted - Thanks - Nothing new to add.
> On Thu, 15 Jul 2004 08:11:47 GMT, John S <none@none.none> wrote:
>
> >I have used a ton of the classic Orinocos but never have taken one apart
> >so your picture in your other response was interesting. I thought they
> >used the dual antenna diversity scheme too but maybe I am wrong.
>
> Dunno. I only take apart the radios that do NOT work well, so I've
> never bothered to disassemble an Orinoco radio. If there's a
> diversity RF switch, it's on the bottom which is not in the photo. If
> I need entertainment, I'll tear one apart.
>
http://www.geocities.com/lincomatic/orinocoant.html
> However, looking at the horizontal antenna pattern, with it's pair of
> symmetrical deep nulls, I would guess(tm) that the two PIFA are being
> run through some kind of combiner. Difficult to tell.
>
http://www.proxim.com/support/all/orinoco/technotes/antenna_patterns/classic_gold_pc_card.doc
>
> >I still
> >do not understand the circuit though.
>
> Which circuit? The WPC11 schematic is fairly simple if you totally
> ignore the use of improper schematic symbols. My guess(tm) is that
> it's simply a SPDT (or dual SPST) PIN diode switch. The real question
> is what algorithm is used to switch antennas. My guess(tm) is that if
> the S/N ratio drops below some level, it switches antennas in the hope
> that reception on the other antenna will be better. I've seen some
> access points, with diversity antenna systems, that use diversity only
> on receive and always transmit into one antenna. That drove me nuts
> for about a week trying to setup an access point with one antenna for
> outdoors and the other for indoors. I could make one or the other
> work, but not both. I'm not convinced that diversity actually works
> well enough to justify the efforts.
>
> >And I do not understand how the
> >external antenna can be "paralleled" without screwing up the
> >VSWR/Pattern etc.
>
> If both antennas can see each other, then running the antennas through
> a combiner (resistive, Wilkinson, active mixer, etc) will result in a
> conglomerated pattern full of nulls, peaks, and problems. However, if
> the antennas are sufficiently separated so that both antennas do not
> simultaneous hear the same signals, then the pattern will be the same
> as a single antenna. However pattern mangling is not the problem.
> It's that two physically diverse antennas are most likely to pickup
> additional noise sources without much improvement in signal reception.
> The only way around that is to switch antennas as in the various
> diversity schemes.
>
> >You sound like an RF circuit design engineer too.
>
> Sorta. I did that full time for about 15 years. These days, I do
> computah repair/consulting and RF consulting. I try to keep up to
> date on both, but it's rough. Most of the stuff I post in the various
> newsgroups and mailing list involve no more than the fundamentals.
>
> >I hated antenna
> >design since the final result was hard to test without a chamber.
>
> Antenna design is little better than magic. I've verified some of my
> designs and was amazed at the discrepancies between theory and
> reality. At 2.4GHz, a relatively small chamber will do the trick.
>
> >And
> >back when we used NEC simulator the input modeling was a hassle. Hope it
> >is easier to use now.
>
> Oh yes. Things are much easier these days. User hostile NEC2 and
> NEC4 Fortran based calculation engines are now the back end
> calculators with various user friendlish programs at the front end. I
> still recall discussing antenna modeling with one of the luminaries of
> NEC modeling at a meeting. He couldn't understand why anyone would
> need a 3D visualization of the pattern or a near field pattern. That
> was 10 years ago and much has changed since.
>
http://www.nec2.org
>
http://www.qsl.net/wb6tpu/swindex.html
>
http://www.gweep.ca/mailman/listinfo.cgi/nec-list
> If you wanna play, I suggest the freeware 4NEC2 software or the EZNEC
> demo. Here's some sample output for a 1lb coffee can:
>
http://www.LearnByDestroying.com/antennas/coffee2400/index.html
>
> These daze, everything is first modeled on the the computah. It's too
> difficult to do cut-n-try design work. I was quite successful with
> cut-n-try 30 years ago, but with todays high density circuits, the
> very concept of a "breadboard" is dead issue. If it doesn't first
> work on the computah, it probably won't work when it's built.
>
>
>
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