[Cu-wireless] Summary of antenna test results

[David Young]

Here are the numbers I wrote down from the collective memory after
we finished.

                                       Distance
                               |  580m               1.3km
-------------------------------+------------------------------
Antenna  NCSA Helical          |  17dB               16-17dB
         Pringles              |  25dB               20/25dB
         Peter&Dave's Helical  |  15-20dB
         Parabolic             |  50dB

I had a hunch that we'd get better reception with all antennas at a height
off the ground.  I only tried the Pringles. At 1.3km, we got 25dB when
I stood on top of the van with the Pringles can antenna, 20dB with the
same antenna when I stood on the ground beside the van. I suspect that
the ground plane of the earth affects reception (there appears to be a
lot of discussion of some such phenomenon in the ARRL Antenna Handbook),
but there's no telling. It was not a very scientific test, climbing on
the roof of the van.

Dave

On Mon, Nov 12, 2001 at 03:00:38PM -0600, Peter Folk wrote:
> We had two each of four types of antennae in addition to the built-
> in ones:  pringles-can-based, 90cm helical (made by myself and Dave
> Young), 55cm helical (made by NCSA), and parabolic grid antennae
> (manufactured commercially).  The pringles-can took about $10 and
> 1/2 hour to make, the helical cost about $15 and took 4 hours to
> make.  The parabolic grid cost about $59.
> 
> The way strength is measured is signal-to-noise ratio, in decibels
> (for signal strength S and noise level N, SNR = 10*log(S/N)).  That
> means a change of ~3 (actually 10*log(2)) indicates a 100% change
> in actual signal strength.  Anything above about 2db will provide a
> connection, but below about 12db it will be slower, and below 15db
> it seems pretty flaky.  Someone walking in the path of the signal
> near the antenna causes about a 3db drop.
> 
> The best, by far, was the parabolic grid (looks like a rectangular
> 2'x3' sattelite dish made of wire).  At a distance of 600m, we got
> slightly less than 50db---a very strong signal.  With the normal
> antenna, you get that at 10-15'.  But the pringles can was amazing!
> At 1300m, we got about 25db, putting it quite a better than the hel-
> icals, and definitely good for a multi-mile link.  The helicals put
> in a rather pitiful showing; NCSA's provided 15-18db and ours pro-
> vided 17-20db at 600 meters.  This may be due to our rather crude
> aiming methods---we should give them at least one more chance.
> 
> The grids were impressive, but by dollar and minute spent the
> pringles cans were spectacular.  Our next goal is to try to find
> the maximum distance we can get, which requires finding the long-
> est line of sight we can.
> 
> 
> I bought the parabolic grids from <http://www.electro-comm.com/>
> (download the PDF catalog).  If they want to charge you the MSRP, let
> me know and I'll sell it to you at dealer cost.  Our pringles cans
> were based on <http://www.oreillynet.com/cs/weblog/view/wlg/448>.  You
> can get most of non-antenna-specific the hardware from DoIt in down-
> town Champaign (w/ a 15% discount if you're a student), but I have
> plenty of extra copper tubing, a few extra all-thread pieces, and a
> tubing cutter I can lend, so don't get those =)
> 
> Pete
> p.s. Dave has more details wrt the performance numbers if people want
> them.
> 
> 
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-- 
David Young                   On the Job Consulting
dyoung at onthejob.net     Urbana, IL * (217) 278-3933