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[TowerTalk] Noise and WANs

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Subject: [TowerTalk] Noise and WANs
From: (Ford Peterson)
Date: Tue, 18 Sep 2001 10:38:08 -0500
On Monday, I wrote:

"Monday night I am sponsoring a picnic for the local ham radio club.  One of
the members works for the WAN company (ISP) and is bringing his mobile 2.4
GHz Wide Area Network setup in his pickup truck to demonstrate 500MB/Sec WWW
interconnect from the vehicle."

Well they were here and did a demo.  It is not 500MB!  I witnessed a 15MB
download that completed at 43K/sec, which suggests 344K Bits.  It may cook
up to 500KBits/sec on a good path.

They were using WANs called "Breeze" units.  Go to ebay and search on Breeze
and you will see many units sold every day.

I was completely unable to detect any signals on my HP141T/8555/8552
analyser.  Unless you put these animals on the bench and control the RF
path, I doubt you would ever see the signals.  The unit is 50mW spread
spectrum (both pseudo random and hopping according to the tech that was
here).  A 2 foot dish was used to complete the 3.5 mile link.  He could view
the received and transmitted signal strength using software that accesses
the repeater node.  The signals were apparently -72dbm at the receive site
and -75 dbm on our end.

I could detect nothing on any 2m or 70cm or my HF gear.  This is hardly a
good test fixture.  I am in a rural area located 3 miles from any
civilization.  These broadband devices may work fine in a quiet environment
but I wonder what kind of mixing products are produced with other signals

They had been doing modifications to the network yesterday and at 6PM, the
Hutchinson repeater was falsing about 1 time every 3 - 5 seconds for almost
an hour.  The McLeod County Sheriffs department has been unable to use
handheld radios because of some digital garbage taking out their channel.  I
have heard it and it sounds like 9600 baud stuff.  It appears every 50kHz
for about 1 MHz centered around 154,900.  Each burst lasts abou1 second and
it repeats every 1.5 to 3 seconds.  Very strange.

Without getting a system into the lab, equipped with an analyser much more
sophisticated than mine, I doubt you will ever be able to even view the
signals.  If these are the cause of local RFI, it would have to be shown at
the site, not through an experiment like the one I conducted last night.
These high gain dish antennas are very narrow-possibly 5 degrees or less.
Without being in the direct path of the beam, you would never even see the
signals on the analyser.

Thanks for all the input and suggestions.  Ed Hare (ARRL RFI guy) was quite
helpful.  Unfortunately, I learned nothing last night.


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