[Ham-Computers] RE: ADVICE - wireless

[Hsu, Aaron (NBC Universal)]

Yep, good ol' "fundamental overload".  Doesn't matter what freq you're
using, when a receiving device is near a radiating device, it's possible
that something in the receiving device will be affected (be it the front end
or even some relatively minor circuit "downstream".  Ever put your 500mW
cell phone near a monitor and notice the wavy lines?  How about putting that
cell phone near some powered computer speakers...ever hear that buzz or
chirp-chirp-chirp sound?  Yep, fundamental overload.  Even simple devices
like a 12v linear power supply can be affected...the Astron RS-35 is known
to sometimes "act funny" in the presence of a strong RF field.

The best way to combat/prevent "FO" is RF shielding or filtering.  Bypass
caps are cheap and effective.  But, at some point in history, some num-skull
penny counting accountant said "if we eliminate this one cap in this
circuit, the unit will still work and we'll save thousands of dollars.
Hmmm, do you really need this bypass cap?  We'll save even more money if we
remove it too".  A few years ago, if you looked at some circuit boards, you
would've seen solder pads where a bypass cap should have been (component
removed after design to save money).  Now-a-days, you won't even see a spot
for a bypass cap as that's valuable real estate for other "useful" devices.

Another problem...802.11b/g use the 2.4GHz ISM band.  This band is also used
by cordless phones, medical devices, HAMs, experimenters, etc.  It's
basically license free at certain power levels.  When I use my 2.4GHz
cordless phone, my wirless data rates drop to almost nil.  I've mitigated
things somewhat by using smaller packet sizes and, luckily, I don't use the
wireless that often.  For me, moving back to a 900MHz DSS phone would help
greatly, but all the 900MHz cordless phone out there now just royally suck
(in both build quality and features).

Anyways, I digress.  Rolly, please realize that the problems you're
experiencing with your wireless devices have really nothing to do with your
HAM hobby.   By eliminating proper RF/EMI filtering to cut costs, the
manufacturers of the various wireless equipment are to blame (and the
consumer suffers...especially we HAMs with non-technical neighbors!)

73,

  - Aaron Hsu, NN6O



-----Original Message-----
From: Rolly (W7DGX) & Sandra Goodspeed [mailto:rollyg at earthlink.net]
Sent: Sunday, August 15, 2004 5:05 AM
To: Computers (or other) used for amateur radio, communications, or
experimenting
Subject: Re: [Ham-Computers] ADVICE - wireless


I am curious about wireless LAN.

I have experimented with wireless keyboards and mouse. Both worked fine
until I transmitted. Somewhere in the 30 to 50 watt range these wireless
devices would quit entirely or become intermittent. At my normal 90 watt
level the wireless keyboard and mouse were inoperative. I also have problems
with the indoor/outdoor thermometers. These devices operate around 432 MHz.

Because of this, I question all wireless devices around amateur radio,
especially inexpensive ones. I have found the good (not cheap) 900 MHz and
above wireless phones to be relatively immune. Sometimes running near legal
limit power, there will be a scratchiness on voice peaks.

The exception to this is 75 meter operation. There I have a phone line
running between the house and the garage that is about 35 feet long, and
approximately 12 feet in the air. My 75 meter dipole runs almost parallel
with that phone line and is only 22 feet high. Thus high power 75 meter
operation kills the phone regardless if a cordless phone is used or not.

As soon as I am well enough, I expect to bury that line. Hopefully that will
resolve that problem. If not,  I may remove the line entirely to the garage
and put a 900 MHz or above wireless extension in the garage.

  Rolly W7DGX