[lug] hardware question

Mon Nov 9 11:06:34 MST 2009

Cool story Frank. Hunting down RF interference is a highly specialized,
but fun, thing to do.  

Some of the newer crop of Spectrum Analyzers are amazing.  They can take
a "known frequencies" list (usually the FCC licensing database and with
the right clearances the NTIA/Federal/Military data), correlate the
unit's location via GPS to the transmitters, and calculate the mixes
expected from the licensed transmitters, including the signal strengths
expected.  Multiple spec-an devices in the box, all computer controlled.
Then they start hunting for the unlicensed "stuff"... pretty amazing
gadgets.

Meanwhile, I'm using old (meaning, 80's vintage) gear for most things I
do, or borrowing from friends in the commercial world.  Those receivers
aren't very sensitive... but they were top of the line test gear in
their day.

It's amazing how little thought we give to all the hard-workin' folks
out there still in the trenches doing RF work.  We all carry "radios"
these days.  Usually more than one.  Some of the coolest RF tech in the
world comes right outta Boulder there at Qualcomm.  Serious brains
there.

--
  Nate Duehr
  nate at natetech.com

On Fri, 06 Nov 2009 21:34 -0700, "F.L. Whiteley"
<techzone at greeleynet.com> wrote:
> I've tracked down frequency harmonics that affected electronics also,
> including translation frequencies within some devices that may not be
> filtered at that level when the operating bandwidths were filtered.
> I've seen some interfering harmonic signals travel as ground waves also.
> 
> We also had some corrosion on an element at one site and the wave guide
> was dumping into the antenna structure.  Every nut, bolt and strut was
> cutting frequencies and we were blanking UHF and VHF in a 150 mile
> radius with brief transmissions at 10KW.  Played havoc with air traffic
> control (in another country).  One broadcast was hourly at a specific
> minute, which is how it was finally tracked to our site.
> 
> Good RF spectrum analyzer should show if anything spurious is happening.
> 
> Frank Whiteley
> (USAF-ret)
> 
> > -----Original Message-----
> > From: lug-bounces at lug.boulder.co.us 
> > [mailto:lug-bounces at lug.boulder.co.us] On Behalf Of Nate Duehr
> > Sent: Friday, November 06, 2009 17:12
> > To: Boulder (Colorado) Linux Users Group -- General Mailing List
> > Subject: Re: [lug] hardware question
> > 
> > 
> > And according to Dan's corollary, as soon as I walk into your office
> > with an RF spectrum analyzer to find and kill the culprit, your tablet
> > would start working perfectly.  :-)
> > 
> > (In other words, it IS possible to measure and "see" RF interference
> > sources and coordinate frequency use, but in an environment where
> > multiple products are all using the same spectrum, anything goes...)
> > 
> > What's weird here in your example (but not unheard of) is the Wacom
> > isn't wireless, right?  It's wired?  Sounds like some SERIOUS 
> > heavy-duty
> > RF fields from that radio station are getting rectified in 
> > the wires and
> > some engineer saved $0.30 not putting RF bypass capacitors on the PC's
> > serial/parallel port.  
> > 
> > (That's an assumption... if it's USB... whoo boy do you have 
> > a lot of RF
> > floating around!!)  
> > 
> > :-)
> > 
> > --
> >   Nate Duehr
> >   nate at natetech.com
> > 
> > On Fri, 06 Nov 2009 14:20 -0700, "Chris Riddoch" <riddochc at gmail.com>
> > wrote:
> > > On Thu, Nov 5, 2009 at 9:22 AM, Jack Swope <jack.swope at comcast.net>
> > > wrote:
> > > > Magic is key, a certain people have the right aura.  As a 
> > system and
> > > > desktop admin, I have fixed more email, web, and 
> > application problems
> > > > simply by walking into the affected person's office ;-).
> > > 
> > > Here's a rather frustrating one that this makes me think of...
> > > 
> > > I have a wacom tablet, which I use all the time.  When I 
> > took it with
> > > me to a job I once had, it became unusable - the pointer was jumping
> > > all over the place, only bearing a vague resemblance to where the
> > > stylus was pointing.  At home, it worked fine.  At every 
> > coffee shop,
> > > library, or friends' place I've taken my laptop to, it works fine.
> > > Just at that one office, it wouldn't work.
> > > 
> > > Probably not coincidentally, coworkers couldn't use 
> > wireless mice, and
> > > the 802.11 was slow and unreliable.
> > > 
> > > I blame it on the radio station tower planted a hundred 
> > feet away from
> > > the office.
> > > 
> > > -- 
> > > Chris Riddoch
> > > _______________________________________________
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