[amsat-bb] Re: S band interference solution

Nate Duehr nate at natetech.com
Thu Oct 5 09:39:00 PDT 2006

John Champa wrote:
> I really do get bored reading about all these threats to Mode S from WiFi, 
> etc.
> NOT!
> These are 100 mW devices...maximum!  That means they have to be relatively
> close to your QTH for you to hear them.

I've got one here that will happily do 250mW all day long... not that I 
run it that way.  All it took was some alternate firmware to bypass the 
normal firmware's limits.  However, 28mW is plenty to cover my house.

> 1. Pick up your old laptop, or borrow one.
> 2. Plug in a Linksys wireless PC card from Radio Shack.
> 3. Download the free NetStumbler shareware.
> 4. Find the source of the Wifi QRM.

4a. Explain to the nice Sheriff's deputy why you're walking around the 
neighborhood and into neighbor's yards with a laptop.

4b. Call your wife and ask her to come pick you up from jail.  Explain 
to wife on the way home that you're not a "terrorist" as the Sheriff's 
summons for your later court date indicates.

> 5. Knock on his door and ask him to change his AP to a channel 7 - 11 
> (outside the Ham Band)

5a. Listen to 1/2 hour tirade about how this guy bought the thing at the 
local Best Buy and they never told him about the ham band, and how he 
saw a UFO fly past your tower one night.

5b. Another 15-30 minutes talking about "What's that tower for, anyway?"

5c. Spent an hour in his basement with him, helping him click on simple 
web interfaces after you reset his router to a default password and have 
to set it up from scratch because he's forgotten his password... which 
turns out to be "beerrules" and is found on a Post-It note on the bottom 
of the router AFTER you've already reset it to factory defaults.

> 6.  Reason: He's interfering with a licensed radio service  (be nice!).

6a. If you were dumb enough to point this out to Joe Sixpack, expect 
another 1/2 hour explaining Part 15.  If you're lucky, Joe will offer 
you a beer at this point.

6b. If you're *REAL* lucky he might be interested in ham radio.  (This 
is about the only good that can come of this.)  Spend another hour today 
and many more Elmering.  (Yay!)

> 7. Return to your radio room and operate Mode S until LOS.

7a. The satellite passed over long ago and it's time for bed anyway.

7b. Alternatively Joe may have you "help me fix my computer while you're 
here", and you'll spend at least one weekend a month at the neighbor's 
house or another neighbor's house (once word gets around) dealing with 
their computer problems, virii, and other technical duties now that 
you're the "friendly computer guy in the big white house over there!"

> This is child's play guys!  These are consumer grade wireless devices, not 
> super computers.
> Fixing such local QRM issues is easier than solving the old fashioned TVI 
> problems.

No.  The average public at least understood how their TV worked, or at 
least how to adjust a pair of rabbit ears.  WiFi is "deep voodoo black 
magic" to the vast majority of the population in most neighborhoods 
today.  They think they paid for a system that works perfectly, 100% of 
the time and they have their own "channel".  Some have heard enough to 
turn on the WEP encryption in their routers (crackable, easily).

(Heck I've seen Engineers where I work stare and boggle at a simple 
Radio Frequency Spectrum chart, like the one you can download and print 
out from the NTIA.  They always ask: "So where's my cell phone on here?")

> The most troublesome devices I have found , even to WiFi, are 2.4 GHz 
> cordless phones.
> In that case the only solution I have found is to go next door and offer to 
> buy him a replacement
> cordless phone of any type he would like EXCEPT one on 2.4 GHz.  That is a 
> cheap
> solution.  They're usually not more than $79.95 while you probably have 
> multiple Ks of $
> invested in your satellite ground station.

Yeah - move 'em up to 5.8 GHz!  Oh... wait...

Maybe down to 900 MHz... Oh, oops... some of us are there too... hmmmm...

> For a bunch of supposedly sophisticated wireless guys, you sure don't know 
> beans about
> consumer grade wireless devices.  That includes our wonderfully dedicated 
> but pessimistic AMSAT satellite engineers!

I know plenty about them and know I'll end up the neighborhood tech 
support guy for them if I even THINK about talking to a neighbor about 
them.  That and their utterly broken Windows 98 machines they THINK they 
need.  Thanks to mass marketing... "Your child will be smarter if you 
buy them our operating system!"  (No, it has nothing to do with genetics 
or the fact there isn't a single book in the house!)

> Now get on with the work, and get those birds into orbit!  (HI).

Ditto on that, at least!  :-)

> Vy 73,
> John Champa, K8OCL
> AMSAT Life Member 1069

Nate WY0X

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