[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

RE: 2.4GHz QRM



I would comment that Part 15 consumer devices could be a real problem for
435 to 438 MHz Satellite reception and 432 weak signal work, particularly
those Part 15 devices that operate around 433.9 MHz. (I wish someone can
tell why they picked that frequency when Part 15 says they can operate
almost anywhere below 1000 MHZ. Check out the ARRL web site at
http://www.arrl.org/tis/info/part15.html#Technical for more details.)

Case in point.

I always wanted one of those "neat" wireless weather stations. I just can't
get enough weather statistics!

Last Christmas my wife filled my wishes. It came with remote temperature
sensors, rain gauge and an anemometer. It operates in the 433.5 to 434.5
band, more specifically right around 433.9 MHz. The best I can interpret is
that they run about -10dbm output and operates under Part 15.231 for
periodic intentional emitters.

Now, silly me, I knew all this and went ahead and mounted the anemometer at
the best location on it's own 20 foot mast, to get it in clear air. That put
it about 20 feet distance from my 435MHz antenna and LNA (0.4 dB NF). Well
golly, every time the anemometer pinged its signal back to the base unit -
every 12 seconds - reception at 435.3 was momentarily blanked by overloading
the LNA. Very annoying!! Now there is no practical way to filter before the
LNA for a signal only 1.4 MHz away and running -10dBm.

By the way, the temperature and rain gauge sensors weren't a problem since
they were at least 100 feet from the 435 MHz gear and ping about every 45
seconds to a minute, but they too can cause LNA de-sense if mounted too
close to your LNA.

Solution - the anemometer was promptly removed. Problem gone!

The point is that we need to understand that there are many emitters out
there competing with us and our relatively weak satellite signals, and I
image it will only get worse in the future.

Regards...Bill - N6GHz


-----Original Message-----
From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
Behalf Of Emily Clarke
Sent: Tuesday, August 01, 2006 10:14 PM
To: Tony Langdon (ATC); 'amsat-bb@amsat.org'
Subject: RE: [amsat-bb] 2.4GHz QRM


Hi Tony,

But how much is it a problem in (say) 435-437?  434 is not an amateur
satellite allocation - it may be for terrestrial use, but it
shouldn't cause us to roll over and play dead in the satellite
allocation unless there is a real threat.

My other concern is that if we publicly acknowledge that the band is
a wasteland that it most certainly will be, because the message is we
don't care about it.

73,

Emily



At 09:42 PM 8/1/2006, Tony Langdon (ATC) wrote:
> > I'm a little concerned about the message here - are you saying that
> > RFICs in 434 MHz will encroach on our allocation in 435-437?  These
> > are minuscule power devices (since, for example, sitting on the
> > freeway I don't want to get warnings about the tire pressure of
> > another Volvo 1/2 mile away.) So before I get all bent out of shape
> > by this can you provide some credible data or (ugh) statistics that
> > it will have any real impact in the next 20 years?
>
>I suspect these will cause you guys few issues.  Over here, 434 MHz devices
>are a real problem, but it's not the door bells, garage door openers or the
>vehicle remotes that are causing the problems, but it's the hiher powered
>high duty cycle devices (they're allowed up to 25 mW EIRP) that cause all
of
>the problems, cordless headphones and industrial crane controllers being
the
>worst offenders.  All made worse by the fact that this part of the spectrum
>overlaps most of our repeater inputs. :-(
>----
>Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
>Not an AMSAT member? Join now to support the amateur satellite program!
>To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
----
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
Not an AMSAT member? Join now to support the amateur satellite program!
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
----
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
Not an AMSAT member? Join now to support the amateur satellite program!
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home