postal97321 wrote:

Sunday, October 17, 2004
Last modified Saturday, October 16, 2004 10:40 PM PDT


Ryan Gardner/Gazette-Times
Chris van Rossman's television sent out a distress signal that was
picked up by an orbiting satellite.


"All electronic equipment creates a frequency called a tempest," he
said. "Sometimes these frequencies emit low-level signals that are
close to the 121.5 MHz signal."

Mandrell has heard of this sort of thing happening with customized
computer gear. Sometimes CAP equipment will pick up these signals, he
said, but they are usually weak enough to ignore.



What exactly are these search and rescue people listening for? Wouldn't
an emergency beacon be sending some kind of intelligent signal, like SOS
in morse code, or some kind of RTTY? At the very least, a certain kind
of modulated tone. It seems to me that if they're going to chase after
every spurious signal that pops up on 121.5, no matter what it sounds
like, that's a recipe for failure. No wonder 90% of their hits are
false positives.

Tony Calguire wrote:
What exactly are these search and rescue people listening for? Wouldn't
an emergency beacon be sending some kind of intelligent signal, like SOS
in morse code, or some kind of RTTY? At the very least, a certain kind
of modulated tone. It seems to me that if they're going to chase after
every spurious signal that pops up on 121.5, no matter what it sounds
like, that's a recipe for failure. No wonder 90% of their hits are
false positives.

If you find yourself in a heap of burning airplane parts in some valley
one day, I really hope they're still looking for weak signals on that
frequency if your ELT gets damaged. You'll hope so, too.

--
Most dying mothers say, "I love you, son," or "Take care of your sister."
Why were the last words of Kerry's mother a lecture on integrity?

On Mon, 18 Oct 2004 00:57:07 -0500, clifto wrote:

Tony Calguire wrote:
What exactly are these search and rescue people listening for? Wouldn't
an emergency beacon be sending some kind of intelligent signal, like SOS
in morse code, or some kind of RTTY? At the very least, a certain kind
of modulated tone. It seems to me that if they're going to chase after
every spurious signal that pops up on 121.5, no matter what it sounds
like, that's a recipe for failure. No wonder 90% of their hits are
false positives.

If you find yourself in a heap of burning airplane parts in some valley
one day, I really hope they're still looking for weak signals on that
frequency if your ELT gets damaged. You'll hope so, too.
that's one of the reasons 121.5 Mhz ELT's are going away. They are
simply beacons, and any signal on 121.5 can be an ELT,maximum power
out is 100mw. The EPIRB and PLB use a digitally encoded 406Mhz signal
with a 5 watt output, and contains the beacon ID, and can also carry a
GPS determined position as a data payload. In addition all 406Mhz
units must be registered, because 121.5 and 243 Mhz units are not
encoded, they are not registered.

matt weber wrote in message . ..
On Mon, 18 Oct 2004 00:57:07 -0500, clifto wrote:

Tony Calguire wrote:
What exactly are these search and rescue people listening for? Wouldn't
an emergency beacon be sending some kind of intelligent signal, like SOS
in morse code, or some kind of RTTY? At the very least, a certain kind
of modulated tone. It seems to me that if they're going to chase after
every spurious signal that pops up on 121.5, no matter what it sounds
like, that's a recipe for failure. No wonder 90% of their hits are
false positives.

If you find yourself in a heap of burning airplane parts in some valley
one day, I really hope they're still looking for weak signals on that
frequency if your ELT gets damaged. You'll hope so, too.
that's one of the reasons 121.5 Mhz ELT's are going away. They are
simply beacons, and any signal on 121.5 can be an ELT,maximum power
out is 100mw. The EPIRB and PLB use a digitally encoded 406Mhz signal
with a 5 watt output, and contains the beacon ID, and can also carry a
GPS determined position as a data payload. In addition all 406Mhz
units must be registered, because 121.5 and 243 Mhz units are not
encoded, they are not registered.


And these REGISTERED units have the contactee's name and home phone
number. Within literally minutes, say like the Coast Guard, is calling
that person's home phone number to find out what the deal is.
Unfortunately, sometimes all they can get is the spouse of the
registered owner, and he or she don't have the faintest idea. All they
know is their husband or daddy does fly on the company plane once in a
while and he's away right now. But in the long run, it DOES save a lot
of needless searches for errant transmissions. And a heavy fine to
boot if set off fecklessly with no confirmation. 15 to 20 thousand
dollars per occurrance, if I remember correctly. If you do set one
off, especially an aircraft one, call 1-800-WXBRIEF and that number
will rotate your call to your nearest Flight Service Station to cancel
the inquieries and explain your situation. The days of CAP members
tramping all over the neighborhood all day searching for an accidental
trip are hopefully over.

And a heavy fine to boot if set off fecklessly with no confirmation.

Now, that's a funny thought -- a distress signal set off fecklessly.

"Brian Running" wrote in message . com...
And a heavy fine to boot if set off fecklessly with no confirmation.

Now, that's a funny thought -- a distress signal set off fecklessly.

Ha ha! Well maybe. I wasn't trying to be pretentious. I was simply
typing fast and for the life of me I couldn't think of an appropriate
word to use such as, 'carelessly' or better yet, 'irresponsibly'. I
find that being at a loss for words happening more often the older I
get!

In article ,
Tony Calguire wrote:
postal97321 wrote:
....
Ryan Gardner/Gazette-Times
Chris van Rossman's television sent out a distress signal that was
picked up by an orbiting satellite.
....

What exactly are these search and rescue people listening for? Wouldn't
an emergency beacon be sending some kind of intelligent signal, like SOS
in morse code, or some kind of RTTY? At the very least, a certain kind
of modulated tone. It seems to me that if they're going to chase after
every spurious signal that pops up on 121.5, no matter what it sounds
like, that's a recipe for failure. No wonder 90% of their hits are
false positives.

It's some sort of a warble tone on a carrier.

They use a transponder on polar orbiting satellites (weather and earth
sensing ones, usually) that allows the ground stations to do a doppler
measurement. Sort of the reverse of the Transit satellite navigation
system, where the timing and frequency shift of the signal allowed the
ground station to determine its position to a fraction of the meter.
The Transit system used atomic clocks, so the SARSAT accuracy would be
lower. But accurate enough to get the search and rescue close enough to
use portable direction finding gear.

Mark Zenier Washington State resident

(Mark Zenier) wrote in message ...
In article ,
Tony Calguire wrote:
postal97321 wrote:
...
Ryan Gardner/Gazette-Times
Chris van Rossman's television sent out a distress signal that was
picked up by an orbiting satellite.
...

What exactly are these search and rescue people listening for? Wouldn't
an emergency beacon be sending some kind of intelligent signal, like SOS
in morse code, or some kind of RTTY? At the very least, a certain kind
of modulated tone. It seems to me that if they're going to chase after
every spurious signal that pops up on 121.5, no matter what it sounds
like, that's a recipe for failure. No wonder 90% of their hits are
false positives.

It's some sort of a warble tone on a carrier.

They use a transponder on polar orbiting satellites (weather and earth
sensing ones, usually) that allows the ground stations to do a doppler
measurement. Sort of the reverse of the Transit satellite navigation
system, where the timing and frequency shift of the signal allowed the
ground station to determine its position to a fraction of the meter.
The Transit system used atomic clocks, so the SARSAT accuracy would be
lower. But accurate enough to get the search and rescue close enough to
use portable direction finding gear.

Mark Zenier Washington State resident

I bought an older (circa 1970) 121.5 ELT at a auction several years
ago.
And this unit had no modulation. Simple oscillator, followed by a
trippler,
a driver and a power amp. It had several shock switches in parallel.
This unit was designed to be clamped to the inside frame.
I always wondered just how well it radiate from the inside.
I have heard three ELTs, two hard landings, I live about 6 miles from
Lexington BlueGrass airport in Lexington Kentucky, and one was a
accidental trip in a local neighborhood. All three had a distinctive
"Wail" that is hard to discribe. I keep one scanner tuned to 121.5,
243 and some other hot freqs, and one Saturday morning I heard the
wailing of an ELT, and after 30 minutes, decided to go find it. With
my wife drivign and me RDFing it took us about 15 minutes.
I used a Pr02004 with an adjustable RF antenuator to find the street.
Then used my Pro34, wrapped in aluminium foil to narrow it down. We
listened to the CAP for the next 4 hours until they found it. I did
call the tower and tried to expalain what I had found, but they
thought me a kook.
Maybe the SAR satellite has to accept any signal on 125.5 as valid. I
do know that older ELT did not have moudlation. But I would have
expected the FAA/FCC to require replacement by of all of the older
units by now.
Terry

In article , lid
says...
What exactly are these search and rescue people listening for? Wouldn't
an emergency beacon be sending some kind of intelligent signal, like SOS
in morse code, or some kind of RTTY? At the very least, a certain kind
of modulated tone. It seems to me that if they're going to chase after
every spurious signal that pops up on 121.5, no matter what it sounds
like, that's a recipe for failure. No wonder 90% of their hits are
false positives.

Any signal, even a spurious one that conveys no intelligence, is
considered a problem because it could potentially cover up a weaker
signal from a person/aircraft/boat/etc. that is actually IN distress.

And for the record, if anyone cares, the manufacturer of the TV set
(Toshiba?) is replacing it with a new one free of charge, despite the
warranty having expired.

--

-- //Steve//

Steve Silverwood, KB6OJS
Fountain Valley, CA
Email: