FM radio interference from planes

I bought a FM wireless transmitter to rebroadcast stuff from my PC
around the house. The only frequency I could find was 104.1 that was
clear without a station. But all of a sudden, now when I am
broadcasting my stuff, I pick up planes instead. How can this be? I
know it is from planes, as I hear words like "Southwest", etc. Without
my transmitter on, all I hear is static on 104.1
but when I turn on my transmitter, the planes seem to over ride my
signal.

104.1 FM is below the aircraft navigation and below the
communication assigned frequencies. But there are harmonic
signals that you cheap FM transmitter is not screening out.
Are you using a wired connection from the PC to the FM
transmitter or a WiFi or other radio? Most likely you're
getting the interference in that way.

You may be in violation of FCC rules.


"rb" wrote in message
ups.com...
|I bought a FM wireless transmitter to rebroadcast stuff
from my PC
| around the house. The only frequency I could find was
104.1 that was
| clear without a station. But all of a sudden, now when I
am
| broadcasting my stuff, I pick up planes instead. How can
this be? I
| know it is from planes, as I hear words like "Southwest",
etc. Without
| my transmitter on, all I hear is static on 104.1
| but when I turn on my transmitter, the planes seem to over
ride my
| signal.
|

"Jim Macklin" wrote in message
news:AVTtg.67782$ZW3.26133@dukeread04...
[...]
You may be in violation of FCC rules.

Assuming he's using an off-the-shelf device intended for the use in which
he's applying it, that's extremely doubtful.

If he is broadcasting and his power is above the proper
legal range, he MAY be in violation. He should be sure the
FM transmitter he has, has an FCC number and is not causing
any interference with the neighbors.


"Peter Duniho" wrote in
message ...
| "Jim Macklin" wrote
in message
| news:AVTtg.67782$ZW3.26133@dukeread04...
| [...]
| You may be in violation of FCC rules.
|
| Assuming he's using an off-the-shelf device intended for
the use in which
| he's applying it, that's extremely doubtful.
|
|

"Jim Macklin" wrote in message
news:ASVtg.68472$ZW3.9262@dukeread04...
If he is broadcasting and his power is above the proper
legal range, he MAY be in violation.

Again, since it seems you didn't catch it the first time I wrote it:

Assuming he's using an off-the-shelf device intended for the use in which
he's applying it, that's extremely doubtful

He should be sure the
FM transmitter he has, has an FCC number and is not causing
any interference with the neighbors.

Whether he is causing any interference with the neighbors is irrelevant. As
long as it's approved by the FCC (and any off-the-shelf device intended for
the use in which he's applying it would be), the neighbors are required by
law to accept any interference (just as he and I and other people in similar
situations are required to accept interference from nearby AM transmitters).

Pete

Peter Duniho wrote:

"Jim Macklin" wrote in message
news:ASVtg.68472$ZW3.9262@dukeread04...
If he is broadcasting and his power is above the proper
legal range, he MAY be in violation.

Again, since it seems you didn't catch it the first time I wrote it:

Assuming he's using an off-the-shelf device intended for the use in which
he's applying it, that's extremely doubtful

Assuming that the device is properly constructed and adhering to standards that
is. Typically manufacturers can "self certify." YMMV.



He should be sure the
FM transmitter he has, has an FCC number and is not causing
any interference with the neighbors.

Whether he is causing any interference with the neighbors is irrelevant. As
long as it's approved by the FCC (and any off-the-shelf device intended for
the use in which he's applying it would be), the neighbors are required by
law to accept any interference (just as he and I and other people in similar
situations are required to accept interference from nearby AM transmitters).

You have that backwards. A part 15 device must not cause interference to
others. Conversely the user of the part 15 device must accept interference from
other users of the band. A local wireless (unlicensed) transmitter would
typically be a part 15 device.

This is assuming that the FCC has jurisdiction (i.e. USA).

The sender/generator of interference is required to take
steps to mitigate such and the others are expected to adjust
their antennas and equipment as needed. But that
presupposes that the transmitter is working with Part 15 and
is not a knock-off or non-certified device. Also, I'm not
trying to answer the question, I said he MIGHT be in
violation. I have not read Part 15 in the last few months
and I am not a ham or radio technician.

My original answer/question was about using a wire or radio
to get the desired signal from his PC to the FM transmitter.
If it is a wire and it is not properly shielded with good
grounds at both ends, it could be acting as an antenna input
to the FM. A wire will bring more signal, with less loss
than a WiFi, which should be well shielded.


"Peter Duniho" wrote in
message ...
| "Jim Macklin" wrote
in message
| news:ASVtg.68472$ZW3.9262@dukeread04...
| If he is broadcasting and his power is above the proper
| legal range, he MAY be in violation.
|
| Again, since it seems you didn't catch it the first time I
wrote it:
|
| Assuming he's using an off-the-shelf device intended for
the use in which
| he's applying it, that's extremely doubtful
|
| He should be sure the
| FM transmitter he has, has an FCC number and is not
causing
| any interference with the neighbors.
|
| Whether he is causing any interference with the neighbors
is irrelevant. As
| long as it's approved by the FCC (and any off-the-shelf
device intended for
| the use in which he's applying it would be), the neighbors
are required by
| law to accept any interference (just as he and I and other
people in similar
| situations are required to accept interference from nearby
AM transmitters).
|
| Pete
|
|

On Fri, 14 Jul 2006 16:43:15 -0700, "Peter Duniho"
wrote:

"Jim Macklin" wrote in message
news:ASVtg.68472$ZW3.9262@dukeread04...
If he is broadcasting and his power is above the proper
legal range, he MAY be in violation.

Again, since it seems you didn't catch it the first time I wrote it:

Assuming he's using an off-the-shelf device intended for the use in which
he's applying it, that's extremely doubtful

He should be sure the
FM transmitter he has, has an FCC number and is not causing
any interference with the neighbors.

Whether he is causing any interference with the neighbors is irrelevant. As
long as it's approved by the FCC (and any off-the-shelf device intended for
the use in which he's applying it would be), the neighbors are required by
law to accept any interference (just as he and I and other people in similar
situations are required to accept interference from nearby AM transmitters).


If it is a part 15 device (very low power no license required. This
includes the wireless mikes, remote speakers, remote weather stations,
WiFi computer networks, and a whole bunch of other *stuff*) the
*required* sticker on the back says two things. He *may not* cause
any interference and has to accept any he receives.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

Pete

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

Macklin, I like you, you are a nice guy. But sometimes you give advice that
is way the hell out of your depth. Like this one.



"Jim Macklin" wrote in message
news:AVTtg.67782$ZW3.26133@dukeread04...
104.1 FM is below the aircraft navigation and below the
communication assigned frequencies. But there are harmonic
signals that you cheap FM transmitter is not screening out.
Are you using a wired connection from the PC to the FM
transmitter or a WiFi or other radio? Most likely you're
getting the interference in that way.

You may be in violation of FCC rules.

Probably not, with a store-boughten transmitter. And harmonics (which are
integral multiples of a fundamental signal) probably have little to do with
it.

Consider the most probable cause. An FM receiver at 104.1 has a local
oscillator at 114.8 MHz to produce an IF of 10.7 MHz. Not only will that
beat with 104.1 on the low side of the LO, it will beat with 125.5 on the
high side. Most FM receivers have at least a +/- 50 kHz. wide IF strip to
allow the stereo subcarrier at 38 kHz. to come through, so 125.45, 125.5,
and 125.55 will come through as well.

The OP said that he doesn't get any interference when his transmitter is
off, so my best place to start looking is the front end of the receiver,
where the normal filtering of any decent FM receiver should take care of the
"image" problem. However, when a very strong signal (like from a 100 mW
legal transmitter) comes blowing into the front end of the receiver from a
few feet away, crossmod and intermod are NOT your friend, and no designer in
this world can make a brick wall filter that will take care of it.

Having said all that, the real problem is to keep whatever small amount of
aircraft band com energy is present at the front end from getting into the
receiver.

And, before we start off on a wild goose chase, I'd advise the OP to get a
small handheld aircraft band transceiver or scanner and see if the real
transmitter is somewhere around 125.5 MHz.. It is always good to be able to
do a math calculation to see exactly what is getting into what before
spending a lot of time chasing your tail.

For those who say "you can't hear AM on an FM receiver", I say
horsefeathers. It may be reduced in volume, it may be distorted, but it
will get through.

Do the test, tell me what frequency from 118-136.975 MHz. the aircraft is
on, and we'll go from there.

Jim

What did I say that was wrong [other than the typo you
should have been your]. The comment about FCC rules...they
do frown on transmitting or retransmitting the wrong
signals.

BTW, back in the 1974 period I gave a student a night dual
x-c from Tulsa to OKC and back one night. We picked up
several TV stations on the old AM radios in the C150 we were
flying. So bad radios, that do not have properly working
filters and signal rejection can do strange things.

We also had fun with CB radios in our cars back in the late
60's, parking outside a church or at the drive-in movie and
being able to have our comments come over the PA system.
Poor shielding let our 5 W CB radio get into their amp.

Some times you give criticism that isn't helpful. In my old
age, I do make misteaks [mistakes] and often brake rules
[break] because I sometimes remember the wrong bit of
information. And sometimes I'm right [correct] by accident.
mine..."| "Jim Macklin"
wrote in message
| news:AVTtg.67782$ZW3.26133@dukeread04...
| 104.1 FM is below the aircraft navigation and below the
| communication assigned frequencies. But there are
harmonic
| signals that you[r] cheap FM transmitter is not
screening out.
| Are you using a wired connection from the PC to the FM
| transmitter or a WiFi or other radio? Most likely
you're
| getting the interference in that way.
|
| You may be in violation of FCC rules.
|


--
The people think the Constitution protects their rights;
But government sees it as an obstacle to be overcome.
some support
http://www.usdoj.gov/olc/secondamendment2.htm
See http://www.fija.org/ more about your rights and duties.


"RST Engineering" wrote in message
...
| Macklin, I like you, you are a nice guy. But sometimes
you give advice that
| is way the hell out of your depth. Like this one.
|
|
|
| "Jim Macklin" wrote
in message
| news:AVTtg.67782$ZW3.26133@dukeread04...
| 104.1 FM is below the aircraft navigation and below the
| communication assigned frequencies. But there are
harmonic
| signals that you cheap FM transmitter is not screening
out.
| Are you using a wired connection from the PC to the FM
| transmitter or a WiFi or other radio? Most likely
you're
| getting the interference in that way.
|
| You may be in violation of FCC rules.
|
| Probably not, with a store-boughten transmitter. And
harmonics (which are
| integral multiples of a fundamental signal) probably have
little to do with
| it.
|
| Consider the most probable cause. An FM receiver at 104.1
has a local
| oscillator at 114.8 MHz to produce an IF of 10.7 MHz. Not
only will that
| beat with 104.1 on the low side of the LO, it will beat
with 125.5 on the
| high side. Most FM receivers have at least a +/- 50 kHz.
wide IF strip to
| allow the stereo subcarrier at 38 kHz. to come through, so
125.45, 125.5,
| and 125.55 will come through as well.
|
| The OP said that he doesn't get any interference when his
transmitter is
| off, so my best place to start looking is the front end of
the receiver,
| where the normal filtering of any decent FM receiver
should take care of the
| "image" problem. However, when a very strong signal (like
from a 100 mW
| legal transmitter) comes blowing into the front end of the
receiver from a
| few feet away, crossmod and intermod are NOT your friend,
and no designer in
| this world can make a brick wall filter that will take
care of it.
|
| Having said all that, the real problem is to keep whatever
small amount of
| aircraft band com energy is present at the front end from
getting into the
| receiver.
|
| And, before we start off on a wild goose chase, I'd advise
the OP to get a
| small handheld aircraft band transceiver or scanner and
see if the real
| transmitter is somewhere around 125.5 MHz.. It is always
good to be able to
| do a math calculation to see exactly what is getting into
what before
| spending a lot of time chasing your tail.
|
| For those who say "you can't hear AM on an FM receiver", I
say
| horsefeathers. It may be reduced in volume, it may be
distorted, but it
| will get through.
|
| Do the test, tell me what frequency from 118-136.975 MHz.
the aircraft is
| on, and we'll go from there.
|
| Jim
|
|