Interference with FM radio, goes away when my hand is near.

In the last six months I've had interference with two FM radio
stations. I thought FM was immune to most interference?? So
what might be doing it?

It's so loud I can't hear the program,. But when I hold my fist very
near the radio or touching the front, the noise goes away gradually
and then completely when my hand is close enough. Is there some
way to duplicate the effect of my hand being near the radio???????
I tried a lot of things in a very different stituation and nothing I
tried worked.

Details.
It only happens sometimes, often in the middle of the night, and when
it's on one radio it's on two others also. Two have digital tuning
and one, maybe two, have analog (One digital is expensive 25 y.o,
the other maybe 10, one analog is transistor 40 y.o. or so. All of
them work well otherwise.) It often lasts only 15 minutes or less,
sometimes with interruptions with no noise. It may last longer other
times but I don't have the patience to keep checking. When I find
my mp3 player with FM radio, I'm going to walk around the n'hood and
see if I can find the source.

There's a bus with a 2-way radio that parks less than 100 yards from
my bedroom, but the noise occurs even when it's not thjre. My n'bors
all seem to keep regular hours, not up in the middle of the night,
and none have SWave antennas visible, and the noise has no words.

I live in Baltimore and it occurs on 88.5 and 90.1 MHz. FWIW these
are both DC stations 30 or 40 miles away, NPR and C-SPAN raido.. 88.1
which is local never gets interference. I don't know where other
stations on the dial are,located sine these are the only 3 I listen
to.

It sounds like a foghorn, a consistent deep (loud) tone, but a little
higher pitch than a real foghorn. .

Thanks.

micky wrote:
Interference with FM radio, goes away when my hand is near.

In the last six months I've had interference with two FM radio
stations. I thought FM was immune to most interference?? So
what might be doing it?

It's so loud I can't hear the program,. But when I hold my fist very
near the radio or touching the front, the noise goes away gradually
and then completely when my hand is close enough. Is there some
way to duplicate the effect of my hand being near the radio???????
I tried a lot of things in a very different stituation and nothing I
tried worked.

Details.
It only happens sometimes, often in the middle of the night, and when
it's on one radio it's on two others also. Two have digital tuning
and one, maybe two, have analog (One digital is expensive 25 y.o,
the other maybe 10, one analog is transistor 40 y.o. or so. All of
them work well otherwise.) It often lasts only 15 minutes or less,
sometimes with interruptions with no noise. It may last longer other
times but I don't have the patience to keep checking. When I find
my mp3 player with FM radio, I'm going to walk around the n'hood and
see if I can find the source.

There's a bus with a 2-way radio that parks less than 100 yards from
my bedroom, but the noise occurs even when it's not thjre. My n'bors
all seem to keep regular hours, not up in the middle of the night,
and none have SWave antennas visible, and the noise has no words.

I live in Baltimore and it occurs on 88.5 and 90.1 MHz. FWIW these
are both DC stations 30 or 40 miles away, NPR and C-SPAN raido.. 88.1
which is local never gets interference. I don't know where other
stations on the dial are,located sine these are the only 3 I listen
to.

It sounds like a foghorn, a consistent deep (loud) tone, but a little
higher pitch than a real foghorn. .

Thanks.

If it is in your residence, shut off the breaker to see if it stops on the
portable.

Greg

In article ,
micky wrote:
Interference with FM radio, goes away when my hand is near.

In the last six months I've had interference with two FM radio
stations. I thought FM was immune to most interference?? So
what might be doing it?

It's so loud I can't hear the program,. But when I hold my fist very
near the radio or touching the front, the noise goes away gradually
and then completely when my hand is close enough. Is there some
way to duplicate the effect of my hand being near the radio???????
I tried a lot of things in a very different stituation and nothing I
tried worked.

Details.
It only happens sometimes, often in the middle of the night, and when
it's on one radio it's on two others also. Two have digital tuning
and one, maybe two, have analog (One digital is expensive 25 y.o,
the other maybe 10, one analog is transistor 40 y.o. or so. All of
them work well otherwise.) It often lasts only 15 minutes or less,
sometimes with interruptions with no noise. It may last longer other
times but I don't have the patience to keep checking. When I find
my mp3 player with FM radio, I'm going to walk around the n'hood and
see if I can find the source.

There's a bus with a 2-way radio that parks less than 100 yards from
my bedroom, but the noise occurs even when it's not thjre. My n'bors
all seem to keep regular hours, not up in the middle of the night,
and none have SWave antennas visible, and the noise has no words.

I live in Baltimore and it occurs on 88.5 and 90.1 MHz. FWIW these
are both DC stations 30 or 40 miles away, NPR and C-SPAN raido.. 88.1
which is local never gets interference. I don't know where other
stations on the dial are,located sine these are the only 3 I listen
to.

It sounds like a foghorn, a consistent deep (loud) tone, but a little
higher pitch than a real foghorn. .

There is an older aviation navigation system, VOR, that runs in the range
just above the FM broadcast band (108-118 MHz). It works by broadcasting
a couple of tones at a low frequency, which, when compared, gives aircraft
a compass heading of their location relative to the airport that it's
located at.

It could be an RF Image. The usual IF for a FM receiver is 10.7
MHz, and the local oscillator is usually above the frequency, so a
super-heterodyne receiver can also be sensitive to signals 21.4 MHz
above the tuned station.

It might be a nearby airport, or it could be at a farther distance
than you would expect, especially now with the sunspots kicking up and
strange radio propagation effects can occur.

(The interference can go the other way, too, where the radio's local
oscillator will leak out and jam a VOR signal 10.7 MHz above the tuned
station's frequency. This is the main reason that personal electronics
are supposed to be turned off on aircraft at various times. Now, largely,
an obselete problem).

Mark Zenier
Googleproofaddress(account:mzenier provider:eskimo domain:com)

micky wrote in
:

On Mon, 19 Nov 2012 04:47:24 +0000 (UTC), gregz
wrote:

micky wrote:
Interference with FM radio, goes away when my hand is near.

In the last six months I've had interference with two FM radio
stations. I thought FM was immune to most interference?? So
what might be doing it?

It's so loud I can't hear the program,. But when I hold my fist
very near the radio or touching the front, the noise goes away
gradually and then completely when my hand is close enough. Is
there some way to duplicate the effect of my hand being near the
radio??????? I tried a lot of things in a very different stituation
and nothing I tried worked.

Details.
It only happens sometimes, often in the middle of the night, and
when it's on one radio it's on two others also. Two have digital
tuning and one, maybe two, have analog (One digital is expensive
25 y.o, the other maybe 10, one analog is transistor 40 y.o. or so.
All of them work well otherwise.) It often lasts only 15 minutes
or less, sometimes with interruptions with no noise. It may last
longer other times but I don't have the patience to keep checking.
When I find my mp3 player with FM radio, I'm going to walk around
the n'hood and see if I can find the source.

There's a bus with a 2-way radio that parks less than 100 yards from
my bedroom, but the noise occurs even when it's not thjre. My
n'bors all seem to keep regular hours, not up in the middle of the
night, and none have SWave antennas visible, and the noise has no
words.

I live in Baltimore and it occurs on 88.5 and 90.1 MHz. FWIW these
are both DC stations 30 or 40 miles away, NPR and C-SPAN raido..
88.1 which is local never gets interference. I don't know where
other stations on the dial are,located sine these are the only 3 I
listen to.

It sounds like a foghorn, a consistent deep (loud) tone, but a
little higher pitch than a real foghorn. .

Thanks.

If it is in your residence, shut off the breaker to see if it stops on
the portable.

Greg

Thanks. I will try that. but it's pretty quiet here in the middle of
the night**

Anyone have any idea how to duplicate the effect of my fist or hand
near the radio? That gets rid of the noise. I'm lying on a sheet
and mattress -- I don't think I'm grounded. A bag hung in front of
the radio filled with cooked chicken? Raw chicken? Metal scraps? I
can try the last one, but I'm not made of metal. Paperback books?

** only the furnace, fridge, and one outdoor IR triggered light. None
of them go on for a minute then off for a minute and back on. I can
tell t he furnace is not on all the time because the hot air vent is
right near me when the I'm in bed.



Your arm acts as an additional antenna, capacitively coupled.
This suggests that the orientation and/or antenna size is
bad for your location.
Attach a wire of about 2 meter to the antenna, and play with
the orientation.
Even better is to find the interference source, any modern switching
supply(computer, charger,GFL light,new fl light,senseo coffee) is a prime
candidate, even if you think the divice is switched off,
a lot of them still have an active computer chip and supply inside.

On Mon, 19 Nov 2012 04:47:24 +0000 (UTC), gregz
wrote:

micky wrote:
Interference with FM radio, goes away when my hand is near.

In the last six months I've had interference with two FM radio
stations. I thought FM was immune to most interference?? So
what might be doing it?

It's so loud I can't hear the program,. But when I hold my fist very
near the radio or touching the front, the noise goes away gradually
and then completely when my hand is close enough. Is there some
way to duplicate the effect of my hand being near the radio???????
I tried a lot of things in a very different stituation and nothing I
tried worked.

Details.
It only happens sometimes, often in the middle of the night, and when
it's on one radio it's on two others also. Two have digital tuning
and one, maybe two, have analog (One digital is expensive 25 y.o,
the other maybe 10, one analog is transistor 40 y.o. or so. All of
them work well otherwise.) It often lasts only 15 minutes or less,
sometimes with interruptions with no noise. It may last longer other
times but I don't have the patience to keep checking. When I find
my mp3 player with FM radio, I'm going to walk around the n'hood and
see if I can find the source.

There's a bus with a 2-way radio that parks less than 100 yards from
my bedroom, but the noise occurs even when it's not thjre. My n'bors
all seem to keep regular hours, not up in the middle of the night,
and none have SWave antennas visible, and the noise has no words.

I live in Baltimore and it occurs on 88.5 and 90.1 MHz. FWIW these
are both DC stations 30 or 40 miles away, NPR and C-SPAN raido.. 88.1
which is local never gets interference. I don't know where other
stations on the dial are,located sine these are the only 3 I listen
to.

It sounds like a foghorn, a consistent deep (loud) tone, but a little
higher pitch than a real foghorn. .

Thanks.

If it is in your residence, shut off the breaker to see if it stops on the
portable.

Greg

Thanks. I will try that. but it's pretty quiet here in the middle of
the night**

Anyone have any idea how to duplicate the effect of my fist or hand
near the radio? That gets rid of the noise. I'm lying on a sheet
and mattress -- I don't think I'm grounded. A bag hung in front of
the radio filled with cooked chicken? Raw chicken? Metal scraps? I
can try the last one, but I'm not made of metal. Paperback books?

** only the furnace, fridge, and one outdoor IR triggered light. None
of them go on for a minute then off for a minute and back on. I can
tell t he furnace is not on all the time because the hot air vent is
right near me when the I'm in bed.

In article ,
micky wrote:

In the last six months I've had interference with two FM radio
stations. I thought FM was immune to most interference?? So
what might be doing it?

FM is less vulnerable than AM, to impulse noise (static).

It's still vulnerable to both broadband noise, and narrowband noise,
if the strength of the noise signal comes close to (or becomes greater
than) the strength of the desired signal.

Most FM radios are also vulnerable to "desense" - a strong-enough
signal of any sort, located anywhere in the radio's RF passband (which
can be much wider than the FM band that you can tune) can saturate the
first stage or two of the radio's RF section. This has the effect of
making the radio less sensitive to the signal you want to hear - it's
as if the desired signal "fades out".

It's so loud I can't hear the program,. But when I hold my fist very
near the radio or touching the front, the noise goes away gradually
and then completely when my hand is close enough. Is there some
way to duplicate the effect of my hand being near the radio???????
I tried a lot of things in a very different stituation and nothing I
tried worked.

The fact that the interference fades out when you bring your hand near
the radio, makes me suspect the following:

(1) When the radio is being used normally, it's not actually getting a
strong signal from the station you want to hear.

(2) The interfering signal isn't actually that strong, either - but
when it gets into the radio's RF section it's at least as strong
as the signal you want to receive.

(3) When you hold your hand near the radio, your body is acting as an
auxiliary antenna - it's picking up and conducting the radio
station's signal on your skin surface. The signal is then being
"coupled" into the radio's antenna from your hand - capacitive
coupling.

(4) Your body is not acting as an efficient antenna for the
interfering signal, which suggests that the interference might
*not* be getting into the radio via the antenna, but via another
pathway (possibly the power line).

I live in Baltimore and it occurs on 88.5 and 90.1 MHz. FWIW these
are both DC stations 30 or 40 miles away, NPR and C-SPAN raido.. 88.1
which is local never gets interference. I don't know where other
stations on the dial are,located sine these are the only 3 I listen
to.

This is consistent with the problem being one which affects only weak
signals. 30 - 40 miles is a good distance for FM (it's probably
"medium fringe"), and stations such as NPR are likely to be smaller
(lower power) than big commercial stations.

Modern buildings often have a lot of metal in their structure,
reflective metal coatings on their windows, etc. - which tends to
weaken the FM signals pretty badly. I'm somewhat surprised that you
can get a decent-quality FM signal indoors from 30-40 miles away.

I think there are three approaches you can take to identifying the
problem:

(1) Locate the source of the interference, and either shut it down or
filter it at the source.

Switching off appliances and breakers, as has been suggested, is a
great way to do this... probably the easiest.

If the source is outside your house, you may need to go on a
"T-hunt" (transmitter hunt). A local ham-radio operator might be
able to help you with this... T-hunting is one aspect of the
hobby, and quite a few hams have directional antennas and the
skills needed to use them.

If you can find the source, but can't afford to shut it down
entirely, then connecting a plug-in RFI filter between the
appliance and the power line would probably help a lot.

(2) Filter the interference at your radio. The behavior you are
seeing makes me suspect that it may be getting into the radio via
the AC power cord. Adding a good plug-in RFI filter at the wall
outlet might choke off the interference before it gets into the
radio.

(3) Try to improve the strength of the radio signal that's getting to
your radio. Ideally, put up a simple outdoor antenna, and run a
coax cable to the radio. If the radio doesn't have an
external-antenna jack, you might be able to connect the coax to
the radio with a simple clip-lead jumper (from the coax center to
the radio's existing antenna), or connect two wires to the center
and braid of the coax and stretch these in opposite directions
near the radio.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

micky wrote in message
...
Interference with FM radio, goes away when my hand is near.

In the last six months I've had interference with two FM radio
stations. I thought FM was immune to most interference?? So
what might be doing it?

It's so loud I can't hear the program,. But when I hold my fist very
near the radio or touching the front, the noise goes away gradually
and then completely when my hand is close enough. Is there some
way to duplicate the effect of my hand being near the radio???????
I tried a lot of things in a very different stituation and nothing I
tried worked.

Details.
It only happens sometimes, often in the middle of the night, and when
it's on one radio it's on two others also. Two have digital tuning
and one, maybe two, have analog (One digital is expensive 25 y.o,
the other maybe 10, one analog is transistor 40 y.o. or so. All of
them work well otherwise.) It often lasts only 15 minutes or less,
sometimes with interruptions with no noise. It may last longer other
times but I don't have the patience to keep checking. When I find
my mp3 player with FM radio, I'm going to walk around the n'hood and
see if I can find the source.

There's a bus with a 2-way radio that parks less than 100 yards from
my bedroom, but the noise occurs even when it's not thjre. My n'bors
all seem to keep regular hours, not up in the middle of the night,
and none have SWave antennas visible, and the noise has no words.

I live in Baltimore and it occurs on 88.5 and 90.1 MHz. FWIW these
are both DC stations 30 or 40 miles away, NPR and C-SPAN raido.. 88.1
which is local never gets interference. I don't know where other
stations on the dial are,located sine these are the only 3 I listen
to.

It sounds like a foghorn, a consistent deep (loud) tone, but a little
higher pitch than a real foghorn. .

Thanks.

Is the interference a whine or a buzz?
Does it change pitch as well as volume , when you move close to it, like a
Therimin "musical" instrument

On 11/18/2012 10:47 PM, gregz wrote:
micky wrote:



In the last six months I've had interference with two FM radio
stations.

I live in Baltimore and it occurs on 88.5 and 90.1 MHz. FWIW these
are both DC stations 30 or 40 miles away, NPR and C-SPAN radio..


This is God's way of telling you to stop listening to liberal radio!
Mikek