radio reception oddity

R

RichD

Guest
I have an armband digital FM radio, for running.
The earphone cord is the antenna.

Reception is very sensitive to antenna orientation,
unsurprisingly. (a problem as I circle a track)
It's not the signal strength so much, but the noise
level varies greatly.

Anyhow, here's my question: the reception is
also highly sensitive to the radio orientation,
independent of the antenna. The noise again
varies a lot, as I rotate the package.

Can anyone explain this, in terms of circuitry or
physics? Is it normal, a product design flaw, or
defect in this particular unit?


--
Rich
 
RichD wrote:
I have an armband digital FM radio, for running.
The earphone cord is the antenna.

Reception is very sensitive to antenna orientation,
unsurprisingly. (a problem as I circle a track)
It's not the signal strength so much, but the noise
level varies greatly.
Click to expand...
I assume you've tried different stations with different signal levels?

Anyhow, here's my question: the reception is
also highly sensitive to the radio orientation,
independent of the antenna. The noise again
varies a lot, as I rotate the package.

Can anyone explain this, in terms of circuitry or
physics? Is it normal
Click to expand...
No, it's not normal.

a product design flaw or defect in this particular unit?
Click to expand...
Bingo.
That's most likely the reason.
Bet you have one of those cheap $5 no-name units...

Dave.
--
================================================
Check out my Electronics Engineering Video Blog & Podcast:
http://www.alternatezone.com/eevblog/
 
On Jun 18, 6:26 pm, RichD <r_delaney2...@yahoo.com> wrote:
I have an armband digital FM radio, for running.
The earphone cord is the antenna.

Reception is very sensitive to antenna orientation,
unsurprisingly.  (a problem as I circle a track)
It's not the signal strength so much, but the noise
level varies greatly.

Anyhow, here's my question: the reception is
also highly sensitive to the radio orientation,
independent of the antenna.  The noise again
varies a lot, as I rotate the package.
Click to expand...
This is normal in areas where noise is high and station signal
strength is low. I presume when you say "it's not signal strength so
much" what you mean is that it's not the music loudness varies so much
rather than it's that you are actually looking at a signal strength
display on the radio. If that is true then what is actually happening
is that the signal strength IS actually varying a LOT, and as it drops
down low the signal to noise ratio of the radio drops and you hear
lots of noise. The music volume doesn't change much be cause with FM
the volume depends on frequency shifts not signal strength.

This sort of thing is common because at FM frequencies wavelengths are
relatively short (a few feet) and this causes lots interference which
is not meaning "noise" but where one wave cancels another creating a
dreaded "dead zone"! Buildings, stadiums, even terrain will do this.
Plus FM antennas are rather directional (people building the radio
probably didn't give a damn about this) which makes the problems even
worse, Usually the answer is to listen to a stronger station which
won't drop out as much, even if you hate the music they play.

That's the basic story.
 
On Jun 18, 6:26 pm, RichD <r_delaney2...@yahoo.com> wrote:
I have an armband digital FM radio, for running.
The earphone cord is the antenna.

Reception is very sensitive to antenna orientation,
unsurprisingly.  (a problem as I circle a track)
It's not the signal strength so much, but the noise
level varies greatly.

Anyhow, here's my question: the reception is
also highly sensitive to the radio orientation,
independent of the antenna.  The noise again
varies a lot, as I rotate the package.

Can anyone explain this, in terms of circuitry or
physics?  Is it normal, a product design flaw, or
defect in this particular unit?

--
Rich
Click to expand...
 
"RichD"
I have an armband digital FM radio, for running.
The earphone cord is the antenna.

Reception is very sensitive to antenna orientation,
unsurprisingly. (a problem as I circle a track)
It's not the signal strength so much, but the noise
level varies greatly.
Click to expand...

** The signal level is varying greatly - that is how FM behaves.


Anyhow, here's my question: the reception is
also highly sensitive to the radio orientation,
independent of the antenna. The noise again
varies a lot, as I rotate the package.
Click to expand...

** Must be a bunch of signal bein gcapacitively coupled into the radio by
you body being in such close contact with it - the body makes a nice FM
antenna.

This "body" signal may well conflict in phase with that arriving from the
ear cord antenna and its level changes with postition and orientation on
your arm.

All normal behaviour for RF at that frequency.

Ignore that David Jones - he is a digital geek total moron.



...... Phil
 
RichD wrote:
I have an armband digital FM radio, for running.
The earphone cord is the antenna.

Reception is very sensitive to antenna orientation,
unsurprisingly. (a problem as I circle a track)
It's not the signal strength so much, but the noise
level varies greatly.
Click to expand...

FM uses limiting in the IF. That keeps the volume level, at any
received power level, but the signal to noise ratio drops along with the
received power level, which is typically specified in microvolts for
full quieting at the antenna input.

There is nothing odd about this, at all.


Anyhow, here's my question: the reception is
also highly sensitive to the radio orientation,
independent of the antenna. The noise again
varies a lot, as I rotate the package.

Can anyone explain this, in terms of circuitry or
physics? Is it normal, a product design flaw, or
defect in this particular unit?

--
Rich
Click to expand...

--
You can't have a sense of humor, if you have no sense!
 
"George Herold"

" ** Must be a bunch of signal being capacitively coupled into the
radio by you body being in such close contact with it - the body
makes a nice FM antenna."

Yeah! why does the body make such a good antenna?


** Animals and trees do well too.

I like testing
inputs, by grabbing on to a small screwdriver, and touching it to the
center pin of the BNC input. (All the 'crap' in the room gets coupled
in.)


** I read a story once about a radio repairman, long ago, who on making a
house call discoveed the sets owner had attached a length of salami to the
antenna terminal.

The owner reasoned that since his finger worked so well - why not
substitute a salami.



...... Phil
 
In article <7a0docF1s6q42U1@mid.individual.net>, Phil Allison
<phil_a@tpg.com.au> wrote:
** I read a story once about a radio repairman, long ago, who on making
a house call discoveed the sets owner had attached a length of salami
to the antenna terminal.

The owner reasoned that since his finger worked so well - why not
substitute a salami.
Click to expand...
When i were a kid working in a print shop, we had a flex off the radio
antenna point sat in a bucket of water. It worked brilliantly.

--
Terminal_Crazy

Mitch - 1995 Z28 LT1 M6 terminal_crazy@sand-hill.freeserve.co.uk
Lancashire England http://www.sand-hill.freeserve.co.uk/terminal_crazy/
 
On Jun 18, 9:49 pm, "Phil Allison" <phi...@tpg.com.au> wrote:
"RichD"

I have an armband digital FM radio, for running.
The earphone cord is the antenna.

Reception is very sensitive to antenna orientation,
unsurprisingly.  (a problem as I circle a track)
It's not the signal strength so much, but the noise
level varies greatly.

**  The signal level is varying greatly -  that is how FM behaves.

Anyhow, here's my question: the reception is
also highly sensitive to the radio orientation,
independent of the antenna.  The noise again
varies a lot, as I rotate the package.

** Must be a bunch of signal bein gcapacitively coupled into the radio by
you body being in such close contact with it - the body makes a nice FM
antenna.

This "body" signal may well conflict in phase with that arriving from the
ear cord antenna and its level changes with postition and orientation on
your arm.

All normal behaviour for RF at that frequency.

Ignore that David Jones  - he is a digital geek total moron.

.....  Phil
Click to expand...
"> ** Must be a bunch of signal bein gcapacitively coupled into the
radio by
you body being in such close contact with it - the body makes a nice FM
antenna."
Click to expand...
Yeah! why does the body make such a good antenna? I like testing
inputs, by grabbing on to a small screwdriver, and touching it to the
center pin of the BNC input. (All the 'crap' in the room gets coupled
in.)

George H.



>
 
In article
<6d95a077-4212-41ba-9440-ab18fbb733c0@c18g2000prh.googlegroups.com>,
RichD <r_delaney2001@yahoo.com> wrote:

I have an armband digital FM radio, for running.
The earphone cord is the antenna.

Reception is very sensitive to antenna orientation,
unsurprisingly. (a problem as I circle a track)
It's not the signal strength so much, but the noise
level varies greatly.

Anyhow, here's my question: the reception is
also highly sensitive to the radio orientation,
independent of the antenna. The noise again
varies a lot, as I rotate the package.

Can anyone explain this, in terms of circuitry or
physics? Is it normal, a product design flaw, or
defect in this particular unit?


--
Rich
Click to expand...
I cannot be definitive without examining the particular situation. I
would have to blame the equivalent of laser speckle for your problem
until it is proven otherwise. This phenomenon has analogs in multi-path
effects, acoustic room resonances, radar scintillation, star
scintillation, short wave fading, and the like. Much of this is missed
because pf the capture properties of FM.

Reflection and scattering cause a fine structure to the electromagnetic
field. Shining a red laser off of a rough wall causes a three
dimensional speckle pattern around the light spot on the wall. The same
thing happens throughout the entire electromagnetic spectrum albeit on a
scale proportional to the wavelength of the radiation. This effect
limits the quality of cell phone reception in the canyons of cities
with skyscrapers where there can be plenty of signal strength, but the
signal gets garbled anyway.

The distribution of signal strength follows a log normal distribution.
This means that there is a good chance that the signal drops close to
zero locally in the presence of large average signal.

If you look at laser speckle on a wall, you will see some very dark
spots in the pattern even though the average illumination is quite high.
I have personally taken a HeNe laser, placed it shining it up against a
wall to make a small spot. When viewing it from a short distance, it is
easy to see the speckle pattern. As you go farther away from the spot,
easier for your eye's pupil to fall in a dark spot in the random antenna
pattern generated by the laser spot with random phase across it. I was
able to move my head and eye so that the spot was completely dark and
not to be seen. Slight head motions made it possible to see a relatively
brightly illuminated laser spot. When you scale up to FM wavelength, the
signal drops out at such nulls and all you hear is noise.

Bill

--
Most people go to college to get their missing high school education.
 
George Herold Inscribed thus:

On Jun 18, 9:49 pm, "Phil Allison" <phi...@tpg.com.au> wrote:
"RichD"

I have an armband digital FM radio, for running.
The earphone cord is the antenna.

Reception is very sensitive to antenna orientation,
unsurprisingly.  (a problem as I circle a track)
It's not the signal strength so much, but the noise
level varies greatly.

**  The signal level is varying greatly -  that is how FM behaves.

Anyhow, here's my question: the reception is
also highly sensitive to the radio orientation,
independent of the antenna.  The noise again
varies a lot, as I rotate the package.

** Must be a bunch of signal bein gcapacitively coupled into the
radio by you body being in such close contact with it - the body
makes a nice FM antenna.

This "body" signal may well conflict in phase with that arriving from
the ear cord antenna and its level changes with postition and
orientation on your arm.

All normal behaviour for RF at that frequency.

Ignore that David Jones  - he is a digital geek total moron.

.....  Phil

"> ** Must be a bunch of signal bein gcapacitively coupled into the
radio by you body being in such close contact with it - the body makes
a nice FM antenna."

Yeah! why does the body make such a good antenna? I like testing
inputs, by grabbing on to a small screwdriver, and touching it to the
center pin of the BNC input. (All the 'crap' in the room gets coupled
in.)

George H.
Click to expand...
Primarily because the body is 70% water !

--
Best Regards:
Baron.
 
On Jun 19, 1:42 am, Salmon Egg <Salmon...@sbcglobal.net> wrote:

[Snip huge barf of crap]

When you scale up to FM wavelength, the
signal drops out at such nulls and all you hear is noise.

Bill

--
Most people go to college to get their missing high school education.
Click to expand...
Radio fading is laser speckle? :)

Bill, that was the most scientifically and intellectually opaque
pseudo-explanation for a common radio phenomenon I've ever heard. Let
us all PRAY that you have nothing to do with the technical education
of young people! God help us all.

idiot!
 
On Jun 19, 8:19 am, baron <baron.nos...@linuxmaniac.nospam.net> wrote:
George Herold Inscribed thus:
On Jun 18, 9:49 pm, "Phil Allison" <phi...@tpg.com.au> wrote:
"RichD"

"> ** Must be a bunch of signal bein gcapacitively coupled into the
radio by you body being in such close contact with it - the body makes
a nice FM antenna."

Yeah! why does the body make such a good antenna?  I like testing
inputs, by grabbing on to a small screwdriver, and touching it to the
center pin of the BNC input.  (All the 'crap' in the room gets coupled
in.)


Primarily because the body is 70% water !  
Click to expand...
Yeah that's it! It's like the guy with the wire going from the
antenna into a bucket of water! Taking a wire from the antenna
terminals and shoving it up your ass is exactly the same thing!
:)
 
Phil Allison wrote:
"RichD"
I have an armband digital FM radio, for running.
The earphone cord is the antenna.

Reception is very sensitive to antenna orientation,
unsurprisingly. (a problem as I circle a track)
It's not the signal strength so much, but the noise
level varies greatly.


** The signal level is varying greatly - that is how FM behaves.


Anyhow, here's my question: the reception is
also highly sensitive to the radio orientation,
independent of the antenna. The noise again
varies a lot, as I rotate the package.


** Must be a bunch of signal bein gcapacitively coupled into the
radio by you body being in such close contact with it - the body
makes a nice FM antenna.

This "body" signal may well conflict in phase with that arriving from
the ear cord antenna and its level changes with postition and
orientation on your arm.

All normal behaviour for RF at that frequency.

Ignore that David Jones
Click to expand...
The OP asked "Is it normal, a product design flaw, or defect in this
particular unit?"
It is generally not normal behaviour in a properly designed armband type
radio. So if it's as bad as the OP is making out then odds are he's got a
cheap badly designed radio. A better designed one will likely fix the
coupling problem at least.
I don't get the problem even on the weakest signals on my Creative MP3
player or Nokia phone for example.

But yeah, most likely his problem is capacitive coupling and phasing as you
say. Doesn't mean he has to put up with it.

And if his signals are that marginal in the area(s) he uses it, there is
always the MP3 option, along with podcasting of any particular radio
programs he might like to listen to.

Dave.
--
---------------------------------------------
Check out my Electronics Engineering Video Blog & Podcast:
http://www.alternatezone.com/eevblog/
 
"David L. Jones"
Phil Allison wrote:
"RichD"
I have an armband digital FM radio, for running.
The earphone cord is the antenna.

Reception is very sensitive to antenna orientation,
unsurprisingly. (a problem as I circle a track)
It's not the signal strength so much, but the noise
level varies greatly.


** The signal level is varying greatly - that is how FM behaves.


Anyhow, here's my question: the reception is
also highly sensitive to the radio orientation,
independent of the antenna. The noise again
varies a lot, as I rotate the package.


** Must be a bunch of signal bein gcapacitively coupled into the
radio by you body being in such close contact with it - the body
makes a nice FM antenna.

This "body" signal may well conflict in phase with that arriving from
the ear cord antenna and its level changes with postition and
orientation on your arm.

All normal behaviour for RF at that frequency.

Ignore that David Jones

The OP asked "Is it normal, a product design flaw, or defect in this
particular unit?"
Click to expand...
** And you told him the unit was faulty - which is 100% bullshit.


It is generally not normal behaviour in a properly designed armband type
radio.
Click to expand...
** Yes it is - you ignorant twat.

The OP is obviously in a very weak signal area, far from the transmitters
or behind a shadow created by terrain.

So piss the fuck OFF.



...... Phil
 
In article
<872a0887-b580-4e6e-b81d-3835710157d0@n8g2000vbb.googlegroups.com>,
Benj <bjacoby@iwaynet.net> wrote:

Bill, that was the most scientifically and intellectually opaque
pseudo-explanation for a common radio phenomenon I've ever heard. Let
us all PRAY that you have nothing to do with the technical education
of young people! God help us all.

idiot!
Click to expand...
Coming from you, I consider it a compliment.

Bill

--
Most people go to college to get their missing high school education.
 
Benj wrote:

On Jun 19, 1:42 am, Salmon Egg <Salmon...@sbcglobal.net> wrote:

[Snip huge barf of crap]

When you scale up to FM wavelength, the
signal drops out at such nulls and all you hear is noise.

Bill

--
Most people go to college to get their missing high school education.

Radio fading is laser speckle? :)

Bill, that was the most scientifically and intellectually opaque
pseudo-explanation for a common radio phenomenon I've ever heard. Let
us all PRAY that you have nothing to do with the technical education
of young people! God help us all.

idiot!
Click to expand...
Actually I would agree with Bill, since the underlying principle is
exactly the same ! Only the physical scale in terms of the length of
the wave would be larger at 90 - 100 Mhz.

--
Best Regards:
Baron.
 
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