long antenna

[RichD]

During my workout yesterday, I attached a 3 meter
extension to the earphone cord of my radio, as I
wanted to place it at a distance.
The cord is the antenna.

I was indoors, where the reception is usually crummy.
I figured the longer line should improve performance,
right? No! The reception was barely decipherable.

Can anyone explain the physics here?

--
Rich

 

[George Herold]

On Tuesday, November 17, 2015 at 1:39:04 PM UTC-5, RichD wrote:

During my workout yesterday, I attached a 3 meter
extension to the earphone cord of my radio, as I
wanted to place it at a distance.
The cord is the antenna.

I was indoors, where the reception is usually crummy.
I figured the longer line should improve performance,
right? No! The reception was barely decipherable.

Can anyone explain the physics here?

--
Rich

What frequency? Calculate the wavelength.

George H.

 

[Michael Black]

On Tue, 17 Nov 2015, RichD wrote:

During my workout yesterday, I attached a 3 meter
extension to the earphone cord of my radio, as I
wanted to place it at a distance.
The cord is the antenna.

I was indoors, where the reception is usually crummy.
I figured the longer line should improve performance,
right? No! The reception was barely decipherable.

Can anyone explain the physics here?

Was this AM or FM?

On AM (but the headphone cord isn't likely used for the antenna there),
there is so much electronic noise in the average house now that making the
antenna longer may just increase that noise. Getting the antenna near a
window will bring in more signal and less of the noise.

But it's like for the FM broadcast band. There may be issues with
multipath distortion, rearranging the headphone wire may help.

I once found a nice compact stereo system, but the "local" NPR station
(which isn't local) was noisy. I figured a better antenna, but that
didn't fix it. I removed the whip, and reception improved. So in that
case, the radio was being overloaded by local stations, which got in the
way of the weaker non-local station. But taking out the antenna meant a
reduction in the strength of the local signals, while the non-local was
still strong enough to come in, but no overloading from local signals.

Michael

 

[Phil Allison]

RichD wrote:

During my workout yesterday, I attached a 3 meter
extension to the earphone cord of my radio, as I
wanted to place it at a distance.
The cord is the antenna.

I was indoors, where the reception is usually crummy.
I figured the longer line should improve performance,
right? No! The reception was barely decipherable.

Can anyone explain the physics here?

** I assume you are trying to listen to local FM stations - right ?

The original earphone cord was matched to the radio's tuned circuits so that the combination resonates at or near the middle of the FM band at about 100MHz when used in the usual way. Adding extra extra length detuned that resonance to a lower frequency, outside the FM band.

In good signal conditions, this would hardly be noticed but in weak, indoor conditions it was enough to put the resulting signal below the threshold of reception.

IME radio signals behave as expected in outer space, with some predictability in free air and a line of sight but with no predictability indoors.


.... Phil

 

[Helmut Wabnig]

On Tue, 17 Nov 2015 10:38:58 -0800 (PST), RichD
<r_delaney2001@yahoo.com> wrote:

During my workout yesterday, I attached a 3 meter
extension to the earphone cord of my radio, as I
wanted to place it at a distance.
The cord is the antenna.

I was indoors, where the reception is usually crummy.
I figured the longer line should improve performance,
right? No! The reception was barely decipherable.

Can anyone explain the physics here?

can explain but not here.

has to do with reflections and standing waves.


w.