Using headset as cell phone radio antenna.

[micky]

On Ebay, I bought a cell phone with FM radio, that gets the radio from
local stations, not from cell phone data, and after I bought it, I
found the manual online, which says that the radio antenna is the wire
to the earphones.

But the phone didn't come with the factory earphones.

Mostly I want to listen to 88.1 Mhz FM, and if possile 88.5, and
90.1frequencies.

For antenna purposes and those frequencies, are there any differences
from one headset to another?

Does the thickness of the copper wire matter?

Factory headphones may be impossible to get. without buying a second
phone. Should I try to find out how long the wire is on factory
earphones and get a headset with the same length?

Thanks.

 

[micky]

Yep. I have one like that. Motorola Droid X. The receiver
sensitivity is horrible and it only works in strong signal areas.

My friend had a Sony Ericson (model I forget, maybe w300i, several
years old) that worked well on 88.1, but the phone broke in other
ways, and her new phone is a Samsung something smart phone, and the
sound goes in and out, sometimes good, sometimes not. . She gets
consistently good reception on some commercial FM stations but 88.1
WYPR is public and she thinks the transmitter is weaker.

The station does come in well on my Sandisk Clip, a little MP3 player
about 1.5" almost square, but I've mislaid that.

Somewhat. There are headsets (4 wires) and earphones (3 wires).
Either will work. The problem is that some of the headsets come with
shielded wires, which will cause reception problems. I've only seen
one like this, and it has an easily identified thick cable.

Good. I'll avoid that.

No. In theory, tiny wire may add some resistance or reduce the tuned
bandwidth. In reality, the receive is so bad, you probably won't see
any differences.


Baloney. Such headsets are all over eBay.

I meant get an actual Huawei headset, but I gather I don't need that.

It would be helpful if you
would kindly disclose the maker and model of your phone.

Of course. It's a HUAWEI Fusion U8652, sold mostly by AT&T under
their brand. It has stereo radio with RDS I haven't got the phone
yet, it's still being shipped.

No. While getting the length correct, the lack of a counterpoise
(other half of the dipole) is probably more important. In ham radio,
it's called a "tiger tail".
<http://www.hamuniverse.com/htantennamod.html>
<http://pgh-net.com/ae3c/tiger-tail.html>
I played with it on my Droid X. It certainly improved reception, but
it was still lousy.

Maybe for us that would make the difference. Maybe we could each buy
one of those rubberized cases for the back, and coil it around in
there, relying on induction?

It should be 300,000,000 / 88,100,000 meters long? Or half that?
About 4 feet? Or 1/4 of the first number, 2 feet? I"ve never heard
of 1/8th wave, but maybe that works too? 1 foot?

I'm thinking of an external RF amplifier, but
suspect that will increase the sensitivity to the point where it will
pickup computah noise from the processor (which is why the receiver is
nearly comatose). Good luck.

Thanks.

 

[Terry Casey]

On Ebay, I bought a cell phone with FM radio, that gets the radio from
local stations, not from cell phone data, and after I bought it, I
found the manual online, which says that the radio antenna is the wire
to the earphones.

But the phone didn't come with the factory earphones.

Mostly I want to listen to 88.1 Mhz FM, and if possile 88.5, and
90.1frequencies.

For antenna purposes and those frequencies, are there any differences
from one headset to another?

Does the thickness of the copper wire matter?

Factory headphones may be impossible to get. without buying a second
phone. Should I try to find out how long the wire is on factory
earphones and get a headset with the same length?

Any set of headphones should work fine.

I have a Nokia with FM and the correct headset but always use it with
the earphones from my MP3 player (I don't use the phone hands free, so
don't need the microphone).

The screen (US: shield) of the cable is used as the aerial/antenna but
most (if not all) earphones use screened cable.

I don't think the length is going to be of any real consequence, though
a quarter wave whip @ 90MHz is ~80cm (~31 inches) if you want to try and
find a match!

 

[Terry Casey]

Somewhat. There are headsets (4 wires) and earphones (3 wires).
Either will work. The problem is that some of the headsets come with
shielded wires, which will cause reception problems. I've only seen
one like this, and it has an easily identified thick cable.

Wrong! The shield is used as the antenna!

 

[Terry Casey]

The station does come in well on my Sandisk Clip, a little MP3 player
about 1.5" almost square, but I've mislaid that.

The earphones I use for FM are the same ones I use on my Sandisk Sansa
MP3 player but they're Skull Candy, not the original Sandisk set

It should be 300,000,000 / 88,100,000 meters long? Or half that?
About 4 feet? Or 1/4 of the first number, 2 feet? I"ve never heard
of 1/8th wave, but maybe that works too? 1 foot?

It is (300/90)/4 metres. 300/90 = 3.33m (full wave)
Quarter wave is 3.33/4 = 83.33cm.

Antenna length is 95% of that - 79.16cm if you want to be accurate!
Or 31.17 inches.

For 88MHz, the length is 1.8cm/0.7in longer.

FM aerials are usually cut for the centre of the band (98MHz).
Corresponding lengths are 72.7cm/28.6in

However, this is all rather academic as these calculations are for a
whip in free space - not in close proximity to a human body!

For what it's worth, my 'phones are 1.22m/4 feet long ...

 

[Terry Casey]

If that's true, then why does my shielded cable earphones fail to hear
much on FM?

I've no idea!

Is it any better with unshielded cable?

All I can tell you is that my earphones are definitely shielded - I had
to replace the connector as the cable fractured - and that it works fine
with my phone!

<

>
Notice that he's connecting the antenna wire to the center pin, not
the ground.

Well he does say in the accompanying text that his FM reception is bad!

Interesting the way his 3-pole plug turns into a 4-pole one!

I can't tell what this one is doing:
<

>

Well, if he poked it any further into the jack he would have shorted the
audio output, so he obviously made contact with ground only (I'm
ignoring the mike connection, if there is one).

There is no way he could have made contact with the tip, like the
previous guy!

If I have time, I'll play with a connector and see which pin is the
antenna.

The shield should always be connected to ground, irrespective of whether
it's the barrel of the plug or one of the rings. Using a 3-pole plug
connects both together, anyway, so the shield will go to ground no
matter which way the jack is configured.

Note that it is not true ground, as far as the phone is concerned - it
is connected by an inductor which has negligible affect on audio
frequencies but a high impedance to the FM frequencies, thus allowing
the 'ground' connection to be used as the antenna.

 

[Terry Casey]

Well, you're 1/2 right (and I'm half wrong). The antenna is NOT the
shield but the shield is not the ground connection on the 3.5 mm
connector.

I inserted a 4 pin 3.5mm plug into my Droid X, and setup the FM tuna
to play through the speakers. Using a 2ft long clip lead as an
antenna, I probed all 4 pins on the connector to see what it could
hear. The sleeve (shield) connection did nothing and was the same as
no antenna. I couldn't even hear a local strong station. The tip and
the first ring picked up a few stations. However, the 2nd ring
connection produced dozens of stations (along with their RDS data), so
that must be the antenna wire.

But if the 2nd ring is ground, the shield should be connected to it ...

<http://encyclopedia2.thefreedictionary.com/Tip+Ring+Sleeve>
It's the TRRS connector, with connections marked as:
tip, ring 1, ring 2, and sleeve.
<http://i4.photobucket.com/albums/y136/invinciblegod/TRRSConnector3.png>
The typical wiring configuration is:
tip Left Earphone
ring 1 Right Earphone
ring 2 Ground
sleeve Microphone

If you plug a 3 pin TRS (tip-ring-sleeve) connector into a 4 pin TRRS
jack, ring 2 and the sleeve are connected together, thus grounding the
microphone connection.

.... which connects the shield of a 3-pin plug to 'ground' - which also
doubles as the antenna connection, as you have proved ...