strange antenna effect...

[[email protected]]

I got a new used car, that has only a tape player (remember those?) and
radio.

I have a portable CD/mp3 player, and I also have a little transmitter I
got from Target a few years back, that takes a signal from a
walkman/CD/mp3 player, and broadcasts it to an FM channel of my choice
(frequency is adjustable by a screw in the back).

When driving with my contraption, I noticed that if I touched the
antenna of my transmitter, the volume on my car radio increased
significantly.

This really puzzled me. I thought that if I touch the antenna, the
signal should be less strong, since I would be basically a ground with
respect to the antenna.

Any thoughts?

I've thought about getting a CD/MP3 player for the car, but the tape
player/FM radio sounds pretty good, and I'm a bit afraid to buy
something that won't sound as good (FM-wise) as the stock Toyota radio.

 

[Joerg]

I got a new used car, that has only a tape player (remember those?) and
radio.

I have a portable CD/mp3 player, and I also have a little transmitter I
got from Target a few years back, that takes a signal from a
walkman/CD/mp3 player, and broadcasts it to an FM channel of my choice
(frequency is adjustable by a screw in the back).

When driving with my contraption, I noticed that if I touched the
antenna of my transmitter, the volume on my car radio increased
significantly.

Possible, if it is one of those cheap free-running oscillator things
where touching the antenna de-tunes its frequency. Then the radio might
sit on 88.9MHz and you xmit has drifted a few hundred kHz up or down.
That is why I plunked down a few bucks more for our TV modulator and got
one with a digitally programmable PLL transmitter.

Regards, Joerg

 

[René]

I got a new used car, that has only a tape player (remember those?) and
radio.

I have a portable CD/mp3 player, and I also have a little transmitter I
got from Target a few years back, that takes a signal from a
walkman/CD/mp3 player, and broadcasts it to an FM channel of my choice
(frequency is adjustable by a screw in the back).

When driving with my contraption, I noticed that if I touched the
antenna of my transmitter, the volume on my car radio increased
significantly.

This really puzzled me. I thought that if I touch the antenna, the
signal should be less strong, since I would be basically a ground with
respect to the antenna.

Any thoughts?

I've thought about getting a CD/MP3 player for the car, but the tape
player/FM radio sounds pretty good, and I'm a bit afraid to buy
something that won't sound as good (FM-wise) as the stock Toyota radio.

Radio has sliding mute. When signal gets weaker, mute is gradually
effected. Touching the TX antenna makes the signal stronger. I doubt
you get good stereo too (usually mixed to mono with weak signal)

Buy the CD/MP3 solution. I use it 3 hours a day while commuting,
MP3's, podcasts, E-books etc. Could not survive without. Had to kick
out the stock radio...replaced it with a JVC 4x50W.

A USB stick I/F is also nice though...

There is *no way* an FM TX -> radio sounds better.

 

[[email protected]]

Radio has sliding mute. When signal gets weaker, mute is gradually
effected. Touching the TX antenna makes the signal stronger. I doubt
you get good stereo too (usually mixed to mono with weak signal)

So this is normal - touch an antenna, signal gets stronger?

Do I become an extension of the antenna? (I'd thought I would be a
ground...)

Buy the CD/MP3 solution. I use it 3 hours a day while commuting,
MP3's, podcasts, E-books etc. Could not survive without. Had to kick
out the stock radio...replaced it with a JVC 4x50W.

A USB stick I/F is also nice though...

There is *no way* an FM TX -> radio sounds better.

Yes you're right. I'd meant if I wanted to listen to the local jazz FM
station, the radio sounds very nice.

Not sure if it's the radio or the speakers, that has such good bass...

 

[GregS]

So this is normal - touch an antenna, signal gets stronger?

Do I become an extension of the antenna? (I'd thought I would be a
ground...)

The device is opperating with too short of an antenna. I have a device installed in
one vehicle thats has a permanant Tee connection to the radio antenna.
The Target device seems like it should opperate with enough effective
radiated power, to give full noise quieting, but the settings may
be off on the radio. There should be muting control on the radio
as well as full off or on, as well as city settings.
Yes you do act as an antenna. In my car installation, I put a jack in to manually
feed the power amplifier if I want to play my CD/MP3 player, to bypass
my deck alltogether.
greg

 

[Rich Grise]

I got a new used car, that has only a tape player (remember those?) and
radio.

I have a portable CD/mp3 player, and I also have a little transmitter I
got from Target a few years back, that takes a signal from a
walkman/CD/mp3 player, and broadcasts it to an FM channel of my choice
(frequency is adjustable by a screw in the back).

When driving with my contraption, I noticed that if I touched the
antenna of my transmitter, the volume on my car radio increased
significantly.

This really puzzled me. I thought that if I touch the antenna, the
signal should be less strong, since I would be basically a ground with
respect to the antenna.

At FM broadcast frequencies (88-108 MHz), you body is a pretty effective
antenna itself - plus,you're adding a little bit of capacitive loading to
an antenna that's too short, and changing the matching at the output
stage. Do you have any clip leads? (you can get a 10-pack at RS for a
couple bucks) Clip one of them on the xmitter antenna, and just let it lie
there, and see if it has any effect.

Good Luck!
Rich

 

[[email protected]]

The device is opperating with too short of an antenna. I have a device installed in
one vehicle thats has a permanant Tee connection to the radio antenna.
The Target device seems like it should opperate with enough effective
radiated power, to give full noise quieting, but the settings may
be off on the radio. There should be muting control on the radio
as well as full off or on, as well as city settings.
Yes you do act as an antenna. In my car installation, I put a jack in to manually
feed the power amplifier if I want to play my CD/MP3 player, to bypass
my deck alltogether.
greg

Now that's brilliant! Where exactly do you solder the jack wires? Do
you solder on the same wires leading from the tape play head?

Do you also have to use an empty tape (with the tape ribbon removed) to
force the player to switch from radio to Tape mode?

 

[[email protected]]

The device is opperating with too short of an antenna. I have a device installed in
one vehicle thats has a permanant Tee connection to the radio antenna.
The Target device seems like it should opperate with enough effective
radiated power, to give full noise quieting, but the settings may
be off on the radio. There should be muting control on the radio
as well as full off or on, as well as city settings.
Yes you do act as an antenna. In my car installation, I put a jack in to manually
feed the power amplifier if I want to play my CD/MP3 player, to bypass
my deck alltogether.
greg

Wow, you put a jack in... details? schematics, photos...? Just solder
wires from the tape head, or would this be a bad idea?

 

[ehsjr]

So this is normal - touch an antenna, signal gets stronger?

Nope. There are too many variables to make that statement.
Sometimes stronger, sometimes weaker, sometimes no apparent
effect. It depends on the frequency, the device, the antenna
where it is touched and so forth.

Ed