FM radio modification?

[bananasiong]

Hi,
I've a problem here, my cheap cheap manual tuning radio cannot function well. When I tune it to my favourite radio channel, the reception is not very clear. But for other channels are quite okay. Maybe because of that channel broadcast with lower power. It is not easy for me to tune to it. It is because the frequency display of my radio is less than 2cm! If i move a little bit to the tuner, i will hear other station's voice! They are too close to each other.
Can I do any modification on it? I don't mind if the bandwidth (88-108MHz) is decreased. I just want to listen to 99.7MHz.
And, when I hold the antenna with my hand, the sound seems to be louder. Why ??

Thanks.

 

[Hero999]

The signal gets louder when you hold the antenna because you're effectifly behaving like an antenna.

You could buy or even build a signal booster or better antenna for it.

 

[bananasiong]

Build a signal booster with touching anything in the radio?

 

[audioguru]

Hi,
I've a problem here, my cheap cheap manual tuning radio cannot function well. .....
Why ??

That is your problem. Its circuit is too cheap and simple.
A good FM radio has very good sensitivity and picks up stations far away at the same volume. The volume doesn't change if you touch the antenna, the station is there or it is not.
A good FM radio has very good selectivity. Even with a strong station beside a distant station, the distant station can be heard clearly without interference.

 

[Hero999]

It depends on what your idea of what a good FM radio is. A PLL will have excellent slectivity but will tend to reject distant stations and lock-on to a strong nearby signal. A high quality superhet won't be as selective but will still tune to a distant station dispite the existance of a strong local station nearby.

 

[audioguru]

If the RF is tuned and the IF filters are modern sharp-edge crystal filters then selectivity should be excellent. Good FM tuners don't have AFC (automatic-frequency-control) "to stop the stations from drifting". Stations don't drift, cheap radios do.

 

[bananasiong]

OH!! The only solution is to buy another 'non-cheap' radio.

 

[audioguru]

A cheap radio probably picks up strong local stations OK. That's what they are made for.

 

[bananasiong]

Yea, mine works fine for other stations, but not my favourite channel, bad luck...

 

[Hero999]

If the RF is tuned and the IF filters are modern sharp-edge crystal filters then selectivity should be excellent. Good FM tuners don't have AFC (automatic-frequency-control) "to stop the stations from drifting". Stations don't drift, cheap radios do.

My above statement is still correct. PLLs tend lock onto to strong signals and are more selective than the finest superhet. That's the whole point of a phase locked loop and is why they were designed into radios in the first place.

Radio stations don't normally shift unless you're travelling along in your car. FM radio stations that cover a large area often broadcast on different frequencies in different areas but they're very close to each other (in terms of frequency). My good quality car radio tends to lock-on to the strongest signal. If I travel from one area to another an a neighbouring station suddenly becomes much stronger than the one I'm listening to the station will suddenly change.

 

[audioguru]

My car radio and stereo FM tuner use frequency synthesizers for tuning. They don't change frequency by themselves to lock onto a neighbouring station's frequency.

Maybe you are talking about "capture ratio" where a tuner will suddenly switch to a slightly stronger different station that is on exactly the same frequency. Good superhet radios also have excellent capture ratios.

 

[stevez]

You might try a directional antenna but this only works if the station of interest is not in the same direction (or nearly 180 degrees from) as the stations on nearby frequencies. A directional antenna with a proper transmission line should increase the signal level to the receiver in the direction that it is pointed - and it will provide reduced signal level for stations not in that direction.

To purchase the materials and construct such an antenna would probably require as much effort as replacing the radio but it may be a solution that works for you.

Adding length alone to your existing antenna may or may not help. The signal level of the desired station may go up but so will the others - which may make the problem worse. It would seem easy enough to try.

 

[Nigel Goodwin]

Maybe you are talking about "capture ratio" where a tuner will suddenly switch to a slightly stronger different station that is on exactly the same frequency. Good superhet radios also have excellent capture ratios.

It sounds more like he's talking about RDS?, where the radio changes automatically to the strongest transmitter for the station you are listening to! - VERY, VERY, common on car radios!.

 

[audioguru]

My car radio displays the type and call letters of FM stations but doesn't automatically switch stations. I can hear a couple of robot American stations with the same program, maybe it will automatically switch between them. The FM stations in Canada aren't robots and are all different.

 

[Nigel Goodwin]

My car radio displays the type and call letters of FM stations but doesn't automatically switch stations. I can hear a couple of robot American stations with the same program, maybe it will automatically switch between them. The FM stations in Canada aren't robots and are all different.

If stations don't have multiple transmitters than obviously there's no RDS information for them to switch - in the UK there are national BBC stations, with different transmitters all over the country - your car radio automatically switches to the strongest one as you drive round.

Even my local radio station 'Peak FM' has two transmitters, 107.4 and 102, and my radio switches between them going to and from work. The switching is pretty seemless, you rarely notice it.

 

[audioguru]

North American FM frequencies are odd-numbered. Are they even-numbered in the UK? Can you pickup FM stations from France? Are they even or odd?

 

[Nigel Goodwin]

North American FM frequencies are odd-numbered. Are they even-numbered in the UK? Can you pickup FM stations from France? Are they even or odd?

The UK uses both, as far as I'm aware so does the rest of Europe?, but I'm too far away to get non-UK stations.

Europe uses a different channel spacing to the USA, I can't remember what it is off hand - but you often see it speciifed in service manuals.

 

[Tarsil]

Build a tuned amplifier for that freq using a cheap transistor like BFR91A or whatever. About the freq drift...If the radio is batery powered modify it and use a well stabilized PS. Varying imput voltage afects the veractor diode's capacitance (that if the radio uses a veractor diode ).

 

[Hero999]

I know about RDS, but even if the radio station in the other are is different to the one I'm listening too, it still tends to switch to it.

 

[Nigel Goodwin]

I know about RDS, but even if the radio station in the other are is different to the one I'm listening too, it still tends to switch to it.

That's not RDS then, it's just one signal swamping the other one, either on the same frequency or very close to it.