radio noise

[epilot]

hi there

i have a MW radio for repair but it has no component problem ,
the real problem is from the home voltage(220v)...
the radio has alot of noises at all frequances...
does anyone know how i can ignore this noise?

i think i need for a kind of filter but dont know more....

thanks for any input

 

[Russlk]

If you have flourescent lights, these generate a lot of noise that is picked up by the antenna. The only solution I know of is to move the antenna away from the lights. If flourescent lights is not the problem, then most likley the power supply filtering is bad or you may need to add a noise filter to the input line.

 

[epilot]

thanks for the relpy ino the antenna is not the problem
the problem is from the supply...

dpo you know if i have to bbuy an filter or amke one myself?

what kind of filter i need?

 

[Nigel Goodwin]

thanks for the relpy ino the antenna is not the problem
the problem is from the supply...

dpo you know if i have to bbuy an filter or amke one myself?

what kind of filter i need?

How do you know it's from the mains?, this would be very unusual?.

 

[epilot]

becuase when i go to a place with no mains i have no a such problem...
i have this problem even when i use from batterys as supply
i have this problem with old an cheap radios and the expensive radios have not this problem.. i am sure this problem is because the cheap
radios dont use from filters at the suplly part

i am pretty sure that the problem is from the mains transformers..

 

[JimB]

becuase when i go to a place with no mains i have no a such problem...

OK so there is noise which appears to be due to the mains supply.

i have this problem even when i use from batterys as supply

So when you run the radio from the battery, you do have the noise problem, OK

i have this problem with old an cheap radios and the expensive radios have not this problem.. i am sure this problem is because the cheap
radios dont use from filters at the suplly part

i am pretty sure that the problem is from the mains transformers..

You are now contradicting yourself!
You said there was a problem when using a battery supply, but now you say that an expensive radio is OK, is that in mains or battery?
Please get your facts straight!

JimB

 

[epilot]

Jim,
if you read all the posts you can see that there was a post by "Russlk",
he said that the problem may be from the florescent lights...i wanted to say the the problem is because of mains, so a radio hase to have a filter for ignoring the noise cause by the mains..
the expensive radios have an filter but the cheap and old radios(AM radios) dont have commonly
if you think there was a contradicting about the mains and the batteris supply then i must say the my mean about "i have this problem even when i use from batterys as supply " is that the problem is from the 220V cables at the home and the street and if i use from the batteries in the city the problem will not lose, but at out of the city i have no problem.

the only solvation i know is using from the filters but i dont know what kind of filters are ok.

hope i could say me maen with my bad english lang

 

[Russlk]

If you have the noise when operating from a battery, then mains filter will not help. Perhaps the noise is coming in the intermediate frequency (IF) in which case shielding the chassis with aluminium foil may help.

 

[JimB]

If you have the noise when operating from a battery, then mains filter will not help. Perhaps the noise is coming in the intermediate frequency (IF) in which case shielding the chassis with aluminium foil may help.

Possible, but unlikely I think.

One thing that occurs to me, are the "cheap radios" AM only and the "expensive radios" have FM?
FM has noise rejection features and operates at VHF, where the noise (usually) cant reach.

JimB

 

[stevez]

Your mention of "MW" suggests AM broadcast band or somewhat higher frequencies. You might want to clarify the range of frequencies and mode (AM, FM, etc).

If it's AM mode then the more expensive radio might have a noise blanker or similar feature where the other does not. A noise blanker doesn't make the noise go away - it mutes the reciever for the duration of the pulse - the duration is hopefully very short and not noticed.

Is it possible that one kind of detector might be more sensitive to noise than another - for AM? I don't know the answer - others here might.

Describe the noise. It it continuous, with no gaps or does it come and go as you tune up or down the band?

I live in a moderately noisy area and almost gave up on problems like this. One day I decided to do some experiments. I had my radio going and shut all the power off - some noise went away - enough that if it were always gone I'd be happy. I turned the power on, one circuit at a time, until the noise returned. There were several sources. The worst was a touch lamp - I got rid of it. I could reduce but not eliminate the noise. My microwave, computer and refrigerator also contributed. The computer was off but still plugged in - had to unplug to get rid of the noise. The touch lamp was the worst and I live with the rest. You might do a similar experiment.

Powerful transmitters can overload the front end of a reciever and make it look like there are noises or stations where there are none. Some better (usually more expensive) recievers are more immune that the cheaper units. A filter on the antenna to pass only the frequencies of interest - or to block the overloading frequencies - is the solution.

Hope this helps.

 

[zhi_yi]

hi there, i am newbie, and have a lot of question, please help me

If you have flourescent lights, these generate a lot of noise that is picked up by the antenna <-- why the fluorescent lights generate noise?

If you have the noise when operating from a battery, then mains filter will not help. Perhaps the noise is coming in the intermediate frequency (IF) in which case shielding the chassis with aluminium foil may help <-- what is intermediate frequency?

One thing that occurs to me, are the "cheap radios" AM only and the "expensive radios" have FM?
FM has noise rejection features and operates at VHF, where the noise (usually) cant reach. <-- what is the range of noise? how is the bandwidht of noise??

what is the application of BPF and BSF??

thank you

 

[Russlk]

The flourescent light is basicly an arc, which is the reason it is noisy.

Do a Google search for "superhetrodyne" it will explain IF frequency.

BPF: band pass filter, used to pass a desired frequency and reject others.

BSF: band stop filter, used to reject an unwanted frequency and pass others.

 

[zhi_yi]

okay, thank you russlk

and.. the band pass filter, maybe i used a lot of grammar error i mean what is the application of the band pass filter, not the function, for example, the high pass filter could be used for audio system in modify the treble, the low pass filter for bass, and how about the band pass filter, band stop filter, and allpassfilter??

thank you very much

 

[Russlk]

An allpass filter is used to change the phase of the signal without changing it's amplitude. Filters always change the phase of the signal and sometimes that is objectionable. An allpass filter can correct the phase shift caused by another filter.

A bandstop filter is used to remove noise or interference. A notch filter might be used to remove 120 Hz hum, for example.

Bandpass filters are used in audio equalizers, and the IF amplifier in a superhet radio is a bandpass filter.

 

[zhi_yi]

please tell me what kind of filter that caused the phase shifted, so we need the allpassfilter to correct it

what is 120 Hz Hum??



thank you very much ,


zhi yi

 

[Russlk]

non-linear phase shift causes distortion of the waveform. The ideal is to have linear phase shift with frequency, so an allpass filter would be designed to linearize the phase shift of another filter.

The power frequency in the US is 60 Hz which is full wave rectified producing 120 Hz ripple. In Europe, the ripple would be 100 Hz.

 

[zhi_yi]

non-linear phase shift causes distortion of the waveform. The ideal is to have linear phase shift with frequency, so an allpass filter would be designed to linearize the phase shift of another filter. <-- so, what caused the non linear phase shift??

The power frequency in the US is 60 Hz which is full wave rectified producing 120 Hz ripple. In Europe, the ripple would be 100 Hz. <-- so the bandstop filter could be use to reduce the ripple in the output from power supply??

i am sorry for the incorrect grammar i used

thank you very much

 

[Russlk]

what caused the non linear phase shift??

Pure inductance produces a 90 degree phase lag of current with respect to voltage. When there is resistance in series with the inductance (and
there is always some resistance in the real world), the phase angle varies with frequency. The phase angle depends on the ratio of inductive reactance and resistance. The resistance is fixed but the reactance varies according to the equation: Xl = 2* PI *F * L. The reactance (Xl) is a linear function of frequency but because it is at 90 degrees relative to the resistive component, the phase versus frequency is non-linear. The phase angle is 0 at zero frequency (if you can imagine phase at zero frequency!), 45 degrees at the frequency where Xl=R and 90 degrees at infinite frequency.

A similar argument holds for capacitance except the current in a capacitive circuit leads the voltage and the capacitive reactance has the equation: Xc = 1/(2*PI*F*C).

so the bandstop filter could be use to reduce the ripple in the output from power supply??

That could be done, but in practice a low pass filter is used to pass the DC and reject 120 Hz and all higher frequencies.

 

[Nigel Goodwin]

I think this is getting a little carried away :lol:

We're only discussing interference on a cheap MW radio, I still don't think it's been confirmed WHERE the interference is entering? - mains, RF, or perhaps directly in the IF?.

There seems little point getting complicated about filters, when we don't even know where (or what) it might be used for.

The main complain (as I see it?) appears to be that an expensive radio is better than a cheap radio - personally I don't find that surprising?. I thing it's probably unlikely to be down to adding some magical filter, just that the overall design is going to be better right through.

I can't remember the last time I ever used an AM radio?, although I still have one of the best ever made, a Hacker RP35. For those of you who have never heard of Hacker, they made the BEST portable radios in the world! - bar none!. Unfortunately, people ceased to be prepared to pay for quality, and Hacker went bust :cry:

I bought mine second hand in 1971, it was the loudest portable radio you ever did hear :lol: it runs off 18V - two PP9's in series, and has a large elliptical speaker.