How to establish what is the source of noise in AM receiver?

[amriths04]

hi friends,
i just now constructed an am receiver. when i tuned it i was only able to hear a (whish) sound throughout my tuning range. now my doubt is how can we differentiate that whether the noise is from power supply or whether there is no station within my tuning range.
because, only then i may be able to know whether there is a problem in my connection or my range is not proper.
is there any practical and efficient solution to this?

thank you in advance.

 

[Sal]

what noise?

Hello

I am surprised how easily you blame the power supply for the noise you hear. It can come from many parts of your circuit, considering you build this circuit, a good check (the correct tuning of the filters, right polarization of the transistors, etc.) is the first step. in order to dircard the possibility of malfunction the easiest way may be to find a working radio in the same band.

Sal

 

[flatulent]

Re: what noise?

Here is the classical way to do the test without test equipment,

Connect and disconnect the antenna several times. If the noise is higher with the connect, the noise is from the outside world. Above 30 MHz, it is common for the receiver input noise to be larger than the atmospheric noise.

Power supply noise will be spectral lines at harmonics of the mains frequency. Listen for low frequency hum.

 

[amriths04]

Re: what noise?

ya i hear a change in the noise intensity when i connect and disconnect the antenna.

also when i take any metal object near the tuning capacitor, i hear a louder sound.

but the main thing is that i took the inductor coil from an old radio set and i dont know it's inductance. i have only air core inductance calculator software in my system. and what i am using is a ferrite core. and i use a 2-22pf varicap along with it for tuning.

so i am really unable to determine under which frequency my radio is operating.

Here is the classical way to do the test without test equipment,

Connect and disconnect the antenna several times. If the noise is higher with the connect, the noise is from the outside world. Above 30 MHz, it is common for the receiver input noise to be larger than the atmospheric noise.

Power supply noise will be spectral lines at harmonics of the mains frequency. Listen for low frequency hum.

 

[Learner]

Re: what noise?

You need to get an oscillator and sweep the frequency into the tuner to check for the resonance frequency of your tuner.