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Electronics => RF, Microwave, Ham Radio => Topic started by: tariq on June 13, 2021, 12:24:49 pm

Title: how to remove noises in superheterodyne receiver
Post by: tariq on June 13, 2021, 12:24:49 pm

hi
i want use 433 Mhz remote and superheterodyne receiver.when i connect receiver data to microcontroller pin that pin becomes high and low continuously for i think every mili second or maybe less.when i press remote button i don't have any problem to determine requested rising edge and falling edge period time but in microcontroller i want to use interrupt when Rising edge comes  and because of these noises my microcontroller send interrupt for every 1 mili second or even less.I'm looking for a way to remove that Rising edge noises.
all the libraries i found in internet using interrupt to determine rising edge in receiver but i can't use the amount of interrupt in my code so is there any way to remove all that noises?
thank you

Title: Re: how to remove noises in superheterodyne receiver
Post by: radiolistener on June 13, 2021, 01:40:04 pm

you can use filter. Narrow bandwidth = less noise power. Narrow bandwidth means that you will needs more time to transmit the signal. If noise is too strong, you can use very sharp filter and transmit signal for several seconds in order to filter it from noise on receiver side. It requires several seconds to transmit the signal, but allows to work in noisy environment.

Title: Re: how to remove noises in superheterodyne receiver
Post by: Integrol on June 21, 2021, 07:24:49 am

radiolistener,

Can you explain why a Narrow bandwidth means that we will need more time to transmit the signal ?

I thought it depended only on the upper frequencies of the continuous band of frequencies and not on its width.

Thank you,

Title: Re: how to remove noises in superheterodyne receiver
Post by: bob91343 on June 22, 2021, 06:17:38 am

Narrow bandwidth restricts data rate.  See Mr. Nyquist.

Title: Re: how to remove noises in superheterodyne receiver
Post by: radiolistener on June 22, 2021, 11:06:22 pm

Quote from: Integrol on June 21, 2021, 07:24:49 am

Can you explain why a Narrow bandwidth means that we will need more time to transmit the signal ?

Because narrow bandwidth means that the signal should change slowly (at low frequency).

You cannot change signal at a quick speed, because bandwidth is limited. Shorter rise/fall time means higher frequency components in the signal, they require wide bandwidth.

When you use narrow bandwidth filter (in order to reduce noise influence), you will needs to use low frequency signal for the carrier modulation. So, it needs more time to detect it on receiver side, just because low frequency has longer period and needs more time to detect one period.

Quote from: Integrol on June 21, 2021, 07:24:49 am

I thought it depended only on the upper frequencies of the continuous band of frequencies and not on its width.

Absolute frequency value doesn't matter. Bandwidth matter.