A superhetrodyne receiver works on the principle the receiver has a local oscillator called a variable frequency oscillator or V.F.O. which maintains a constant difference between itself and the received frequency resulting in a constant intermediate frequency.

WWW.ELECTRONICS-TUTORIALS.COM

LAST MODIFIED:

SUPERHETRODYNE RADIO RECEIVERS


What are the basics of a superhetrodyne radio receiver?

A superhetrodyne receiver works on the principle the receiver has a local oscillator called a variable frequency oscillator or V.F.O. which maintains a constant difference between itself and the received frequency resulting in a constant intermediate frequency

This is a bit like having a little transmitter located within the receiver. Now if we still have our T.R.F. stages but then mix the received signal with our v.f.o. we get two other signals. (V.F.O. + R.F) and (V.F.O. - R.F).

In a traditional a.m. radio where the received signal is in the range 540 Khz to 1650 Khz the v.f.o. signal is always a constant 455 Khz higher or 995 Khz to 2105 Khz.

Several advantages arise from this and we will use our earlier example of the signal of 540 Khz:

(a) The input signal stages tune to 540 Khz. The adjacent channels do not matter so much now because the only signal to discriminate against is called the i.f. image. At 540 Khz the v.f.o. is at 995 Khz giving the constant difference of 455 Khz which is called the IF frequency.  However a received frequency of v.f.o. + i.f. will also result in an i.f. frequency, i.e. 995 Khz + 455 Khz or 1450 Khz, which is called the i.f. image.

Put another way, if a signal exists at 1450 Khz and mixed with the vfo of 995 Khz we still get an i.f. of 1450 - 995 = 455 Khz. Double signal reception. Any reasonable tuned circuit designed for 540 Khz should be able to reject signals at 1450 Khz. And that is now the sole purpose of the r.f. input stage.

(b) At all times we will finish up with an i.f. signal of 455 Khz. It is relatively easy to design stages to give constant amplification, reasonable bandwidth and reasonable shape factor at this one constant frequency. Radio design became somewhat simplified but of course not without its associated problems.

Feedback to me.

RELATED TOPICS on superhetrodyne radio receivers

capacitance

diodes

inductance

resonant frequency

am radio receivers

radio receiver basics

tuned radio frequency TRF receivers

regenerative radio receivers

fm radio receivers



the author Ian C. Purdie, VK2TIP of www.electronics-tutorials.com asserts the moral right to be identified as the author of this web site and all contents herein. Copyright © 2000, all rights reserved. See copying and links. These electronic tutorials are provided for individual private use and the author assumes no liability whatsoever for the application, use, misuse, of any of these projects or electronics tutorials that may result in the direct or indirect damage or loss that comes from these projects or tutorials. All materials are provided for free private and public use.
Commercial use prohibited without prior written permission from www.electronics-tutorials.com.


Copyright © 2000, all rights reserved. URL - https://www.electronics-tutorials.com/receivers/superhetrodyne-radio-receivers.htm

Updated 13th July, 2000