Please visit VK2TIP's Book Shelf. My personal recommendations, thanks.
Wednesday, 18-Mar-2015 17:14:08 PDT
•NEW! ‣ - Amazon Electronic Component Packs. Check out the Amazon Electronic Component Packs page.
It doesn't matter whether you are a short wave listener, an A.M. radio dx'er, into hobby electronics or amateur radio design, the broad basic principles will still apply. Here we will briefly discuss the radio receiver basics as they apply to:
Basic crystal set.
A T.R.F. Receiver.
A Superhetrodyne Receiver.
The Reflex Receiver.
This electronics tutorials site is totally free for you to use and is financed wholly by click revenue derived from our sponsors who mainly advertise at the top of the pages and some other below. By visiting their different sites you demonstrate your very practical support for this valuable free site and for our sponsors as well. Thank you and enjoy my site.
1. The first receiver built by a hobbyist is usually the plain old crystal radio set. If you are unfamiliar with the design then check out the crystal radio set page.
2. The earliest receivers built were of the tuned radio frequency TRF variety. Here all the stages were made to tune simultaneously to the received frequency. Some tuned radio frequency TRF receivers we very elaborate but suffered a number of disadvantages overcome by the superhetrodyne principle.
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.
We will now consider these principles in depth by discussing a fairly typical a.m. transistor radio of the very cheap variety.
I have chosen to begin radio receiver design with the cheap am radio because:
(a) nearly everyone either has one or can buy one quite cheaply. Don't buy an A.M. / F.M. type because it will only confuse you in trying to identify parts. Similarly don't get one of the newer I.C. types.
Just a plain old type probably with at least 3 transformers. One "red" core and the others likely "yellow" and "black" or "white". Inside will be a battery compartment, a little speaker, a circuit board with weird looking components, a round knob to control volume.
(b) most receivers will almost certainly for the most part follow the schematic diagram I have set out below.
(c) if I have included pictures you know I was able to borrow either a digital camera or had access to a scanner.
Important NOTE: If you can obtain discarded or broken "tranny's" (Australian for transistorised am radio receiver) by all means do so because they are a cheap source of valuable parts. So much so that to duplicate the receiver as a kit project for learning purposes costs about $A70 or $US45. Incredible. That is why colleges in Australia and elsewhere can not afford to present one as a kit for students to construct.
Figure 1 - a.m. bcb radio schematic
There are no parts values shown as this schematic is purely for illustration puposes.
Such a receiver includes a reflex amplifier and is one which is used to amplify at two frequencies - usually both the intermediate and audio frequencies.
If you are involved in electronics then consider joining our "electronics Questions and Answers" news group to ask your question there as well as sharing your thorny questions and answers. Help out your colleagues!.
The absolute fastest way to get your question answered and yes, I DO read most posts.
This is a mutual help group with a very professional air about it. I've learn't things. It is an excellent learning resource for lurkers as well as active contributors.
crystal radio set
am radio receivers
radio receiver basics
tuned radio frequency TRF receivers
reflex radio receivers
regenerative radio receivers
superhetrodyne radio receivers
fm radio receivers
Looking for more? Visit my site map page:
This site is hosted at WebWizards.Net for better value.
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 - http://www.electronics-tutorials.com/receivers/receiver-basics.htm
Updated 15th September, 2000