Electronic Circuits and Projects Forum

I'm amazed you've got anything out of it, breadboards aren't suitable for RF - and the layout looks really awful!

Originally Posted by Nigel Goodwin

I'm amazed you've got anything out of it, breadboards aren't suitable for RF - and the layout looks really awful!

Thanks for your warm concern Nigel

I would expect the breadboard may create problem while implementing the LO and RF stages because it can certainly affect the desired band coverage. Other than that, the current setup is totally running on the 455KHz IF stage with external oscillator input injected, it seems almost fine. When we move on to higher frequency stages things will become worse I agree. So I may sometimes try the LO part on a separate pcb.

Regarding the worst layout and look, hey this was a very quick experiment actually done for testing my new signal generator, though it worked

The audio output is a clean compromise comparing to my previous super-regen.

I'll try to publish an article with latest circuit once everything is done, and this one uses very cheap components and 455KHz IFT's can be salvaged from any AM tranny/IC radios.

This one seems very easy

Originally Posted by transistor495

I'll try to publish an article with latest circuit once everything is done, and this one uses very cheap components and 455KHz IFT's can be salvaged from any AM tranny/IC radios.

So you're taking a radio to pieces to build a radio? - don't you spot the obvious flaw in that?

Many years ago there was a small junk shop for a while in a small town called Darley Dale, and a friend of mine lived near by - so I popped in once. They had a bucket full of new IF transformers, I often wished I'd bought a pile of them - but I didn't

Why do FM radios use wideband 10.7MHz IF transformers or crystal filters instead of the narrow band 455kHz ones used in AM radios??
Why do narrow band AM radios sound muffled with no high audio frequencies and are distorted, but half-decent FM radios sound extremely clear and produce almost all high audio frequencies without distortion??

Originally Posted by audioguru

Why do FM radios use wideband 10.7MHz IF transformers or crystal filters instead of the narrow band 455kHz ones used in AM radios??
Why do narrow band AM radios sound muffled with no high audio frequencies and are distorted, but half-decent FM radios sound extremely clear and produce almost all high audio frequencies without distortion??

What you've told I agree with you AG, to be honest I haven't even think about this while building this one and was very quick. I felt I'm missing the treble frequencies a bit in the audio but it's distortion free and lower frequencies are good. This one should provide more than 10KHz of audio bandwidth. Later I'll move on to 10.7MHz IF.

Nigel, I've collected a bunch of new IFT's before and contains different types may be 10.7 also in them I need to check it out.

Another thing I'd be experimenting here is the Foster-Seeley discriminator

I'll add detailed comments later.

In North America, AM radio stations are 10kHz apart so stations are not allowed to modulate with sound frequencies higher than 10khz to avoid beat frequencies in radios. Most AM radio stations use pre-emphasis equalization to boost audio frequencies from 2kHz to 5kHz to improve the intelligibility of speech through typical radios.

Wikipedia says that the audio response of the average AM radio is down 6 dB at 3 kHz and down
about 20 dB at 5 kHz. That is HORRIBLE audio frequency response like a telephone!

Originally Posted by audioguru

Why do FM radios use wideband 10.7MHz IF transformers or crystal filters instead of the narrow band 455kHz ones used in AM radios??
Why do narrow band AM radios sound muffled with no high audio frequencies and are distorted, but half-decent FM radios sound extremely clear and produce almost all high audio frequencies without distortion??

FM use 10.7MHz because it provides better image rejection.

Dual conversion FM receivers use 10.7(or more) first IF and 455KHz second IF to achieve better selectivity. Still with hi-fi audio.

If anybody concerned about the speciality of '.7' in 10.7, the reason is that the image frequencies would never fall on any other station as it'll always end up with an even number and the station frequencies will always be an odd ending.

Being an audiophile like audioguru, I'd never make compromise on the audio quality of my receiver.

Currently I"m doing the front-end part of my 455KHz IF transformer(!) based FM wideband receiver

Let's see and modify later on to 10.7MHz.