Superheterodyne FM receiver

[YuridaE]

Superheterodyne AM receiver

Hi, Im building a superheterodyne AM receiver.

Im going to build every circuit from scratch
-RF amplifier
-Mixer
-Local Oscillator
-IF amp IF amp
-Audio Amp

Any idea on how to begin my project? I want to implement it in breadboard but first i need to simulate it.

 

[audioguru]

You cannot make an FM radio circuit on a breadboard. The many rows of contacts and wires all over the place have much too much capacitance between them.
You will not be able to simulate the many tuned circuits. You cannot simulate modern ceramic filters in the IF.

 

[crutschow]

That's a very ambitious project. Have you built any RF circuits previously?

 

[Nigel Goodwin]

That's a very ambitious project. Have you built any RF circuits previously?

Not really that ambitious, as it's VERY old technology - essentially all you need is a service manual for a 40+ year old radio

But I agree with AG - breadboarding (apart from the audio stages) wouldn't work.

 

[RadioRon]

A project of this sort must be built in a modular form. This means that you should build each of those circuits separately and test each one in turn. Each one that you build becomes your test equipment for the next one. So, for example, you would first build the audio amp, partly because it is the easiest, but also because it becomes your test equipment for checking the next stage. Next, you should add the deemphasis network and then check it by using a meter at the output of the audio amp. When this is working ok, then build the discriminator on a separate board and test it. When that is working, then build the limiter and then test it. As you can see, at each step, you will have only one stage that is or is not working correctly so you won't be overwhelmed with many faults or errors at one time.

For each circuit, you will need to research how the circuit works, then design your own in schematic form, then build and test. The circuits should each be built on circuit board, either by cutting a board using a knife, by using a pad-per-hole type and point to point wiring, or by etching a pattern on the board.

You might call this approach "baby steps" but it is by far the most likely to succeed. So, to start with, you need to build an audio amplifier. What are the features and specs for this amplifier?

 

[audioguru]

I wonder if parts to make a radio are still sold? Multi-gang variable capacitors, ceramic filters or old IF transformers?
Maybe somebody makes a kit for an FM radio?
Or buy an FM radio, take it apart then put it back together.

DO NOT buy the "FM Radio" at The Dollar Store because it is so cheap that it barely works.

 

[crutschow]

Not really that ambitious, as it's VERY old technology - essentially all you need is a service manual for a 40+ year old radio

It may be VERY old technology, but that doesn't make it easy. Building a high gain analog circuit to operate with an RF frequency of 100 MHz and and an IF of 10.7 MHz from scratch still requires a fair amount of RF expertise to lay it out correctly for proper operation without spurious responses or oscillation, and some good test equipment to align and test it.

 

[schmitt trigger]

I agree with A.G.
Get yourself a discarded FM radio, study the schematic, then scavenge the key components.
Then assemble it on a board, one stage at the time....
You'll require some test equipment to align the coils.

 

[audioguru]

Get yourself a discarded FM radio.

Because an ordinary FM radio is not made and sold anymore?
An iphone has an FM radio and some appliances have an FM radio today.

The AM-FM radio stopped working on my 16 years old home stereo but I do not know when it stopped (maybe a few years ago?) because I play FM radio from the internet. Its amplifier still works fine.
I haven't used my 35 years old Sony Walkman FM radio for a few years. I haven't used the 49 years old stereo in my computer room for a few years.
But I use the FM radio in my car every day.

Instead of trying to decode single tones (lots of interference), have you consided using DTMF (telephone dual touch-tones) that are produced by one IC and are decoded by another IC?

Yikes! There is a blizzard outside now!

 

[MikeMl]

Simulation at VHF is difficult unless you have access to $100,000 software.
Breadboarding at VHF doesn't work because circuit operation at VHF is totally dependent on circuit layout

 

[audioguru]

Maybe this student should make a simple AM broadcast band radio or an AM crystal set.

 

[YuridaE]

Ok, im gonna build now an AM superheterodyne Receiver. can you help me?

 

[cowboybob]

Start by deciding whether you want a "tube type" or "solid state" receiver circuit: (both have pros and cons)

Google "AM superheterodyne tube receiver circuit" or simply "AM superheterodyne receiver circuit".

There's tons of stuff out there on both types, some specifically suggesting "bread boarding" your initial trials.

Not knowing your level of expertise, though, I'm with audioguru on a starting point.

 

[schmitt trigger]

I have an idea;
if you want to learn the basics of superhet receivers, purchase yourself a kit.

The following is a highly rated one, as it not only includes all components and a very nice board, but its assembly manual is written in tutorial form such that you understand how each circuit block works as you build it.

**broken link removed**

 

[YuridaE]

Im new, I'm at the beginner level.. Can I simulate an AM superheterodyne receiver circuit? if yes what software is "best" to use? someone suggest to use mathlab: simulink but when i tried it, its really hard to use. Im thinking to use Multisim...

I get the idea on how superheterodyne works my problem is how to construct each circuit with a little knowledge. I googled the tube type superhet but cant find solid state superhet..

to start my project should i start with the audio amp or the rf amp?

 

[Sangoma]

First, I don't think there is much point in building each piece individually, you will probably be disappointed and put off.

If I wanted an FM receiver, I would use an MC3362 (as I have plenty) or a more modern equivalent.

For an AM receiver, something based on a couple of NE612s.

To build it with discrete components will probably not at your stage give performance you are happy with.

Make the prototype on stripboard or proto board.

Search the amateur radio sites, that is their kind of area, and you will find plenty of ideas

The kit idea is a good one, as it will give proven results.

You need to persevere with your searches, there are plenty there.

 

[unclejed613]

start with the audio amp. then build the detector stage. you will need a 455khz signal generator to test that part with the audio amplifier. then the IF amp. you will, again, need a 455khz signal generator to align and test it. then build the mixer and local oscillator stages. you will want an oscope (and possibly a frequency counter) to test the oscillator, and a signal generator to supply RF across the AM band, to test the mixer. then the RF stage, and you will need a signal generator to align the RF amp stage. to get proper tracking of the RF stage, local oscillator, and mixer,you tune the coils at the low end of the band, and tune the trimmer caps (the small screw adjustments on the tuning cap) at the high end of the band. with AM the process is fairly simple. if you have some strong local stations at the low and high ends of the AM band, you might even be able to align it without a signal generator. AM radio stations in the US are required to have their carrier frequency within 20hz of their assigned frequency (so you don't really need a frequency counter to align the local oscillator... if it's in the ballpark to begin with, you can tweak it later)

 

[YuridaE]

Uhm what is the best sotfware to simulate it?

What should be the gain of the audio amp?

 

[Sangoma]

Uhm what is the best sotfware to simulate it?

What should be the gain of the audio amp?

What's the output of the demodulator? How loud do you want it?

 

[YuridaE]

average loud should i use op-amps or bjts