Making a radio

[JustAnotherGuy999]

what is the minimum types of parts required to make an:
1)AM radio
2)FM radio

excluding integrated circuits of course

[Aodhan145]

http://www.electroschematics.com/tag/radio-receiver-circuits/
They will sound awful but they will work.

[JimRemington]

Google "crystal radio" for a DIY minimal AM receiver.

[German_EE]

AM Radio

1 x inductor
1 x tuning capacitor, about 350 pF
1 x germanium diode
1 x 10n capacitor
Add high impedance earphones and connectors

FM Radio

1 x TDA 7000 IC
17 x capacitor, various values
1 x 19k ohm resistor
1 x 22k ohm resistor
1 x 56nH inductor
http://www.nxp.com/documents/data_sheet/TDA7000_CNV_2.pdf

[Audioguru]

The TDA7000 has been obsolete and not made for a long time. Philips also stopped making its replacement the TDA7088 but a Chinese company makes them now and an FM "radio" with one in it is available at The Dollar Store very cheaply.

In Google you will find a few simple "super-regen" FM radios.

Simple means: Very Poor Performance and Awful Sound.

[zapta]

FM Radio

1 x TDA 7000 IC
...
http://www.nxp.com/documents/data_sheet/TDA7000_CNV_2.pdf

What is the 'noise source' at pin 3?

[Tac Eht Xilef]

FM Radio

1 x TDA 7000 IC
...
http://www.nxp.com/documents/data_sheet/TDA7000_CNV_2.pdf

What is the 'noise source' at pin 3?

Believe it or not, it's for faking 'dead air' noise when the chip auto-mutes between stations or when the detector drops out. As the datasheet says further on, the noise can be changed somewhat by fiddling the value of the capacitor on pin 3, or muting disabled by pulling pin 1 high.

edit: it's also used to blend some noise into the audio if the incoming RF signal is low (i.e. between the limiter dropping out of limit & the demodulator dropping out entirely). From memory, there's about 10 or 12dB difference between the two RF signal levels.

[uncle_bob]

Hi

Hmmm .... minimum parts ...AM radio ...

Ok, spool of wire:

Some is wound into an air core inductor
Some is wound into a free air coil pair as a speaker
Some is paired up as a capacitor or two or three.
You still need the diode ... errr ... coper oxide ... heat it up and you have a "diode"
Some to string out for a *really* long antenna (you need a lot of volts  for this beast and at uV or mV / meter .. yikes)

It's a really awful way to make a radio. You will use a monster spool of wire. It will work very poorly.

One part is about as minimum as you will get though.

Do I get a prize?

Bob (running quickly from a variety of thrown objects ...)

Now you *might* question the operation of this device. I once lived near a 50KW AM station and could quite easily light up a pilot light from their signal in to one of my long wires. I made several "interesting" radios to pick up their signal. Not all of them were *intended* to pick it up.

[zapta]

Believe it or not, it's for faking 'dead air' noise when the chip auto-mutes between stations or when the detector drops out. As the datasheet says further on, the noise can be changed somewhat by fiddling the value of the capacitor on pin 3, or muting disabled by pulling pin 1 high.

Phone companies used to do it to save bandwidth. During quite periods, they would just connect the receiving side to a noise source, being able to use the bandwidth to other calls.


As for radios, crystal radios were my first electronic projects. IIRC, all you need is a 1N34A diode, a crystal earpiece, and a very long wire, e.g. 30', acting as an antenna (connecting antenna > diode > earpiece > ground). You hear a weighted sum of all local Am stations. If you are lucky, one is stronger or closer than the others.

BTW, the crystal earpieces are so sensitive that if you rub its two wire together you can ear noise.

[MrSlack]

1N34A's are pretty overpriced at the moment. A friend of mine managed to work out how to use a 2n7000 MOSFET (incorrectly I will add!) as the detector and audio amp in one although I can't find the schematic in my notebooks now. Those are dirt cheap. Saves a germanium diode and crystal earphone price too.

[uncle_bob]

1N34A's are pretty overpriced at the moment. A friend of mine managed to work out how to use a 2n7000 MOSFET (incorrectly I will add!) as the detector and audio amp in one although I can't find the schematic in my notebooks now. Those are dirt cheap. Saves a germanium diode and crystal earphone price too.

Hi

There is a very finite stock of the stuff used to make a crystal radio back in the 1950's. Back then, indeed it was the low parts count and low cost way to do it. A lot has changed in electronics in the last 60 years ...

There are "low barrier" hot carrier diodes that make pretty good detectors. The main issue is that the packages (surface mount) are not very friendly to a first time project builder. The era of glass body small signal diodes is ... errr ... in the past.

Bob

[Zero999]

Small signal Schottky diodes in through hole packages are still cheap and widely available.

[uncle_bob]

Small signal Schottky diodes in through hole packages are still cheap and widely available.

Hi

It's the low barrier / ultra low barrier stuff that can get hard to find. They are also VERY
ESD sensitive so maybe not the best thing to recommend for a first project.

Bob