# Learning electronics with radio, how does this work?

#### MarkSimms

Joined Apr 6, 2016
54
I know I'm asking noobie questions I should already know, but without a teacher I'm in need of correct answers. Ive looked at a few single transistor radio circuits and they all seem to have a tank circuit feeding the collector of an NPN transistor, with a capacitor to bypass the transistor collector emitter altogether, I'm assuming this is the tuner, but how does it work, can DC voltage and AC voltage both exist while the tank circuit has DC voltage applied to it?

also how do you demodulate FM, I can see a diode in an AM circuit just cuts it in half, but hows FM or SW demodulated?

#### MrChips

Joined Oct 2, 2009
29,211
As someone on AAC already quoted, "Ask a simple question and appear a fool, don't ask and remain a fool".

Without seeing a circuit schematic of the tank circuit it would be difficult to make a comment. In general, yes, DC and AC can exist simultaneously in any circuit. Think of every signal as being AC, meaning it has frequency content. DC simply means that the frequency content is at 0Hz. You can have a signal of 10VDC and an AC content of 1V peak-to-peak. This can still be considered as DC + AC.

On your radio dial, AM means amplitude modulation while FM means Frequency Modulation.
Usually the AM band is also known as MW or Medium Wave which is from 500 to 1600kHz.

FM broadcast band is 74-108 MHz dependent on country.

I will assume that SW you mention refers to Short Wave band which could be 1-50MHz generally speaking.

AM and FM can apply to any frequency band including SW. Most radio transmissions on SW use AM.

A simple diode can be used to detect AM signals.

FM demodulation requires more complex circuitry. A commonly used technique is called phase locked loop (PLL) which is simply an oscillator circuit that locks on to the phase of the RF signal.

#### MarkSimms

Joined Apr 6, 2016
54
Thankyou, "AM and FM can apply to any frequency band including SW. Most radio transmissions on SW use AM" is a great piece of info, means I can use a simple aerial to tune in on SW.

#### MarkSimms

Joined Apr 6, 2016
54
thank Bertus looking at that now

#### bertus

Joined Apr 5, 2008
22,217
Hello,

Radio stations in the SW bands are mostly AM modulated.
Ham radio station in the radio amateur bands, wich are can be found in the SW range, are mostly SSB modulated.

There are also a lot of SDR (software defined radio) sites on the internet:
http://websdr.org/
On those sites you can listen to a lot of stations all around the world from your PC or laptop.

Bertus

#### MarkSimms

Joined Apr 6, 2016
54
I'm going to be the most appearing fool going, but I have to ask, is an areal or antenna using one or two wires? what I'm saying is a coax has core and shielding wires, I can only visualise a current between 2 wires like AC from a music player into headphones, but I'm thinking I'm wrong and radio waves are picked up on one wire then travel to ground?

#### MarkSimms

Joined Apr 6, 2016
54
Bertus I found that site last night and it blew me away how good it was, but I was wondering if there relaying the whole analoge spectrum, because that would be a lot of data and white noise too?

#### ISB123

Joined May 21, 2014
1,236
All analog circuits will have noise.Its up to you to remove as much as possible. Look for Bob Pease tutorials he was analog circuit legend

#### MarkSimms

Joined Apr 6, 2016
54
thanks Bertus, its all very interesting stuff.

#### MarkSimms

Joined Apr 6, 2016
54
ISB123 your mistaking me for being clever, I'm asking is an areal one wire? or are the radio signals received on two wires? I think one then they travel to ground, but I don't know for sure, as I say I'm a noobie.

#### bertus

Joined Apr 5, 2008
22,217
Hello,

The size and shape of the antenna can be different.
Have a look at the links of the following page:
http://ac6v.com/antprojects.htm

It shows a lot of theory and practical articles.

Bertus

#### ISB123

Joined May 21, 2014
1,236
ISB123 your mistaking me for being clever, I'm asking is an areal one wire? or are the radio signals received on two wires? I think one then they travel to ground, but I don't know for sure, as I say I'm a noobie.
Radios don't use directional antennas since we have no idea from where the transmission is coming. Size of antenna dictates at what frequency it will work. For radios you will need omnidirectional antenna.

#### MarkSimms

Joined Apr 6, 2016
54
Bertus I just learned already, that the areal needs to be insulated from ground , great reading this site thx

#### Papabravo

Joined Feb 24, 2006
20,383
Radios don't use directional antennas since we have no idea from where the transmission is coming. Size of antenna dictates at what frequency it will work. For radios you will need omnidirectional antenna.
This is not strictly true. A receive only station can greatly benefit from a directional antenna. For two way point-to-point communication, a directional antenna is essential. Multi-element TV antennas are highly directional and many people mount them on rotors. To get started you just need a long wire from a window to a nearby tree. It can be any convenient length, and it will pick up some things. As your needs change so can your antennas.