Hello,

I moved your thread to the "radio and communications" forum.
Did you notice this thread, that I started a long time ago?
RF related links

The link to the books I gave you is also from this thread.

Bertus

 

Hello,

On youtube I found this old video about AM and FM:

Bertus

 

Antenna Basics

@MarkSimms
We have gone from discussing AM, FM, MW, SW to antenna basics.

Before we get too far ahead, you may want to consider why we use the terms
LW - long wave
MW - medium wave
SW - short wave

These terms refer to the length of the wave which is related to the frequency and the fundamental speed of light:

λ = c/f

where,
λ = wavelength in metres
f = frequency in Hz
c = speed of light = 3×10^8 metres per second

In general terms,
LW is about 30-300kHz which works out to about 10km - 1km wavelength
MW is about 300-3000kHz which works out to about 1000m -100m wavelength
SW is about 3-30MHz which works out to about 100m-10m wavelength

A straight wire antenna is the simplest antenna you can make. For optimum performance you want the antenna length to match the wavelength of the RF signal or multiple lengths of the RF signal. Reading up on antenna construction you will find instructions on how to create antennas that are ¼ wavelength and ½ wavelength dimensions. For an antenna tuned to exact wavelengths you also have to apply a correction factor to compensate for end effects.

For basic SW reception, a simple long horizontal wire as long as practical works quite well. Having a good connection to earth is also a good thing to have.

 

Hello,

As MrChips told you, the size of the antenna is dependend on the used frequency.
If you do not have the space to have a large receiving antenna, you can go for an active antenna.
Most times this is a small antenna with an amplifier.
This page will give you some links to these active antannas:
http://www.dxzone.com/catalog/Antennas/Active/

Bertus

 

thanks guys, I did not see this thread before.

 

how do I demodulate SSB, I'm hopeing long term to create simple radios to pickup ham radio? maybe its beyond me, crystal set tank circuit took me time to understand

 

MrChips thanks for the definitions

 

Whoa! You're running too fast for us to keep up with you.
Let's stick with simple AM for know.

SSB on SW is usually AM.

When you Amplitude Modulate (AM) a radio frequency (RF) carrier, you end up with three signals.
One at the carrier frequency, one below the carrier frequency and one above the carrier frequency, the last two are called the side bands.

Here is a simple example.

Let us assume the RF carrier is 500kHz and we want to transmit a 1kHz tone using AM.
We end up with three signals, 499kHz, 500kHz and 501kHz.

All the useful audio information is contained in the side bands, i.e. at 499kHz and 501kHz.

SSB, Single Side Band, means that we can save transmitter energy by simply transmitting only one of the side bands and eliminate the other side band as well as the carrier.

To receive SSB signal we simply add back the carrier at the RF frequency at the receiver using an oscillator called beat frequency oscillator (BFO).

 

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.

Tell that to the satellite antennas you see everywhere. Having high directionality is essential if you want to send a few megabytes per second to a receiver 25,000 miles away using only a watt of transmit power.

If you know where the signal is coming from or going to (and this is very often the case), then using a directional antenna is high beneficial.

There are, of course, many situations in which you don't have that information and so you do need to use an omnidirectional antenna (or scan a directional antenna).

 

I was talking about FM radio especially portable one.

 

MrChips the help understaning SSB is helpful, but I may be asking a silly question here but why cant the SSB transmission just go straight to an amplifier and output to a speaker, as I see is the SSB is an AC signal above 0v or an AC signal below 0v I don't know wich one is used up or down, but why do I need an oscillator ? I need simple to understand methods for my first radio, so can I do it without an oscillator, byy just using a diode? and can I tune into to SSB with a coil and capacitor like a crystal set? I know I'm asking a lot of help.

 

Hello,

Here is some info on receiving SSB signals:
http://www.electronics-radio.com/articles/radio/modulation/single-sideband-ssb-basics.php
When you are using a superhet receiver, you can make a BFO on the MF frequency of the receiver.
http://www.flashwebhost.com/circuit/ham_radio_bfo.php

Bertus

 

Bertus , that's perfect! thankyou for links

 

Hello,

The pages 63 to 66 of the following PDF might interest you:
fakta55.pdf

Bertus

 

I've got plenty now to be figuring out now, thankyou that indian receiver is very interesting thx

 

OMG, this means you can use a crystal set, with a separate BFO nearby to hear ham radio, and the SSB is AM so the crystal set can be used and amped up, thanks guys

 

Hello,

Yes, you can.
The BFO will generate the missing carrier.
The frequency of the BFO must be at the frequency to be received.

You might also want to have a look at the direct conversion receiver:
https://en.wikipedia.org/wiki/Direct-conversion_receiver
Here is a project that will build a direct conversion receiver:
https://aa7ee.wordpress.com/tag/direct-conversion-receiver/

Bertus

 

Hi Mark. SW listening has really changed over the years, especially with Digital Signal Processing.

It is now possible to take an antenna, and connect it to a digital switch. If we turn that switch on and off the the proper manner,(with an I/Q oscillator) and then feed the output of that switch to your aux audio input to your computer, you can not only listen to the station, you can watch the sidebands as your listen. When you can see those sidebands, it really helps understanding. How would you like that?

It's called Software Defined Radio. SDR radio. You can try this out very cheaply with a TV dongle.

Search google for sdr dongle to see what I'm talkin about. I've had my dongle for about 4 years and its great.

Search google for sdr radio for to see commercial and ham gear.

If you would like to home brew, search google for tayloe mixer.

And if that doesn't strike your fancy, and you like microprocessors, then ADC sdr radio is the way to go.

Check it out.

 

I have a TV card in an old broken PC, I will look into it. sounds like lots of fun. I found wedsdr.org a mesmerising moment.

 

Hello,

Here is a page with the use of a DVB-T stick as @BR-549 mentioned:
http://www.epanorama.net/newepa/2013/10/23/software-defined-radio-with-usb-dvb-t-stick/

Bertus