[Music] the super head radio is a form of radio technology or technique that has dominated the radio market for nearly 100 years everything from domestic broadcast radios to professional communications equipment and lots more all of these have used the super head or super heterodyne radio for many years in this video we're going to look at what the super het radio is how it works and then move on to see how radio receiver technology is advancing the first question to ask is what actually is a super head radio and what is its basic concept in a super hat radio the radio signal is changed from its received frequency to a lower frequency before it's detected to see how this happens the block diagram of the most basic super head radio can be seen here basically the signals enter the rf amplifier and tuning stages where they're amplified and some broad tuning is provided then along with a signal from an internal local oscillator they enter a mixer where they're converted to a fixed frequency section known as the intermediate frequency or if in this section they are amplified and the majority of the selectivity is provided and this removes signals from adjacent channels finally the signals are demodulated and the resulting audio is amplified and passed to headphones or a loudspeaker or used in whatever way is needed however let's look at the individual stages in more detail to see how they work and what they do the key circuit block is a mixer or as it is also known a multiplier the concept of the super hat is to do use a mixer and a local oscillator to down convert the signal to a lower frequency where it can be more easily processed and filtered it's worth taking a little time to look at what a mixer is and how it works a mixer is an electronic circuit in which two signals enter and they're multiplied together the instantaneous voltage on each of the inputs is multiplied to give an output that's the product of the two inputs the result of this is that signals with frequencies equal to the sum and difference of the two inputs are generated to explain this a little further let's take the example where there are two signals entering a mixer one at a frequency of one megahertz and the other at a frequency of 1.5 megahertz as we mentioned before there will be two additional signals generated one at the difference frequency of 1.5 minus 1 megahertz which is 0.5 megahertz and the other at a frequency which is equal to the sum of the two input frequencies in other words at 1.5 plus 1 megahertz which is 2.5 megahertz now let's see how this can be used within a radio receiver to mix a signal down to a fixed intermediate frequency taking the figures we used before let's say the local oscillator is running at 1.5 megahertz and the incoming radio signal is at one megahertz as before we see that two new signals appear on the output of the mixer one at 0.5 megahertz and the other at 2.5 megahertz if we make a fixed frequency filter at a frequency of 0.5 megahertz to fit on the output of the mixer then only the signal at half a megahertz will pass through at this point we can note that the difference between the signal and the local oscillator must be equal to that of the intermediate frequency or if filter in this case it must be 0.5 megahertz the next issue is how to tune the receiver this is actually quite simple let's see what happens if the local oscillator is shifted up to 1.6 megahertz now we can see that a signal at 1.1 megahertz will produce signals at 0.5 and 2.7 megahertz again only the signal at 0.5 megahertz passes through the filter so to tune the receiver all we need to do is vary the local oscillator the next thing to think about is what is called the image response within the radio the image in a super head receiver is when you down convert you're actually receiving both the upper sideband and the lower sideband which are offset by the difference between the input signal and the local oscillator so you end up with these image frequencies that can cause interference because a an interfering signal will be mixed right on top of your desired signal the image signal is a critical issue within the radio let's again take the example where we have our incoming signal at 1.0 megahertz and with the local oscillator set to 1.5 megs when these two signals enter the mixer they produce an output of 0.5 megahertz as we saw before however there's another signal that can also produce an output at this frequency if we have a signal at 2.0 megs this will also produce an output at 0.5 megahertz when mixed with the local oscillator so we have two signals that can enter the intermediate frequency stage one at one point naught megahertz and the other at 2.0 megahertz here the unwanted signal is called the image signal the unwanted image signal must be removed otherwise it'll give rise to interference to remove it a tuned circuit is added before the mixer to only accept the wanted signal normally an amplifier is also included to provide some gain before the mixer when tuning the receiver the local oscillator and the rf tuning must move together or track as it's called this was achieved in early radios by having a twin gang variable tuning capacitor modern radios will use electronic forms of tuning but these must still track together the next area to take a look at is the intermediate frequency section function of the intermediate frequency is to be the place where most of the gain of the radio is placed and also the intermediate frequency is typically a an amplifier of defined bandwidth which sets the receiving bandwidth of the radio so for example for an fm radio the bandwidth would would be about 250 kilohertz and that's defined by filters in the intermediate frequency the reason for having the if on a fixed frequency is because it's possible to make very high performance filters in this way it's in this section of the radio that the selectivity to reject signals on adjacent channels or frequencies is included older radios use tuned interstage coupling transformers and this was normally good enough for broadcast reception it's also possible to use ceramic filters or in cases where high levels of selectivity are needed then crystal filters may be used the iaf is also the area that provides the majority of the gain of the radio so often two or three stages may be used once the signals have been filtered and amplified in the iaf they are demodulated to recover the baseband information such as the audio from the signal different demodulators may be used according to the type of signal being received am ssb fm and so forth the recovered signal is then typically amplified and passed to a loud speaker or headphones although it can be used in other ways as required the super head radio has come a long way in its history and its technology is still developing modern super hits use digital processing techniques originally it was at audio frequencies but as technology's improved it's moved to if frequencies and that is also used for demodulation and filtering the development of digital signal processing technology is still moving forward and new technologies like software defined radio are taking over the super head though is still widely used and over many years since its invention it has given great service for more information about the super het radio and other topics check out the links in the description below you can also subscribe to the channel and don't forget to like the video please [Music]