Hi folks, this time it comes to receiver again and we have built here a motherboard together the different receivers behinhaltet varieties by no means all that exist but All You Should Know here we still have the radio set down, that's just there so so you get a reference to which Period of time one should classify the whole thing because the technology that is built here is very antique In a radio today you will find everything built into an integrated circuit Most cases, even in SMD integrated circuit But we wanted you in this video simply bring the receiver technology closer times as a receiver work at all, which makes a receiver with the radio frequency How does it that out of the radio signal is language again, or music and which circuits are historically relevant if you will and that is why we have built this board here and we lead you through times time travel from the beginning of receiver technology to "Current receiver technology" as an amplifier, we have decided not to use IC amplifiers but a transistor amplifier, a so-called A / B output stage discretely build thus we also a NF from that time (audio) built amplifiers, ok now we have the detector receiver The detector receiver is historically far as I know the oldest recipient you only need a resonant circuit a diode, and in practice a high impedance headphone which can also be a crystal headphones or a headset with a coil has a very high impedance for comparison, the headset is on your smartphone turn may have an impedance of 32 ohms per speaker Headphones we have at such a detector tuned receiver have an impedance of at least 2 kilo ohms up to 100 kilo ohms ie 100,000 ohms characterized that the headphones so has a high impedance it is easier to drive him to a voltage and does not require as much power and that's exactly what a detector receiver provides a little voltage but very little current although as 600 ohms headphones work even at detector if enough level since a detector receiver as an oscillator, a resonant circuit through the resonant circuit, I can determine the reception frequency I can either adjust the coil I can now adjust the transmitter times it's getting louder but it is not entirely true because we have to adjust the capacitor So as you hear through the coil, I can adjust the or through the condenser, I now turn to the capacitor times is very loud, we need to make a little quieter So you can already see through the coil and capacitor I can determine the frequency we now have a test transmitter, the transmitter module from the other video off and have it connected here right at the entrance, so mass on mass and HF Out to the input of the detector receiver now we turn times on the coil are you listening to on, it is quieter So over coil and capacitor I can adjust the frequency is a feature from the detector receiver that we need a Germanium diode which is this weird glass diode here that are by now almost rare to have almost collector's value Now you do not need you, but "fear" that you do not get as a diode if you want to build something because you can instead use a so-called Schottky diode you can also install 1N4148 but for silicon diodes, there are two problems 1.
The silicon diode must be fast enough to demodulate the high frequency the 1N4001 or 1N4007 can not do that, of course, and 2. it has the disadvantage that it requires a much higher voltage to become conductive that is, it takes a lot more transmission power or reception level to this diode to get conductive I now put even the silicon diode on and you can hear it now, but it is very quiet compared to germanium diode, now I put it this ideal one it's ideal set So you can hear here a clear difference This is now the silicon diode here the frequency I have reinstated and now we make the germanium diode on it is much louder, much louder it is, germanium and silicon so if you've detector receiver pays attention to the diode pays attention to the resonant circuit, so you can still play a little and of course you can instead of an amplifier also connect headphones to it However, the detector receiver has the disadvantage that it is very insensitive So we move on to the next circuit the detector receiver with RF amplifier now we have the detector receiver with RF amplifier The course brings once many disadvantages because now we need a battery while the previous circuit can be passively powered by the energy transmission This circuit requires a battery we have made another change, the diode is now biased as we have now that is a silicon diode in it, is biased I take something from the battery voltage or operating voltage and forward it to the diode further characterized the diode is already conductive and it does not require the high frequency about 0.7 volts we would otherwise need that directs this diode thus the whole is very sensitive We have now the antenna no longer connected to the receiver before we tried that, we have not managed to send this antenna into the detector receiver so pure that level, by inductive coupling of the coil to said coil a signal from the speaker was audible Now, this antenna is located there and we now have, after all, good 3 cm distance from the coil and by the 2-stage RF amplifier is shown here with two transistors I can now already set the signal, and although no link is there you can hear the loud even So you can hear it very clear and how it works the high frequency pre-amplifier ensures that the signal is now being received and forwards it then through the diode and diode demodulates the whole thing again and then go here to NF amplifier or first to a driver stage and then to the power amplifier If you take a detector receiver and an RF amplifier in front of building While you need in a battery but the sensitivity is increased enormously it was now the detector receiver RF preamplifier we come to the Audion, the Audion's down here to see the yellow area a Audion is a feedback receiver that is, we have in principle an RF amplifier the at its input a Signal level from the transmitter gets but the output of the amplifier is also coupled back to the input of back is what you make now changing the supply voltage of the amplifier down as far to the amplifier by its feedback from the output to the input precisely not yet vibrates if one then feeds the high-frequency is enhanced, the high frequency and the and very good and the current branch of the high-frequency amplifier So between the positive and the amplifier can make a purely resistive if now by AM the wave goes up then we have a lot of power will fall so much tension even with this resistance and when the wave goes down or again in the negative range we have less power and it is less tension from across this resistor the result is that we have the music or speech then be able to tap on this resistance as NF, and may increase accordingly we have the whole thing already adjusted for such a Audion is very difficult for matching and we run it now times before as we turn up the volume on We hear soft music and here you can now tune in the station it is very narrowband So as a Audion can be compared in quality, with a cheap world receiver through out if you do too much feedback now then it starts to whistle if I set the frequency here now then there is indeed the point where it just goes so forth the so-called swing Bungs zero but once I go to the side of the frequency funneling it this thing can do to Use because one can build a simple receiver that receives signals such as Morse (CW) the talk is direct conversion for the frequency if, for example, now at 7.0 Mhz, a signal is and Audion to 6.9 Mhz So 6999 Mhz then you have 1 KHz difference tone, that's a nice tone Morse the then you hear so we could now key the radio, so you call it, and turn from then one would hear this whistling sound the Audion has the advantage that it has a very good selectivity and high sensitivity but has the disadvantage that it is very difficult when it comes to the match there are other circuits, you just can in principle take an oscillator and turn potentiometer before the resonant circuit, the high frequency you feed then needs to which receive in the case we have here again this inductive coupling from the transmitter to the receiver coil then you can just build a recipient from an oscillator easily is very convenient, it is also very antique you can also demodulate SSB then you can also single sideband modulation received so but that's really been a skill exercise that right set OK, that's it for Audion now we have again has a 3-stage RF preamplifier output on a detector receiver actually the whole thing is a superheterodyne circuit but since we wish to merge little by little in the superheterodyne technique since just yet is a fairly large chunk of information we are going the whole time slowly ye have foreseen this two-stage RF amplifier who already had a very good reception power now we have placed one better and have built a transistor to the reception performance would like to enlarge we have actually a superheterodyne but we have a little trickery the IF transformer, to which we come later, we have manipulated that it allows various frequencies and the IF filter we have manipulated but that it can not only the 455 Khz by other frequencies happen now relatively well can the result is that the sensitivity has increased dramatically as we previously had to move here quite close to the coil we can now at a distance of a few cm well twice the range Send our music wirelessly to the receiver while the receiving frequency is set by this Dreko now I show times how good this IF filter attenuates when you turn him Now I turn these 455 Khz filter back to it is heard only very softly because the transformer is not filtered here and we just have so much RF level that it goes through So as you can see, a three-stage amplifier Hf is definitely more sensitive than a two stage Now you might say, why do not we four stages then you could probably already hold out so instead so no, that's easy if you have 4 steps captures the whole thing at some point swing that is, the receiver is so sensitive that the signal I back is perhaps radiated anywhere in the conductor track forward again goes in to the antenna and why do you do that just as actually we have done so because we want to testify unto you what happens when you not make a transistor to But in a broader sense, we are now building piece by piece a superheterodyne on the superheterodyne is the next clip Now we build a simple superheterodyne a superhet operates according to the principle of frequency mixing while the receivers we have here, the detector receiver are detector receiver with RF preamplifier and Audion so-called straight receiver which means that they receive the frequency to adjusting the resonant circuit a so-called superheterodyne operates according to the superposition principle the superheterodyne takes each frequency which one wishes to receive and mix them to a fixed frequency herrunter in the case of 455 kHz, the so-called intermediate or IF frequency To ensure this, we need quite a lot of components Of course we need from our previously input amplifier providing a signal on the so-called mixer the mixer now receives a signal from the so-called local oscillator What is a local oscillator? Now if we take the radio now and set an arbitrary frequency here and turn on the local oscillator, here you can adjust the frequency again by a coil which is adjustable or which is adjustable by a capacitor when I turn now at least it would somehow go I agree I have here a signal so I can here set the and have here a signal, so it's just the way from the transmitter section generates an oscillator signal of a this signal, we can do that while the speaker is on then you hear that there is doing what I pair now on my mixer now here ever silence since missing namely still some what is happening now, we now have here a signal and give it to the mixer but have no filtering clear now that silence is because we do not send a carrier and in that we will send no carrier can be heard just nothing but now I'm over here, building a ZF filter and insert the time to already it has become quieter, the noise and now I need more clips, I have to see to see even more clips are, ah, I have here a now I take another Klip, switch the transformer to since then happening in theory what, but it does not work as well as I wish it that it works it works a bit This transformer can already now 455 Khz happen strengthened while it filters out everything other stuff and here we can again pass through a filter of 455 Khz now we have our superheterodyne, a simple superheterodyne already so far assembled what we will remember now is when we come here in the vicinity we hear it only very softly if we but now synchronize the local oscillator properly we can adjust it So through the coil, I can adjust it or by Dreko Now the superheterodyne is now not much better than the straight receiver But the farther we build these superheterodyne the more we are why you used the superheterodyne in practice understand so if I with the coil times then go we hear the music known too loud…
Now we have a problem with the superheterodyne Now if I have a weak signal then you can hear it really well So here you can hear the great music Eflose if I but with the coil of the transmitter closer to go to the coil from the receiver back then it will distort some point, it will only louder so it klijngt no longer good it distorts total what are we doing now? the problem we have here now, we have the Detector receiver is not as strong as it is just really loud but at the detector receivers with RF amplifiers we have the and the Audion we must then turn to the pot again and just for stations that fluctuate, so by overreach the field strength varies, it is always very annoying and very annoying when you have to turn increasingly to the Poti permanently it is loud, it is whistled again so it is not used in practice so now we need a few more clips Yes, we had a little bit better vorbeiteiten should Super, 2 clips, ok, now we have a circuit at this electronics off here we now have the 455 Khz ZF for detector receiver because if you watch the times, here again we have a diode which I have unfortunately forgotten draw in here is a diode detector in the receiver as the newly demodulates the but now we have 455 Khz here that I can now give a so-called AGC circuit The first thing the AGC circuit is now first makes they kuckt, I have absolutely a signal observed the green LED is just not very bright So the LED observed when you were making a signal now if I with the Transmitter to antenna go then getting the LED lights up that is, that we have a certain signal strength, which is like the radio up here this Tune LED But now we still have the problem that if we go too close it does not sound good, the LED says but we have a very strong signal what can I do with this information now? an LED or an electronic circuit tells me we have a signal or if we have no signal and she goes on to say, which is determined by this capacitor here We have a strong signal or we have a weak signal Now I can go forth now easy and can with the Singal we have here, from the LED or the transistor is yes, a changing resistance, with this transistor, can I control the preamplifier here now this is so when I would go now here and would say, okay, now it's too strong then I'll go so far away, now it's only that it is now not I do, because I can not influence so now how strong the transmitter goes forth I would have to change every time the antenna length, which is not suitable for practice but I let make the so-called AGC now AGC stands for Automatic Gain Control I have to do better AGC stands for Automatic Gain Control Automatic Gain Control and I include the output from the AGC control to the input of my RF preamplifier As long as there now is not a strong signal since this amplifier is running at maximum gain as well as he can only strengthen But now when the signal is too strong when the signal is too strong then the AGC adjusts back whom I put now times from So here you can hear it quite well now it distorted now it does not distort with AGC So without AGC it distorts and AGC it sounds good and which is now a superheterodyne as how to use it because now you can here with a variable capacitor, or in the case a trimmer capacitor Setting your frequency of the transmitter you do not care how great the level of the transmitter, which is all controlled automatically and you can just listen to the station this effect we have heard before that it distorted the one had, especially at the detector receivers with RF amplifiers and the Audion we could have problems, and therefore, also for other reasons better selectivity, excellent reception performance therefore used in such a radio a superheterodyne then there is something nasty that we have now perhaps if we could get for presentations, I am now but not sure it down due to the frequency at which we send there are the so-called image frequency that is to say that it may be that a transmitter 2 times it receives of course that is annoying but in a simple superheterodyne this is an effect of that is now I look at times if I can receive the 2 times I'm not sure if I can get it to me back, probably not extending receives probably just somehow even So unfortunately it's not because the Local oscillator no area covers large enough but theoretically could be the transmitter 2 receiving times and this is the so-called mirror frequency which can be suppressed in that one makes a double superheterodyne So virtually copies the circuit namely, local oscillator input amplifier the one takes then somewhere else, and mixer and then I, for example, shortwave I mix first on a frequency for example, 1 MHz and 1 MHz I mix then again down to the 455 Khz then I have the effect not as strong some he might still there but very strongly suppressed but as I said, for reasons of space and time constraints, we have here no longer get up that's just the superheterodyne, the circuit finds her in such radios in basic circuit it was now so broadly on the subject RF receiver technology later we stayed very long, the Eflose has bothered in the garden to stretch a nice antenna and we still have a few clips for you such as these recipients then behave in reality to a real antenna ok, thanks for watching and a thumbs up, say already now, we would be very happy