AM Medium Wave Radio Receiver Design.
First of all, I am a hobbyist and stuff related to electronics are not very strange to me but the chapter of Radio and RF frequency , intermediate frequencies , resonance are haunting me since I got myself indulged in this project.
My goal is to design a very simple Medium Wave Radio receiver that should not use any kinds of ICs ,IF Transformers or complex components. Only a few inductors , loopstick (found from an old broken radio) , trimmer , ceramic capacitors , transistors (BC547) and resistors are to be used.
The radio should play all the channels from 500 KHz to 2 MHz (legitimate medium wave broadcasting frequency in my country).
So I browsed through the internet and found some schematics.
This was the first radio circuit that I tried to work with. But without any productive result. Neither did the creator of this diagram mention the number of turns nor the wire diameter nor the solenoid diameter and nor the coil length.Now lets head to the second schematic.
This one didn't seem to work either! The creator mentioned number of turns only without mentioning diameter of wire and diameter of solenoid and coil length. Now lets have a look at the last circuit I which tried.
I found the last circuit from a YouTube Channel. Same as the 2nd circuit, the creator forgot to share details about wire diameter and solenoid diameter and coil length. Neither did it appear to be working at all!
The loopstick has 2 coils. Yellow one is the longer coil and the Red one is the shorter. I did not make any changes in coil turns or coil diameter while using this loopstick in my DIY circuit, I just cannibalised this loopstick antenna wholly and connected the two terminals of my gang condender to the longer (Yellow) coil accordingly and then I tried to get the input from the shorter (Red) wire by connecting one end to emitter and another end to the base of the first RF amplifying transistor (Circuit No 3).
I connected the 4 individual capacitors in the gang in parallel to get a total capacitance of almost almost 320pf (C1 + C2 + C3 + C4) while the small green wire in the middle of the gang joins the ground of both FM and AM side. That can be seen in the image of gang I referred above with a hyperlink.
Not much adequate information is given on the internet about the loopstick in Radios. In some circuits, they mention the number of turns but they forget to mention the diameter of the wire and the diameter of the solenoid on which it is turned that makes it harder to figure the inductance out.
I am willing to develop a heterodyne radio without using IF transformers. Although IF transformers are completely out of market, I have only two IF transformers which were pulled out of that old radio circuit, some of the legs of those transformers got broken. Still, I would prefer a heterodyne schematic with no IF transformers.
Points to be noted...
- I powered all 3 circuits with a 9 volt battery.
- While tuning, the speaker is only making random "clicking" sound , that too very timidly. Nothing else.
- In circuit 2 and 3, 1N4148 diodes have been used for rectification purposes because I dont have germanium ones right now.
Now, are there any problem those circuits? Or it is my faulty design which is making the resonance weak? The nearest Medium Wave Broadcaster is almost 250 Kilometers (155 miles) away from me.
I am stuck in this project and cant find a way out but still have the wish to complete it desperately! So I would like to hear some tips from the experts in this community for the betterment of my project. A working circuit diagram will even be better for me to understand the things properly.