This is the most complete and understandable explanation I have seen. All others were either too simplified so that when they skipped steps it was impossible to make connections or so complicated it would take a masters in EE to comprehend. Thank you for taking the time. Very good presentation!
Thanks for the effort you put into this. I'm just a beginner really. I understand centre tapped transformers for power supplies, but this one with the coupling capacitor conveying a.c. confuses me from the start. Is V2 produced solely from mutual inductance even though the coupling is loose? Also, is there a way to intuitively explain the phase shift without the maths? I do understand the maths fairly well, but it's difficult when coming back to a circuit like this in the future to remember that kind of explanation. Thanks!
Yes, it is for 10.7MHz. Here are the values for the components of the circuit seen @5:39 in the video: The transformer core is a BN61-202 binocular core. It has 6 windings on its primary and also 6 windings on its secondary with a center tap. Make sure that you wind the transformer the same way I did it to get loose coupling (see the video @45:44). V1, V2: 1N34 (Germanium Diodes) C1, C2: Trim capacitors 5-25pF L3: 330uH R3, R4: 68kOhm C3, C4: 820pF Cc: 10000pF (10nF) Ther is also a Transistor as an input amplifier in my circuit. It's a BF199 in a common base configuration. One pin of the primary of the transformer is connected to plus and the other pin is connected to the collector of the BF199. Cc is connected between the collector of the transistor and the center tap of the secondary. The base has a voltage divider made of two resistors to set the bias voltage. The resistor that goes from the base to the plus supply has 10kOhms the resistor that goes from the base to ground has 2.2kOhms. Since it is a common base, the base needs to be AC ground, therefore a capacitor with 10nF is connected between base and ground. The emitter has a capacitor with 2.7kOhms connected to the ground. The input signal is connected to the emitter with a 10nF capacitor in series. The supply voltage is 12V. Add filter capacitors between supply and ground. One with 10nF and one electrolytic in the µF range. To make it more convenient, I have drawn a schematic of the complete thing for you. You can find it here: www.patreon.com/posts/58257211 Have fun building and experimenting!
@@MrVideoTronix thank you very much...i have such a core often used in old TV as baloon transformer core 330/75 ohm but number of turns looks to me very small..just 6...so this is 1:1 ...hmm R3/R4 68kohm looks to me too large but ok i can try ..usualy are 10k or maximum 22k but for sure worth to try..thanks one more time ...!
Hi again ... I think that you should make video with this demodulator which present live FM stations tuning and how is produced audio ...just a friendly suggestion...
@@MrVideoTronix Hi, can I use some other values and have it working on the same 10.7MHz freq? Let's say I'd use come components that are measured by eye I mean, when you say "use small capacitators in comparison to my L2" I will use some cpacitators with capacitance 4 orders or 5 of magnitude lower than the L2
@@weweweit1156 Hi! You can use other values. The values of C3, C4, and Cc are not so critical. Cc acts as an RF short it just needs to be big enough. C3 and C4 form a filter together with R3 and R4 to remove the RF. So you can play around with R3, R4, C3, and C4 to get optimal AF output results. However, you want your transformer to be resonant with C1 and C2, so you have to pick C1 and C2 carefully and make them adjustable.
