Hello,
To preface this I should say I do not have any real experience in radio, so I don't doubt I'm making a simple mistake.
I am working through the book "Learning the Art of Electronics" and am on lab number 3L.4, designing an AM radio receiver. This is a design exercise and therefore there isn't a schematic exactly but it does lay out the building blocks and gives oscilloscope screenshots of what to expect after each stage in the detector. The circuit blocks are a 30' piece of wire as an antenna going directly into a LC resonant circuit tuned for an AM station (I chose 1500kHz to match a fairly local station), then rectify that signal through a schottky diode to a leaky peak detector to yield an audio frequency signal.
My circuit takes the antenna directly into a parallel LC circuit, with a 10nH chip inductor and a 1uF ceramic capacitor (which I believe should resonate at 1590kHz theoretically). I have the circuit built with a 1N5817 diode rectifying that signal into a parallel RC 'leaky peak detector' of 1nF and 30k
, but I am not even getting anything resembling the sample screenshots shown in the book at the LC point. My screenshot is attached. The book shows a very distinct AM signal with a 1Vpp amplitude at this point...I assume my problem lies here.
I tried a different resonant frequency by adding a second 1uF cap in parallel with the first to lower the resonant point to 1130kHz since I also have a fairly strong signal on 1120kHz here, but no difference. I have attached a photo of my construction (ignore the L and C being in series in this photo, I was just experimenting). I also disconnected the diode just to see if the LC circuit would resonate by itself, it did not. All that said, I can get a signal to couple into the antenna from my function generator but the amplitude at the LC point is just 100mVpp.
I was able to build and test the resonant circuits earlier in this chapter, in which I used a 10mH toroidal inductor and a 10nF ceramic disk capacitor to resonate around 16kHz. When I built this new circuit with the 10nH chip inductor and 1 or 2uF ceramic SMD capacitor is there some detail I am ignoring that is preventing it from resonating?
Any insights would be appreciated!
- Jon