wow that’s amazing !!! I wished I would understand all that!!!
http://m.youtube.com/watch?v=3Zzmi_Kno4 … e%3Dfvwrel
I was wondering why he didn’t connect anything
to the inverting input of the op amp…
I always thought that when an input is not used
it should be at least grounded!
I hope some day I will be able to build a radio
with an op amp like that and understand the underlying
theory behind it … :oops:
It is a simple crystal radio (3 components) connected to an op amp audio amplifier (4 components), plus an antenna wire, a speaker and a battery. Google “crystal radio” for a very large number of similar circuits.
Yep crystal radio. Back in the '60s my brother and I would build these from scratch:
wind the coil on an oatmeal box (the round one).
make a variable cap with aluminum foil and plastic wrap
use various quartz, fools gold and other rocks with a thin wire to make a diode (cat’s whisker).
Then an ear phone from a transistor radio to hear the radio stations.
Lots of fun.
Hi, guys… You guys are very smart. I am new to this electronics stuff. As much as it all seems fun and all… there’s a lot of underlying theory in there for a guy like me, for example, how would I know the thickness of the wire, the amount of turns for the wire, the theory behind selecting the right capacitor and inductor so you can receive a particular frequency and lots more…
I would love to buy a kit that not only shows how to build a radio like that, but with all the applied theory and mathematical equations would be nice 
I looked around and I saw kits that show this, but I am afraid to buy them because I may be disappointed due to the lack of theory they may miss out on. The nice things about electronics is not only to be able to build a circuit, but to also fully understand it. And that’s why I am afraid to buy certain kits 8)
Anyways … thanks for replying…
For learning how radio stuff works the “ARRL Handbook” is pretty good. There are many used copies around so you can get one at a good price.
It covers most radio theory well. It also has equations to calculate LC vales for a frequency and tables to determine size and number of turns to make coils of a know inductance.
Us smart! Maybe, but really we just have been doing this a longer time.
thanks for your kind words waltr…
the truth is I am slower than others… lol
thanks for the handbook … looks like a pretty complete
reference …
