Hi guys (and gals), I hope all you Hams won=92t laugh at me too much.
So as a final piece to my current project we want to make an AM radio receiver. (This is mostly to give a =91real world=92 mixing application.) Now the only AM radio I=92ve played with was a long piece of wire as antenna to coil, variable cap, Ge diode to ear bud. The current idea is to NOT do the frequency selection with an LC circuit but with a mixer. So, antenna to HF amp to mixer to audio amp. I banged this together yesterday and it worked OK, but far from great. I was able to see some nice ~10kHz wide side bands around a central carrier. (on a spectrum analyzer) But when I tuned the LO to be centered on the carrier and listened to the sound it was disappointing. The sound level was bouncing around at about a 1 Hertz rate. I could see the same thing on the =91scope, the HF signal from the antenna was bouncing around.
My antenna was just a piece of wire maybe three meters long stuffed into the BNC jack of an amp with a 1 kohm input impedance. My first thought was that I need some sort of balun transformer on the input. (I=92m guessing the bouncing around of the input was because the other half of my antenna was ground?)
This then raises several questions. What=92s the impedance of my piece of wire. (I=92ve got to keep the transformer impedance well above this.)
OK I=92ve got several more questions, like should I use some other sort of antenna. But I=92ll wait...perhaps my first assumption is wrong!
Thanks for any advice. (discrete chuckling from Hams is OK.)
George H.