This morning I had an inspiration and tried forward biasing the diode a little bit by connecting a current limited DC supply to the anode. 1ma to 20ma tried.,No luck. I was able to shift the DC level of the output up and down by doing this, but I still didn't see any envelope action.
I also changed to using a BAT41 schottky, which has a lower spec'd capacitance of 2pf.
I am thinking about winding a transformer to up the voltage coming off of the antenna. I have a few small toroid cores here somewhere. I think this is basically what biastee was suggesting.
Right now I'm still just working with stuff I have on hand. Next week I will probably order a few specialty components.
What you are seeing there is not the output of your detector, but the "parasitic" voltage induced directly into the oscilloscope's probe ground clip.
Darn it. I know better too.
I just tried making a ground wire loop and that's exactly what I've been seeing. This has invalidated all of my observations -- there could have been a subtle shift in DC level that I wouldn't have noticed.
Also, thanks for posting the W2AEW videos. I like his videos but I've never gone down the radio rabbit-hole with him before. I actually want to try making his diode-ring mixer. But before that I need to make an oscillator.
Quick fixes to improve the sensitivity:
1. add an inductor from the diode's anode to ground
2. either remove the output resistor or replace it with something in the megaOhm range.
Further refinement: match the input impedance of the diode detector.
An inductor from the anode to ground will serve as a low pass filter, correct? Am I just sizing it to start rejecting stuff above 434MHz? I think if I google "antenna matching" that I might find some stuff related to your last sentence.
As you do not have a spectrum analyzer, you can use a cheap $15 RTL-SDR dongle as a poor man's substitute for frequency range 27 MHz - 1.5 GHz or so.
I ordered one of these last week (RTL-SDR-V3) and it just came yesterday. I haven't figured out the software yet. It did come with a nifty antenna kit though.