2n7000 lab - night two, no smoke

I decided to revist the experiement from last night. Since I let the smoke out of the parts last night I wanted to see if I could reproduce similar results (power levels) and maybe try tweaking a few things.



The initial schematic is similar to last night except that 100uH molded inductor was replaced with a 7.5uH inductor made with a toriod. (FT50-43 with 4 turns) That has a Z=476 @ 10MHz which seemed more realistic.


I then measured the power output for 1 FET and then reran the test with 2 FETs. I experimented with several different variations of broadband transformers to try to find a better impedence match... it had very little impact on the power level so I left it out.

Two realizations:
1. I am consuming less current than last night. (Why?)
2. I am generating less power/gain than last night.  (Why?)



Using my old oscope I tried to look at the waveform to see if I could tell what class the amp is running in. Frankly I can't tell. It looks sort of like class E or just a really ugly class C. --Hmmm... something to research.


Two variables from last night:
1. New FETs (I let the smoke out of the 2N7000 from last night)
2. The inductor is different (I let the smoke of the 100uH inductor last night)

I don't know if I had some awesome parts last night, a flaw in the test, something to do with the inductor, or some other wild card.    Last night consumed 4x the current and generated another 8.31dB.

I don't think that I am turning on the FET enough with just 10dBm of RF drive. I might need to look at biasing the gate a bit. That is an experiment for another night.

PS... I did some testing a few days later. I think that I am running into a couple of issues.

1. Some variablility differences between parts. (They are not RF/HF rated parts.)
2. The low output impedence without a matching circuit is causing the parts to fail in some cases immediately.

--I tried about 10-12 different parts and most of them were failing and had low gain values. Once I added an transformer to out the output I was getting HUGE amounts of gain (16-20db) but the efficancy was low because I was running in the class A-->C range not class E. At one point I had 400mW with 0dBm of drive at 10MHz.  I will retest this new scenario and likely post it on the blog once I have some better info.

73 de NG0R