By: Comments Off

Class E experiments for a Sunday evening

Once my family went to bed I started working on another prototype.

In this version I used the ClassE software from TonneSoftware to try to determine the proper values.

I used a variable cap for the shut capacitor so that I could try to tune the circuit a bit. The C2L2 tuned circuit had some challenging values so I had to get creative with the capacitors and the inductor was 33 turns on a T50 core. (I probably should have used magnet wire... but it worked ok as-is)

When I first tuned up the circuit it was clear that 10dBm was not enough drive to effectively turn on the FET as a switch. I add a voltage divider to the gate of the FET which improved the performance quite a bit. (A variable resistor would have been a better way to tweak the bias of the FET.)

10dBm of drive + ~1.7vdc gate bias + 13.5vdc supply voltage = ~160mW (boring)
10dBm of drive + ~2.5vdc gate bias + 19.5vdc supply voltage = ~1W (Interesting)


Here is the oscope image with 19.5vdc of supply voltage. The top (channel 1) is the input and the bottom (channel 2) is output with no additional filtering.

 

Observations:

  • While 1 watt is interesting it did not meet my goal. I had to use 19.5 volts and my goal was 13.5 volts.
  • The gate voltage is going to require more investigation.  I would like to find a no-tune option using standard value parts if possible. (2 volts looks to be approximate the gate voltage I need to target)
  • Running 1W the FET was warm but did not burn my skin. I suspect that I am not getting the proper turn-on and turn-off for the proper Class E efficiency that I should expect.
  • The current draw seemed to be ok (it could be better) for what will hopefully become a portal CW radio.
  • I am not getting the gain that I am exepcting but I am not sure why.
  • I took an hour to build this prototype and the blog entry took almost as long.  :-)

73 de NG0R

By: Comments Off

Class E Amp - Searching for the holy grail

I spent some time at work bench again this afternoon exploring how a Class E amplifier might work.

I started off by using a Dan Tayloe N7VE example of a "No Tune Class E" amplifier. I tweaked a couple of things for parts that I have on hand but the design is about 90% the same as what is in his presentation.

In my testing I am using a signal generator as my source and then sending the output to a directional coupler with a -20dB port for my microwatt meter and the other port into a dummy load. I am also using a my two channel digital oscope to be able to watch the before and after waveforms. In this testing I am not concerned about bandpass or lowpass filters since this is a prototype that will be talking to a dummy load. (In the real world it would need to be filtered since it is going to have harmonics that are in excess of the legal limit.)

Initially I did not bias the gate but I found that I did not have enough "drive" to turn on the 2N7000 effectively. The idea of the Class E amp is the FET is operating a switch, on or off in a semi-square wave pattern. The drain capacitor labeled C1 is supposed to be helping to charge and discharge and make the switch turn-on hard and then turn-off again.

In a tuned Class E amp L2 & C2 are a tuned circuit to create a fly wheel effect. In this "No Tune" example we are giving up efficiency/power since we want to tune across seveal bands.

I was able to get some gain but not nearly what I was expecting. Since I am pretty early into the testing and learning process this is an incremental step. It was interesting to see how the wave form changed and when the phase started to shift. When you reach full Class E mode the input and output sine wave will be out of phase. 

The images below were captured about 15 minutes before the data table (above) was created so the numbers maybe slightly different. The images from the scope are specific to ham bands since that was my area of interest. (The freq counter on the scope is close but not the exact frequency of the signal generator.)

 

I have a couple of other ideas in schematic form on paper at my desk. I am going to try to build a couple more prototypes and see how they perform. I might need to work on something band specific before I try to work out the wind band aspect of this.

I would like to be able to cover 40m, 30m, 20m, and 17m. I think that higher bands like 20m and 17m are going to be a challenge without a band specific C2 + L2 combination or a different FET.   I also need to look at this on my spectrum analyzer to see how the harmonics are looking.

Here are a couple of interesting links:
http://www.vk2zay.net/calculators/?body=class-E.php

http://www.classeradio.com/

http://www.alan.melia.btinternet.co.uk/classepa.htm

http://www.wa0itp.com/class%20e%20design.html

http://tonnesoftware.com/classe.html

73 de NG0R

By: Comments Off

Bread Notes (Baking)

I was working on making bread tonight with my son and thought that I should update my notes on the blog so that I can get to them via my iPad vs. having to pull out my paper notes.

My basic bread recipe for our bread maker from 2008:
http://www.hoaglun.com/blog/2008/3/23/making-bread-the-kind-that-goes-in-the-oven.html

 

Big batch artisan style bread recipe for the oven:

6 1/2 cups of flour (3 to 4 cups of white, the rest is wholewheat or 6 grain)
3 1/2 cups of water (start with 3 and add the rest if it is too dry)
1 tablespoon salt
2 tablespoons of yeast
3 tablespoons of olive oil

The following items to taste:
Brown sugar
Dried fruit (blue berries, cran berries, cherries, mixed berries, etc)
Almond, vanilla, or lemon extract
Ground orange peel

Let rise for two hours in a one gallon ice cream bucket.

Can put into fridge and use later or bake now. (If putting in the fridge let it warm/raise for 60 minutes before baking.)

Bake at 450F for 25-30 minutes