The AM Forum

We all have different design objectives.  One of my design priorities is to build a compact desktop multi band PW mod AM transmitter that does not require any tuning or tuning aids or bulky components.  I have no issue with any of these things, they are just not for me. So I have been using class D with a fixed low pass filter which works fine.

I tried an experiment and rigged up a class E op filter on my test deck using a roller inductor and 2 variable caps. When it was all optimized for 7.2 mhz it was checked at 7.1 and 7.4 and found to be near identical in performance and efficiency. So the values were measured and replace with a fixed inductor on a T157-2 core and two 1KV silver mica caps.  It functions as well as a LP filter but provides about 3 to 4 % better efficiency.  Class E now wins hands down, and fully meets my requirements with this configuration.  Some scope traces attached showing Drain Pulse from one side on channel 1 (blue) and the output at the dummy load on channel 2 (yellow) at 7.1 and 7.4 mhz with no other changes.  Also the gate waveforms from the IXDD614s driving 2  C3M0280090D FETs per side at 7.4 mhz.  Just some info.

73s  Nigel

Looks fantastic! 

Just curious as to what the measured efficiency is?

Joe-W3GMS

Joe, Have 3 watt meters all read differently.  Best I can measure is 87% class D and 90% class E fixed tuned.  But the deck barely gets warm at 260W OP in class E so I think it may be a little better than that.

73s  Nigel

Calibrate those whatmeters to the scope!

Then they will all be the same at least at one power level!

I have 2 bird meters and a couple slugs that are dupes.   NONE of them match.   They are all within tolerance of each other,  though.

--Shane
KD6VXI

Thanks Nigel and a nominal 90% is nothing to complain about, especially on 40M!!

Nice work.

73, Joe-W3GMS
 

My new 40 meter fixed tuned class E deck using 6 C3M0280090D FETs is now finished and tested.  Input at carrier is 70V @ 5.4A for 381W and OP is 350W giving 92% efficiency.  Full mod shows 1.5KW peak RF.  Drivers are 2 IXDD614CIs current is 310ma total. These FETs are excellent performers on 40M.
Couple pics of Deck and friends still in bench lash-up.  Next is the box and all the other stuff.

73s  Nigel

Looks to be an excellent performer!  I do want to build something similar at some point in time. 

Now get it all packaged up and we can work on 40 meters soon.

Nice job.

Joe-W3GMS

Nigel,

Thanks for sharing the photos of your Class E transmitter.  A parts list, schematic(s), and any construction notes would be of interest.  Looking forward to hearing that transmitter on air.

73,
Brad K4RT