Technical Topics > The RF Workbench
U-LULU (Updated LULU) for 48 meters, 20 Watt Class-E AM Transmitter
Charlie_Dont_Surf:
--- Quote from: redhat on December 05, 2022, 0927 UTC ---Also, dead time control is nice but not necessary for push-pull operation. I've had PA's running at 80 meters or so with no dead time control circuitry. I even built a 2 mosfet 500W MW PA that is running in commercial service with just a 7486 setup as a phase splitter...no drive loss protection though :-\
--- End quote ---
Let's put it this way: maybe you are not explicitly controlling it and providing adjustability to it, but one way or another you are probably not cross-conducting much or at all. How that happens - or rather doesn't happen - only you can say. Otherwise, if something - anything - was not there making it not cross-conduct, either by dumb luck or intentionally prevention, you might have somewhat different results.
redhat:
:shrug: It doesn't seem to matter much until you get over 4 MHz, then things get hairy, and efficiency tends to nose-dive. My main transmitter has overlap control and drive loss protection, FWIW.
+-RH
Charlie_Dont_Surf:
--- Quote from: redhat on December 06, 2022, 0412 UTC ---:shrug: It doesn't seem to matter much until you get over 4 MHz, then things get hairy, and efficiency tends to nose-dive.
+-RH
--- End quote ---
"Quite curious, Captain."
The behavior above 4 MHz is what I would expect almost everywhere there was actual significant overlap.
Stretchyman:
I'm fine upto 15 MHz so far but then devices with a Qg of 2.2nC aren't exactly difficult to drive. Also I'm comparatively QRP in comparison!
Str.
redhat:
My 'daily driver' PA has a drive delay and protection circuit onboard, and seems fine up to 10MHz or so. I haven't investigated any higher as I feel there is little merit in doing so, and have no interest in anything above 30 meters. The simple drive circuits consisting of just an xor configured as a phase splitter start having efficiency drop off after 4 Mhz. This makes sense as the drive pulse distortion begins to be a larger fraction of on time with increased frequency Granted this was a PA I built several years ago now and there are other devices and drivers to try.
+-RH
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