[Amps] Class E amps

[Tom Thompson]

I year or so ago, I built a Class E AM transmitter with a Class D pulse 
width modulator.  The PA had a 94% efficiency and the modulator had a 
90% efficiency.  The modulator ran at 70 kHz.  Both the modulator and 
the PA used a single IRF640 Mosfet.  The transmitter put out 100 Watts 
on 160 meters.  I never got used to the small heatsinks running very cool.

Tom   W0IVJ

On 10/21/2014 12:28 PM, Manfred Mornhinweg wrote:
> Bill,
>
>> Several years ago during a RTTY contest on 40 meters I noticed a weird
>> hash noise covering the entire band. It would come and go with a
>> timing like someone was calling CQ. Tuning around, I found a station
>> whose CQ was exactly in sync with the hash. 
>
>> Later I looked him up on QRZ.com and lo and behold there he was
>> bragging about his Class E amplifier and how wonderful it was!
>
> I have also heard such stations. For example, there is a station that 
> transmits high powered AM on 40m, about 1000km from my place, using a 
> poorly made class D transmitter. It's easy to get it wrong and create 
> huge amounts of QRM, but it's also possible to do it right.
>
> I have a significant tolerance for such low quality signals, as long 
> as a station doesn't transmit it for long. If the 
> operator/experimenter puts his creation on the air, and after getting 
> reports of a dirty signal, goes on to improve it, I won't blame him 
> for the trouble caused. It's part of experimentation, which is what 
> this hobby really is about! Only when someone insists on placing a 
> dirty signal on the air, time and again, and rejects any reports that 
> tell him there is a problem, then I get sour at that guy!
>
> Digital AM transmitters are sensitive to any noise on the power 
> supply, because they operate driven into saturation, so the output 
> amplitude is proportional to the supply voltage. If a phase-shift 
> transmitter uses a switching supply, and that supply has even 1% of 
> ripple at the supply's switching frequency, then this will create 
> noticeable sidebands at that frequency from the carrier. A 50kHz dirty 
> switching supply will create QRM every 50kHz across the whole band 
> covered by the bandpass filter of the transmitter. And a noisy supply, 
> for example caused by a poor control loop, will create broadband noise 
> on the band.
>
> In addition there are all the phase modulation issues. AM people are 
> quite unsensitive to phase modulation of their signals, because in an 
> AM receiver the signal will still sound fine - but it will splatter! 
> And unwanted phase modulation is very common in FET amplifiers.
>
> I mentioned AM because it looks like the AM fans are the ones that 
> most commonly run homebrew solid state class D and class E equipment. 
> But it also applies to other modes, of course. Only that bad phase 
> distortion in SSB is quite obvious to anyone listening to the signal, 
> while in AM it's not that obvious.
>
> It's good to keep such dirty signals in mind, when developing 
> equipment that might produce them!  My method is to first measure the 
> quality of my signals as best I can, when I have built something, and 
> then when I go on the air with it for the first time, I find some hams 
> with adequate technical abilities to make a meaningful appraisal of 
> signal purity, and ask them to tune up and down while I talk to 
> someone else, and tell me if there is anything that shouldn't be there.
>
> Manfred
>
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