My Class E AM Transmitter with Class H Modulator

Here it is, the transmitter I originally called ‘The Hasslich’. (Coz its soooo pretty!)


I actually REALLY like the transmitted audio quality from this beast. As with most of my home-made amateur radio gear, its mostly made of scrap and junk. In fact, the case is rescued from an old auto-reverse cassette machine from the ’80s, with the rather ‘pretty’ front panel replacement made from sheet aluminium, housing the (many!) dials and knobs.

It doesn’t conform to any published Class E MOSFET transmitter design, other than my own (which is on a fag packet somewhere) (for Americans: fag packet = cigarette packet, despite what you are thinking!) and is designed for 10 Watts maximum carrier output on 160m, and around 50 Watts on 80m.

The AM transmitter uses a DDS VFO (shown top left on the front panel), with some TTL Schmitt Triggering for the VFO output buffering, followed by a single ended, parallel Class E RF deck with relay-switched filtering for 160 & 80.

For the audio, it runs at ‘high level’, Class H. Here are some waveforms of the modulation. Not bad! Now, say after me: “Ahhhhhhhhhhhhhhhhhh…”!

AM transmitter voice waveform

Bung in some tone…


Ooh, trapezoid! Remember them?


Audio filtering is switchable between 4.55 k/c and 9.6 k/c. Its a hungry bugger for bandwidth!

You may notice from the ‘say ahhhhhh!’ waveform that the rig is capable of asymmetrical positive peak modulation. On 80 metres, this rig is only just legal (to the 400 Watts PEP) because of this, despite the 50 Watts of carrier! (With ordinary, symmetrical modulation, of course, 100% modulation of a 100 Watt carrier gives 400 Watts PEP).

On 160m, this is disabled: in fact, the peaks are set to favour the negative direction to stay within the (ridiculous?!) 32 Watt PEP rule above 1850 kHz. But its nice to be able to adjust the PEP somewhat independently of carrier power! With heavy asymmetrical positive-weighted peaks on 80, the audio from this rig is FAT and LOUD! It gets great reports consistently — apart from those who think AM should sound “communications-y” (a metaphor for “rank”, in my opinion!)