Added to the panel were a 5A DC meter to monitor drain current, a keying jack and a key shorting-switch for keydown testing. This is the third version I have built using the design on Roger's page, with all three performing pretty much as advertised. It is an inexpensive, easily reproducible design.
I made one small change in the third version (above) by adding an additional FET in parallel with the single IRF540 thus cutting heating dissipation as described in an earlier blog. At normal CW keying speeds, no heatsinking seems needed on this particular version, when operated on 12VDC. Anything a little higher or any QRSS modes would require heatsinking. I did eventually add two small heatsinks in case I chose to run QRSS at some point.
When operated at 12-13V, the measured output power is around 25W while at 22-23V, the output is around 70W. I suspect that you could get in excess of 100W out, at higher voltages and larger heatsinking or by blowing the sink with a small fan.
The main function for the new transmitter will likely be as a semi-permanent beacon as well as for a small signal source when tuning the antenna. I may also use it in the WSPR mode with a modification to the oscillator section. One particularly nice feature with the Class-E design is that with no load at all, the current drops to almost zero, should the antenna suddenly fail.
If you live in VE7 or across the border in W7 land, please have a listen on 475.0 KHz and let me know if you can hear the "VVV" beacon over the next few days!
Heard your VVV beacon last night (September 18) in Surrey, BC at about 10:30 PDT with my "ultralight" Sony SRF-59 radio. I have aligned the radio so I can receive NDBs at the "high" end of the long wave band. Your signal managed to get through the noise of ADSL routers and Plasma TVs okay.
Hi Greg - very nice to get your report and mp3 file of my beacon signal! Maybe we can work on 630m one of these days!!
73 / Steve
Thanks Juan. It's a very easy / forgiving circuit to duplicate.
Hey Steve, a question for you about the paralleling of the two 540 FET's
Does paralleling change the impedances so that it affects the output filter circuit ?? In other words, do I need to modify my LP output filter if I put another FET in parallel with my existing circuit (the GW3UEP amp) ?
73, Neil Klagge, w0yse, wg2xsv
Hi Neil...if it changes the impedance, I think it must be minimal, so I would say 'no'. There will be no increase in power output of course, just a cooler running PA. If you already have a cool running PA, the changes may not necessarily be worth the effort. If you are keen on running more power, the easiest way (in my opinion) is to build two (or more) identical amps and run them through a power combiner.
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