Hello Jim,
Tuesday, February 23, 2021
Have any schematics and / or build details been published for home build HF
band VDMOS amps? This sounds the way forward, better matching to the ubiquitous
50 Ohm antennas, no insane currents, blah blah. I am assuming this may be the
VDMOS amp you are talking about Jim?
https://www.youtube.com/watch?v=J22BXll-0vw
Any info on practical HF VDMOS amps welcome!
Best regards,
Chris mailto:chris@chriswilson.tv
JT> Date: Sat, 13 Feb 2021 14:03:03 -0500
JT> From: "Joe Subich, W4TV" <lists@subich.com>
JT> To: amps@contesting.com
JT> Subject: Re: [Amps] Clipperton L - GI-7B
JT> <All of this is a result of using output devices rated for saturated
JT> <power output at 12 Volts. If one looks at the spec sheets for all
JT> <of the devices used in the mentioned transceivers, *IF* the spec
JT> <sheet shows parameters for IMD, it will be significantly better at
JT> <60 to 80 W PEP than at 100 W PEP.
JT> <Amateur transceiver manufacturers *MUST* get their design heads out
JT> <of where the sun don't shine and start using 24V devices for 100W
JT> <power levels and 48V devices for 200W power levels. Driving solid
JT> <state amplifiers well past the 1 dB compression point guarantees
JT> <IMD3 worse than -30 dB and it is time to stop accepting such garbage.
JT> <73,
JT> < ... Joe, W4TV
JT> ## Funny thing is, the Icom marine 100 watt xcvrs are 10 db
JT> better for IMD, vs the Icom ham junk specs.....
JT> and both operate on 12 vdc. The marine versions use a lot more NFB.
JT> ## On another note, while LDMOS might be all the rage for 1.5
JT> kw SS amplifiers, VDMOS devices offer more simplicity.
JT> They, microseimi now have VDMOS devices up to 700 vdc. This
JT> simplifies a lot of things. Like an output Z of 50 ohms for
JT> 150 watts pep out...when run at 125 vdc.
JT> ## A buddy in CT designed and built a 2-3 kw pep output
JT> VDMOS amp, that will operate on either 120 vac..or 240 vac. Run on 120
vac,
JT> it uses 2 x separate power supplies, with inputs in
JT> parallel..and isolated outputs. On 240 vac, same 2 x power
JT> supplies used, again, with isolated outputs.
JT> Kicker is, NO xfmr used. And yes, the entire chassis is
JT> bonded to the green ground wire. It senses the drive level, and
JT> freq, and if drive is too high, the relays
JT> wont even activate. If drive is a normal level, then
JT> increased, it will kick offline. If it overheats, it kicks
JT> offline. It’s got 8 levels of protection built into it,
JT> you just cant blow it up, or damage it. So far. so good.
JT> Bunch of testing being done on it this week. Stay tuned.
JT> Jim VE7RF
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