[Milsurplus] Calling Smart People: Class D Transmitter

[don davis]

Yes.  We used LT for most drive and control in space equip.  Very good parts
and people.  The only limit I see is the current vs freq chart that only
goes up to 1 MHz.  Boo, that's what I was afraid of.  But, might work ok if
the rest of operation is well de-rated from SOAR limits.  They also have
some high-voltage, high power, and "fast" rated parts that might be more
appropriate.  You have to be very careful driving resonant ckts with FETs
due to high voltages and currents you might find.  They have some good
tutorial ap-notes as well, avail from the sales reps (I tossed ~ 100 lbs of
their stuff when I retired 2 years ago...).  Make sure your expectations are
within reasonable limits - you won't get the very high efficiency that the
beacon boys get (they need high eff due to limited input power and short
antennas).  But then, that's not a concern for 40M fun.

Re: 375 tube replacements:  Bravo!  Nice work.  These old xmtrs are worse
than useless (as it stands now) due to the tubes being far more valuable
than any utility a fully operational system would have.  Like using a lump
of gold for a magazine pile paperweight in your doctor's office.  I've toyed
with the idea of tetrode / pentode operation (807? 937? Sweep tube?)  but
have never been motivated enough.  Maybe 814 0r 828 since these were used in
many Navy sets?   One thing to bear in mind re: plate choke:  It is very
difficult to design a wide-band choke for an entire freq range, as opposed
to a ham-bands only choke.  Millen, Henry, et al sold a lot of ham band
segmented chokes that might be exactly what you need - just don't power it
up out-of-band...

73 de don ad6pb

-----Original Message-----
From: Milsurplus [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of
David Stinson
Sent: Monday, February 02, 2015 4:37 AM
To: boatanchors at mailman.qth.net; milsurplus at mailman.qth.net
Subject: Re: [Milsurplus] Calling Smart People: Class D Transmitter

(yes I promise it's boatanchor- working on a driver)

Re: Driving the MOSFET Hi-C inputs.

What do ya'll think of the new class of devices specifically designed to
drive MOSFETs?

Here's an example of one that can do 360 degrees in 15 ns and stay "square"
while driving a 3000 pFd load:

http://cds.linear.com/docs/en/datasheet/4449fa.pdf
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