>"And why on earth should I use two power supplies in series, instead of
using a single one of the proper voltage? I fail to see the point!"
Because 50V-55V @ 50A supplies are plentiful through the telecom surplus
market. For example, I recently purchased a NOS 3KW Eltek Flatpack2
switching supply for use with a 1500W LDMOS amplifier. It's an incredibly
compact and reliable design, made exclusively for telecom. Price was about
USD $100 for a unit in an unopened box.
Paul
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Manfred
Mornhinweg
Sent: Tuesday, April 25, 2017 4:37 PM
To: amps@contesting.com
Subject: Re: [Amps] Price per Watt Conversation
Jim,
> ## I was afraid of this. We are back to square one. 50% eff and
> lousy imd, or better IMD and lousy 35% eff..take your pick.
Yes. You see? That's why I think that we need to look forward, forget
conventional old-fashioned class AB linear amplifiers, and develop a better,
higher efficiency, cleaner concept. The broadband push-pull low impedance
class AB amplifiers, with all of their problems, have been the workhorse
since about 1975. That's over 40 years. Even the general move from bipolar
transistors to MOSFETs has changed very little about their basic design and
performance. It's high time that we move on to something better. It's not a
matter of doctoring around the old design trying to fix its unfixable
shortcomings. It's about designing something new! And it's about not being
afraid of doing something new!
> ## You may well be able to put 2 x 50-60 vdc switching supplies in
> series to obtain your 100-120 vdc for your proposed
And why on earth should I use two power supplies in series, instead of using
a single one of the proper voltage? I fail to see the point! Maybe if I had
two 50-60V supplies lying around... But if I have to build or buy them, I
can as well go for a single one of the proper rating! 100V switching
supplies are slightly simpler and cheaper to build than 50V ones of the same
power.
> ## baffles me how SS marine xcvrs all have superb IMD..and also run
> on 11-15 vdc.
The ones I have worked on are designed much like ham equipment, and have
much the same basic performance. Except for one important difference:
While ham transceivers are full of knobs to give hams something to play
with, marine and other professional radios have as few knobs as possible, to
simplify operation. After all they are intended to be used by largely
radio-ignorant people, who want to get communication, not to play with
radios. So the microphone gain, drive level, etc, are fixed, or internally
adjusted at the factory, to those values that give a correct and clean
signal when speaking quite loudly into the microphone.
After all, most operators of such radios tend to shout, and the environment
is often noisy.
Hams instead get to play with mic gain, compression level, drive level, and
often they add non-original mikes having further level and compression
adjustments. And most hams just LOVE to deflect the needles as far as they
possibly can. The result is: All knobs fully to the right, resulting in
tremendously excessive gain, with the ALC fighting it. Add a poorly designed
ALC, and many are, and that's it.
Some hams go another step further, take the cover off their radios and
defeat the ALC. That goes a good way toward deflecting the needles even
further. And toward splattering all over the band and then some, of course.
Hams should be asked to pass a test, both about technical knowledge and
mental sanity, before being allowed to operate radios that have external
controls for mic gain and compression level. Those who haven't passed that
test should only operate radios that don't have these controls, and only
operate them with the stock mikes. And the covers of their radios should be
welded shut, just in case! :-)
Joe,
just a small correction:
> The PA must be over driven in order to produce any ALC!
That depends on how it's implemented. An ALC that requires overdriving is a
badly designed ALC. In solid state transceivers the ALC signal is usually
derived from a comparator that starts giving an output when either the power
output reaches a certain level, or the reflected power does so. If this
comparator is properly adjusted so that it starts giving an output a little
before the PA is overdriven, then the ALC prevents overdriving. Of course if
a monkey with a screwdriver fiddles with that internal adjustment and sets
it above the overload level, the ALC can no longer do its job of preventing
overdrive.
Another problem is that the ALC usually doesn't know what's the actual
saturation threshold of the PA. And this level changes with the supply
voltage. So, if at the factory the ALC threshold is adjusted so that at
13.8V supply voltage it works fine and triggers just before overload, then
when running that same radio at 12.0V (long cables, battery
operation) the PA will saturate and splatter. That's a very real problem we
can hear on the bands every day. Only radios with internal, good voltage
regulation for the PA are free from this problem. All the 13.8V radios are
not, and that's what most hams use.
And then, many ALC circuits are designed with inadequate time constants.
These will produce a single burst of splatter at every strong voice attack,
but not during continuous talking. The higher the operator sets the gain
controls, the worse this gets. But only on the attacks.
Manfred
========================
Visit my hobby homepage!
http://ludens.cl
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