In article , Cecil Moore wrote:
Ken Smith wrote:
RF transmitter power amps are certainly "impedance matched" to the
intended load. Take a look in the ARRL "The radio amateur's handbook".
If you have the 1944 addition, you will need to start reading at page 96
in the lower right column. If you don't have that, try Motorola's AN-721.

A CMOS Class-E amp is in full saturation (0.5v at 2a)
for 10% of a cycle and off (12v at 0a) for the other
90% of a cycle. The tank circuit changes the digital
energy to analog energy by filtering out everything
except the fundamental frequency component. How
in the world does one determine the steady-state
impedance of the CMOS source? Isn't the best one
can do with a digital switch is to keep it within
specified parameters? The CMOS device dissipates 2
watts for 10% of the time - therefore 0.2 watts
steady-state.

For what you say here really to be true the transistors must switch very
fast. About 25pS switching speed is needed at about 400KHz. If we take
that to be the case however, I think you will see why matching still
applies.

Lets take the reactive component first. If there is a reactive component
to the loading, the current in the switch will have a higher RMS value
without that increase in RMS increasing the radiated power of the system.
So the reactive component of the matching is fairly obvious.

Imagine that you have a well designed Class-E circuit loaded with the load
the designer optimized it for.

Now imagine that you slightly increase the resistance slightly. When you
do so, the current into the load will decrease but the voltage will not
increase enough to compensate for this.

Now lets assume that you slightly decrease the resistance. Since we are
assuming that this is a well designed case, we can assume that the
designer took steps to ensure that the output devices would be protected
from excess currents. This could be done by reducing the operating
voltage of the output section, for example. In any case, the voltage on
the load will decrease by a larger factor than the current will increase.

So it is obvious that the reactive part is matched and the resistive part
is matched just as it would be in a non-class-E output section.


--
--
forging knowledge

Ken Smith wrote:
Now lets assume that you slightly decrease the resistance. Since we are
assuming that this is a well designed case, we can assume that the
designer took steps to ensure that the output devices would be protected
from excess currents.

Let's assume the designer is an amateur who didn't provide
any protection for his tube's output. The lower the resistive
load, the more current the output device draws until it fails.
What is the output impedance of the device?
--
73, Cecil http://www.qsl.net/w5dxp


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

In article , Cecil Moore wrote:
Ken Smith wrote:
Now lets assume that you slightly decrease the resistance. Since we are
assuming that this is a well designed case, we can assume that the
designer took steps to ensure that the output devices would be protected
from excess currents.

Let's assume the designer is an amateur who didn't provide
any protection for his tube's output. The lower the resistive
load, the more current the output device draws until it fails.
What is the output impedance of the device?

At the point where it fails, the output goes to zero, I assume. If so,
wouldn't that be the impedance as I've been defining it.


--
--
forging knowledge

Ken Smith wrote:
At the point where it fails, the output goes to zero, I assume. If so,
wouldn't that be the impedance as I've been defining it.

Is an amp that fails at one minute with 100w FM
better matched than an amp that fails at two minutes
with 100w CW?
--
73, Cecil http://www.qsl.net/w5dxp


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

I read in sci.electronics.design that Cecil Moore
wrote (in ) about '1/4 vs 1/2 wavelength
antenna', on Sat, 26 Feb 2005:
Is an amp that fails at one minute with 100w FM
better matched than an amp that fails at two minutes
with 100w CW?

If the FM is what passes for music these days, it's MUCH better IMHO.
(;-)
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

In article ,
John Woodgate wrote:
[...]
If the FM is what passes for music these days, it's MUCH better IMHO.

There is very little that is sent in the form of radio waves that is worth
the electrical power to send it. The really sad thing is that much of
what is send via FM is really "voice grade" material. When FM was new,
the material for FM was specially produced to take advantage of the wide
bandwidth and large dynamic range.

--
--
forging knowledge

On Sun, 27 Feb 2005 17:12:46 +0000, Ken Smith wrote:

In article ,
John Woodgate wrote:
[...]
If the FM is what passes for music these days, it's MUCH better IMHO.

There is very little that is sent in the form of radio waves that is worth
the electrical power to send it.


Hmm, many advertisers would disagree. Since they have real money at stake
and you don't...

The really sad thing is that much of
what is send via FM is really "voice grade" material. When FM was new,
the material for FM was specially produced to take advantage of the wide
bandwidth and large dynamic range.

Bandwidth, perhaps. Wide dynamic range? The FCC rules seem to
suggest otherwise.

--
Keith

In article , Cecil Moore wrote:
Ken Smith wrote:
At the point where it fails, the output goes to zero, I assume. If so,
wouldn't that be the impedance as I've been defining it.

Is an amp that fails at one minute with 100w FM
better matched than an amp that fails at two minutes
with 100w CW?

No, you've got the concept backwards. Obviously the worst matched is the
1 o=minute case, next would be the 2 minute case and so on up to one which
runs for about its MTBF at the connected load. This last case would
likely be the one the designer was targeting.

--
--
forging knowledge

On Sun, 27 Feb 2005 17:08:23 +0000 (UTC),
(Ken Smith) wrote:

In article , Cecil Moore wrote:
Ken Smith wrote:
At the point where it fails, the output goes to zero, I assume. If so,
wouldn't that be the impedance as I've been defining it.

Is an amp that fails at one minute with 100w FM
better matched than an amp that fails at two minutes
with 100w CW?

No, you've got the concept backwards. Obviously the worst matched is the
1 o=minute case, next would be the 2 minute case and so on up to one which
runs for about its MTBF at the connected load. This last case would
likely be the one the designer was targeting.

--

It's been thirty years since I "hammed". I was only interested in the
electronics, not the talking, so I dropped out after I got a homemade
solid-state 2-meter rig running.

But I vaguely recall a 5/8 wavelength antenna that had a good
low-angle pattern.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

In article ,
Jim Thompson wrote:
[....]

But I vaguely recall a 5/8 wavelength antenna that had a good
low-angle pattern.

Unfortunately, the OP (is he still here?) was stuck with a box to short to
even fit a 1/4 wave whip. I also think that this box could not be assumed
to be resting on the ground


If you squint at the ASCII art below, you will see more or less the
radiation pattern of a 5/8 whip over a large ground plain.
.................................
.................!...............
...........******!*****..........
..........*......!......*........
..........*......!......*........
...........****..!..****...A.....
........*******..!..*******......
.....***.........!.........***...
...*.............!.............*B
********************************

If you don't have a large enough ground plain, the notch in the side
labeled "A" starts to go away and the peak at "B" reduces.


--
--
forging knowledge