On Tue, 11 May 2004 16:41:22 +0200, "Marc Battyani"
wrote:

But my problem for the impedance matching is that I don't know the amplifier
output impedance.
It's a basic class-E amplifier (A self + an IRL510 MOSFET)
Is there a simple way to measure it or to compute it ?

Thanks,

Marc

Hi Marc,

For actual specifics of your device, go to:
http://www.irf.com/product-info/data...ata/irl510.pdf
The answer to your literal question requires more details of the
circuit, as the device shows a drain-source resistance that is common
of many finals transistors found in 100W amateur transmitters which
typically exhibit a 50 Ohm source Z at rated power.

This exhibited characteristic Z is a consequence of Z multiplication
through conventional transformer theory. These designs also have the
benefit of low pass filters aiding a smooth transition of Z from the
device Z on the order of 0.5 to 1 Ohm to the System Z of 50 Ohms.

If your amplifier lacks in these regards, it will suffer in efficiency
in spite of the claims of designs of its class. You may wish to
consider driving a small antenna directly to aid in matching. This is
because very small antennas (once the reactances are balanced out, an
important consideration) exhibit a much smaller load resistance that
corresponds to your device's natural output Z. However, to maintain
efficiency, you will need to be scrupulous about all Ohmic sources of
loss that come from construction issues.

73's
Richard Clark, KB7QHC

Amateur radio transmitters do NOT typically exhibit a source Z of 50 ohms at
rated power or any other power.

A conjugate match does NOT exist. It cannot play any part in transmitter
design.

Actual source Z, whatever its value, appears purely by chance AFTER the
design has been completed.

Even the designer doesn't know what value it might turn out to be. And the
amateur radio transmitter user couldn't care two hoots what it is.

I thought this had all been settled a few years back. But no! It seems the
Old Wives are still plagiarising each other.
---
Reg

On Wed, 12 May 2004 04:21:19 +0000 (UTC), "Reg Edwards"
wrote:

Amateur radio transmitters do NOT typically exhibit a source Z of 50 ohms at
rated power or any other power.

Creaky yarn spinning that went out with high button shoes.

A conjugate match does NOT exist. It cannot play any part in transmitter
design.

A tale told to unruly hams by curmudgeons to shut them up.

Actual source Z, whatever its value, appears purely by chance AFTER the
design has been completed.

Wishful thinking in its full technicolor and surround sound glory.

Even the designer doesn't know what value it might turn out to be. And the
amateur radio transmitter user couldn't care two hoots what it is.

Called projection of wish fulfillment.

I thought this had all been settled a few years back. But no! It seems the
Old Wives are still plagiarising each other.

Self fulfilling prophecy.
---
Reg

Who's Reg?

This was MUCH too tempting to pass up for another chuckle. The number
of logical inconsistencies within this short gasp begged further
illumination:

On Wed, 12 May 2004 04:21:19 +0000 (UTC), "Reg Edwards"
wrote:

Amateur radio transmitters do NOT typically exhibit a source Z of 50 ohms at
rated power or any other power.
....
Actual source Z, whatever its value, appears purely by chance AFTER the
design has been completed.

It thus follows there must be SOME Z exhibited, any value of which
occurs by happenstance and whose effect, easily determined, is a
probabilistic spin of the chambers in a capitalistic russian roulette
in the market place. Imagine trying to sell your rigs with this wild
inconsistency in quality and performance. 80% of your product would
be RMA'd to oblivion and your production line brought to its knees
with the loading docks running in reverse. Talk about a mismatch in
THAT line - I love it! We have a description of a conceptual death
wish embraced with a vengeance.

Even the designer doesn't know what value it might turn out to be. And the
amateur radio transmitter user couldn't care two hoots what it is.

Which, of course has been invalidated by the mere asking of the
question that lead to this thread. Boy, self snuffing predictions
come fast and furious. It would be so much more gothic if only there
were numbers behind this dire brooding.

This was better than any Dago Red you happen to be slugging down, Reg.
Do you write this stuff while looking through the bottom of the glass?
If you simply let yourself go, we could have a tale told by Heathcliff
pining for Catherine from the moors.

It seems the Old Wives are still plagiarising each other.
Yours was just syllables short of being lifted from Emily Brontë.

73's and thanx for the opportunity, I will of course allow you the
last comment ;-)
Richard Clark, KB7QHC

Sorry to say I've never read Emily Bronte. My style of writing has been
likened to Neville Shute but I've never read him either. Only seen films.

But I do believe fact is stranger than fiction.

Hi Richard,

En Richard Clark va escriure en Wed, 12 May 2004 00:32:35 GMT:

These designs also have the
benefit of low pass filters aiding a smooth transition of Z from the
device Z on the order of 0.5 to 1 Ohm to the System Z of 50 Ohms.

This is something I have always thought: When driving loops, very
short monopoles (VLF) or other low-impedance antennas, why raise
transmitter Z to 50 ohms, send it through the line and lower it
again to whatever required? Couldn't the amplifier be built
directly at the antenna base so _no_ transmission line is
required and couple directly the low Z at the final transistor(s)
to the low Z at the antenna?

Aside, for VLF, audio is usually transferred at 8, 4 or even 2
ohms. VLF is not that far apart from audio, only 1 decade higher.

73s

Toni - EA3FYA

Toni wrote:
This is something I have always thought: When driving loops, very
short monopoles (VLF) or other low-impedance antennas, why raise
transmitter Z to 50 ohms, send it through the line and lower it
again to whatever required?

40-50 years ago, we had to lower the transmitter Z usually with
a built-in adjustable pi-net tuner.
--
73, Cecil http://www.qsl.net/w5dxp



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Hi Cecil

En Cecil Moore va escriure en Wed, 12 May 2004 09:44:10 -0500:

40-50 years ago, we had to lower the transmitter Z usually with
a built-in adjustable pi-net tuner.

Do you mean before the existence of electronic simulators, when
people actually build electronic apparatus? :^) When I studied
electronics I was in the last course where students would
actually build things. From the next course on student's
practices would be made only by computer simulations :^(

As to your comment, I know valves exist but I have never learned
/ been taught how to use them. :^(

73s

Toni - EA3FYA

On Wed, 12 May 2004 10:13:10 +0200, Toni wrote:

This is something I have always thought: When driving loops, very
short monopoles (VLF) or other low-impedance antennas, why raise
transmitter Z to 50 ohms, send it through the line and lower it
again to whatever required? Couldn't the amplifier be built
directly at the antenna base so _no_ transmission line is
required and couple directly the low Z at the final transistor(s)
to the low Z at the antenna?

Hi Toni,

Exactly!

73's
Richard Clark, KB7QHC

"Toni" wrote
En Richard Clark va escriure en Wed, 12 May 2004 00:32:35 GMT:

These designs also have the
benefit of low pass filters aiding a smooth transition of Z from the
device Z on the order of 0.5 to 1 Ohm to the System Z of 50 Ohms.

There is 0.5 Ohm when the transistor is on but not when is it off. So the
resulting impedance should probably be more than that. ??

This is something I have always thought: When driving loops, very
short monopoles (VLF) or other low-impedance antennas, why raise
transmitter Z to 50 ohms, send it through the line and lower it
again to whatever required? Couldn't the amplifier be built
directly at the antenna base so _no_ transmission line is
required and couple directly the low Z at the final transistor(s)
to the low Z at the antenna?

This is what I have. The amplifier is directly connected to the loop.

Here is a scope screen copy of the output of the amplifier:
http://www.fractalconcept.com/scope-screen.jpg

The C2 trace is the drain voltage and the C3 one is the 50 Ohm resistor
voltage.

The schematics is very simple:
http://www.fractalconcept.com/schema.pdf

The first one is the one that works on the scope screen.
The second one is a one that does not work at all: the torus of the 680nH
melted

I have a little more success by just connecting the drain to the loop
through a capacitor but it's still not good (25% efficiency)

Any idea ?

Marc